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1987 Volume 3 Issue 4
1987, 3(04): 337-340
doi: 10.3866/PKU.WHXB19870401
Abstract:
Studies on the photofragmentation of n-C_3H_7I and i-C_3H_7I have been carried out by a photofragment spectrometer with rotatable pulsed molecular beam crossed with KrF excimer laser beam. TOF spectra of the iodine atom fragments (Fig.1, 2) which show the separation of the primary photodissociation channels
n-C_3H_7I→n-C_3H_7+I~*(~2P_(1/2))
n-C_3H_7+I(~2p_(3/2))
i-C_3H_7I→i-C_3H_7+I~*(~2P_(1/2))
i-C_3H_7+I(~2P_(3/2))
are obtatned at 12 different angles. The distribution of total translational energy E_(CM) of recoiling photofragments are then determined. The ratios I~*/I of the photodissociation channels of n-C_3H_7I and i-C_3H_7I are measured to be 1.61 and 0.96 respectively (Table 1). The ratios I~*/I obtained by photofragment translational energy measurement in this Lab~[3]. are od in agreement with most of results abtained by IR emission~[5] and LIF~[4] measurement except the data of i-C_3H_7I, which is much different from I~*/I=0.35 reported by Bershon~[4] using LIF method.
The extent of internal alkyl fragment excitation E_(int)~R is also determined (Table 2) by energy balance. The fraction of the available energy (E_(av1)=E_(CM)+E_(int)~R) which es into internal exciatation of the alkyl fragment increases from 12.5% for I~* channe of CH_3I to 64% for both channels of i-C_3H_7I. The results are consistent with direct impulsive dynamic model of unimolecular decomposition based on “soft” alkyl radicals.
The facts that the ratio I~*/I decreases with increasing carbon atoms and that the difference of the internal excitation of alkyl radicals between the I~* (~2P_(1/2)) and I (~2P_(3/2)) channelsincreases with increasing carbon atoms should be related and important for better understanding the origin of the I(~2P_(3/2)) channel caused by the potential energy surface crossing~[3]. The results of the internal excitation of the alkyl radicals in the photodissociation are also valuable for prediction of secondary products during the UV photolysis of those alkyl iodides in the gas cell.
Studies on the photofragmentation of n-C_3H_7I and i-C_3H_7I have been carried out by a photofragment spectrometer with rotatable pulsed molecular beam crossed with KrF excimer laser beam. TOF spectra of the iodine atom fragments (Fig.1, 2) which show the separation of the primary photodissociation channels
n-C_3H_7I→n-C_3H_7+I~*(~2P_(1/2))
n-C_3H_7+I(~2p_(3/2))
i-C_3H_7I→i-C_3H_7+I~*(~2P_(1/2))
i-C_3H_7+I(~2P_(3/2))
are obtatned at 12 different angles. The distribution of total translational energy E_(CM) of recoiling photofragments are then determined. The ratios I~*/I of the photodissociation channels of n-C_3H_7I and i-C_3H_7I are measured to be 1.61 and 0.96 respectively (Table 1). The ratios I~*/I obtained by photofragment translational energy measurement in this Lab~[3]. are od in agreement with most of results abtained by IR emission~[5] and LIF~[4] measurement except the data of i-C_3H_7I, which is much different from I~*/I=0.35 reported by Bershon~[4] using LIF method.
The extent of internal alkyl fragment excitation E_(int)~R is also determined (Table 2) by energy balance. The fraction of the available energy (E_(av1)=E_(CM)+E_(int)~R) which es into internal exciatation of the alkyl fragment increases from 12.5% for I~* channe of CH_3I to 64% for both channels of i-C_3H_7I. The results are consistent with direct impulsive dynamic model of unimolecular decomposition based on “soft” alkyl radicals.
The facts that the ratio I~*/I decreases with increasing carbon atoms and that the difference of the internal excitation of alkyl radicals between the I~* (~2P_(1/2)) and I (~2P_(3/2)) channelsincreases with increasing carbon atoms should be related and important for better understanding the origin of the I(~2P_(3/2)) channel caused by the potential energy surface crossing~[3]. The results of the internal excitation of the alkyl radicals in the photodissociation are also valuable for prediction of secondary products during the UV photolysis of those alkyl iodides in the gas cell.
1987, 3(04): 341-344
doi: 10.3866/PKU.WHXB19870402
Abstract:
Quantitative pertubational molecular orbital method (PMO) has been found to be very useful for interpretation and prediction of the structure-property relations. However,there is yet no such method for polymers and crystal. In this work, we have developed a quantitative pertubational crystal orbital method (PCO) within the framework of ab initio SCF-CO theory. In this procedure, the unit cell is divided into fragments, and the fragmental crystal orbitals are calculated by ab initio SCF- CO method. Then by meas of pertubation theory, the interaction between the fragmental crystal orbital can be calculated, and the properties of crystal or polymers are analyzed from the point of view of the interactions between the fragmental crystal orbitals.
If the composite polymer is —(AB)—_n, and the fragmental polymers are —(A)—_n and —(B)—_n, then from pertubation theory , we have the first order and second order correction for energy of the ith band with wave vector k:
E_i~((2)k)=-Σ_(h(≠i) {|Δ_(i j)~k-S_(i j)~kE_i~((0)k)|~2}/{E_j~((0)k)-E_i~((0)k)}
where Δ_(i j)~k and S_(i j)~k are the matrix elements of the followong matrix respectively:
Δ~k=C~((0)k+)δF~kC~((0)k), S~k=C~((0)k+)s~kC~((0)k)
and
δF=[F_A~k-F_A~((0)k) F_(AB)~k C~((0)k)=[C_A~((0)k) O
F_(AB)~(k+) F_B~k-F_B~((0)k)], O C_B~((0)k)]
S~k is the overlap matrix when atomic orbitals are used as basis set and the S~k isthe overlap matrix when fragmental crystal orbitals are used as basis set.
Analo us to the treatment of PMO, we can define the useful terminology “two-electron stabilization and four-electron destabilization” as follows:
If Ψ_i~((0)k) is a doubly occupied fragmental crystal orbital, Ψ_j~((0)k) is an unccupied fragmental crystal orbital, then the term
2|Δ_(i j)~k-E_i~((0)k)S_(i j)~k|~2/(E_i~((0)k)-E_j~((0)k))
approximates the two-electron tabilization interaction energy between Ψ_i~((0)k) and Ψ_j~((0)k).
If both Ψ_i~((0)k) and Ψ~((0)k) are doubly occupied, the term
[2/(1-|S_(i j)~k|~2)[{(E_i~((0)k)+E_j~((0)k))|S_(i j)~k|~2-2[Δ_(i j)~k(R)S_(i j)~k(R)+Δ_(i j)~k(I)S_(i j)~k(I)]}
may be regarded as the four-electron destabilization interaction energy between Ψ_i~((0)k) and Ψ_j~((0)k). (where (R), (I) represent the real part and imaginary part respectively.
For illustration, we have performed ab initio SCF-CO calculation and PCO calculation on several one dimensional polymers, they are polymethylacetylene, polymonocyanoacetylenes and polyfluoroacetylene. We have explained quite well the effects of substituents (CH_3, CN F) on the π band structure of the polymers from the interaction between the π crytal orbital of the substituents with the π crystal orbitals of the backbone. The details of this work will be published later.
Quantitative pertubational molecular orbital method (PMO) has been found to be very useful for interpretation and prediction of the structure-property relations. However,there is yet no such method for polymers and crystal. In this work, we have developed a quantitative pertubational crystal orbital method (PCO) within the framework of ab initio SCF-CO theory. In this procedure, the unit cell is divided into fragments, and the fragmental crystal orbitals are calculated by ab initio SCF- CO method. Then by meas of pertubation theory, the interaction between the fragmental crystal orbital can be calculated, and the properties of crystal or polymers are analyzed from the point of view of the interactions between the fragmental crystal orbitals.
If the composite polymer is —(AB)—_n, and the fragmental polymers are —(A)—_n and —(B)—_n, then from pertubation theory , we have the first order and second order correction for energy of the ith band with wave vector k:
E_i~((2)k)=-Σ_(h(≠i) {|Δ_(i j)~k-S_(i j)~kE_i~((0)k)|~2}/{E_j~((0)k)-E_i~((0)k)}
where Δ_(i j)~k and S_(i j)~k are the matrix elements of the followong matrix respectively:
Δ~k=C~((0)k+)δF~kC~((0)k), S~k=C~((0)k+)s~kC~((0)k)
and
δF=[F_A~k-F_A~((0)k) F_(AB)~k C~((0)k)=[C_A~((0)k) O
F_(AB)~(k+) F_B~k-F_B~((0)k)], O C_B~((0)k)]
S~k is the overlap matrix when atomic orbitals are used as basis set and the S~k isthe overlap matrix when fragmental crystal orbitals are used as basis set.
Analo us to the treatment of PMO, we can define the useful terminology “two-electron stabilization and four-electron destabilization” as follows:
If Ψ_i~((0)k) is a doubly occupied fragmental crystal orbital, Ψ_j~((0)k) is an unccupied fragmental crystal orbital, then the term
2|Δ_(i j)~k-E_i~((0)k)S_(i j)~k|~2/(E_i~((0)k)-E_j~((0)k))
approximates the two-electron tabilization interaction energy between Ψ_i~((0)k) and Ψ_j~((0)k).
If both Ψ_i~((0)k) and Ψ~((0)k) are doubly occupied, the term
[2/(1-|S_(i j)~k|~2)[{(E_i~((0)k)+E_j~((0)k))|S_(i j)~k|~2-2[Δ_(i j)~k(R)S_(i j)~k(R)+Δ_(i j)~k(I)S_(i j)~k(I)]}
may be regarded as the four-electron destabilization interaction energy between Ψ_i~((0)k) and Ψ_j~((0)k). (where (R), (I) represent the real part and imaginary part respectively.
For illustration, we have performed ab initio SCF-CO calculation and PCO calculation on several one dimensional polymers, they are polymethylacetylene, polymonocyanoacetylenes and polyfluoroacetylene. We have explained quite well the effects of substituents (CH_3, CN F) on the π band structure of the polymers from the interaction between the π crytal orbital of the substituents with the π crystal orbitals of the backbone. The details of this work will be published later.
1987, 3(04): 345-350
doi: 10.3866/PKU.WHXB19870403
Abstract:
Using an excimer pumped dye laser system, the multiphoton ionization MPI spectrum PH_3 was investigated between 300-640 nm. More than 20 bands have been recorded and a primary assignment has been made.
Near 20 bands observed in the range of 351-398 nm (Fig.3) are suggested to be a (2+1) excitation via PH_3 (Ã) state which was continuum observed in the absorption spectra. However, an estimated lifetime of 5×10~(-13) s for PH_3 (Ã) state still allows a subseqent excitation with a rate of 10~(12) s~(-1). The spectral bands of (Ã←X) exhib and an average interval of 263 cm~(-1).
Some weak bands between 460—495 nm are asigned to be (3+1) ionization via B state. A new formula [Formula (2)] modifies the original one which was suggested by Humphiries et al.~[1].
Six bands in 428—452 nm and four bands in 385—398 nm are assigned to the (3+1) MPI spectra via C and D states respectively. The term value of D state is estimated to be≤75567 cm~(-1), and ω_0 is about 510 cm~(-1).
Using an excimer pumped dye laser system, the multiphoton ionization MPI spectrum PH_3 was investigated between 300-640 nm. More than 20 bands have been recorded and a primary assignment has been made.
Near 20 bands observed in the range of 351-398 nm (Fig.3) are suggested to be a (2+1) excitation via PH_3 (Ã) state which was continuum observed in the absorption spectra. However, an estimated lifetime of 5×10~(-13) s for PH_3 (Ã) state still allows a subseqent excitation with a rate of 10~(12) s~(-1). The spectral bands of (Ã←X) exhib and an average interval of 263 cm~(-1).
Some weak bands between 460—495 nm are asigned to be (3+1) ionization via B state. A new formula [Formula (2)] modifies the original one which was suggested by Humphiries et al.~[1].
Six bands in 428—452 nm and four bands in 385—398 nm are assigned to the (3+1) MPI spectra via C and D states respectively. The term value of D state is estimated to be≤75567 cm~(-1), and ω_0 is about 510 cm~(-1).
1987, 3(04): 351-356
doi: 10.3866/PKU.WHXB19870404
Abstract:
The reactions between cobalt xanthates, CoA_3(A=RXan), and dimethylamine are investigated by means of high-performance liquid chromatography(HPLC). The reaction mixtures, containing CoA_3, CoA_2B, CoAB_2, and CoB_3(B=dimethyl dithiocarbamate), are separated on a Zorbax-sil column by mixed eluent of n-hexane and isopropanol (90:10). The retention times of the complexes are found to be increasing with the increase of the number of dimethyldithiocarbamate ligand in the complexes, i.e. CoB_>CoB_2A>CoBA_2>CoA_3(Fig.1, Fig.2). Further HPLC study shows that the reaction involve three steps of substitutions. The -OR groups are replaced one after another by-NMe_2 group (Fig.3). A new reacton product, dimethylthiourethane, is also discovered. Kinetic study on the first step of substitution in n-hexane reveals that the reactions are first order to cobalt complexes and 3rd order to dimethylamine (Fig.4, Table 1). The rate constants at 298 K for the complexes increase in the series, Co(EtXan)_3, Co(MeXan)_3, Co(BzXan)_3. The reaction mechanism is discussed and the present results favour the nucleophilic substitution prediction.
The reactions between cobalt xanthates, CoA_3(A=RXan), and dimethylamine are investigated by means of high-performance liquid chromatography(HPLC). The reaction mixtures, containing CoA_3, CoA_2B, CoAB_2, and CoB_3(B=dimethyl dithiocarbamate), are separated on a Zorbax-sil column by mixed eluent of n-hexane and isopropanol (90:10). The retention times of the complexes are found to be increasing with the increase of the number of dimethyldithiocarbamate ligand in the complexes, i.e. CoB_>CoB_2A>CoBA_2>CoA_3(Fig.1, Fig.2). Further HPLC study shows that the reaction involve three steps of substitutions. The -OR groups are replaced one after another by-NMe_2 group (Fig.3). A new reacton product, dimethylthiourethane, is also discovered. Kinetic study on the first step of substitution in n-hexane reveals that the reactions are first order to cobalt complexes and 3rd order to dimethylamine (Fig.4, Table 1). The rate constants at 298 K for the complexes increase in the series, Co(EtXan)_3, Co(MeXan)_3, Co(BzXan)_3. The reaction mechanism is discussed and the present results favour the nucleophilic substitution prediction.
1987, 3(04): 357-361
doi: 10.3866/PKU.WHXB19870405
Abstract:
The spectrum of AsH_2(Ã ~2A_1-X ~2B_1) from 402 nm to 650 nm was first ob- served via ArF laser photolysis of AsH_3. Seven band series were assigned and the relation v=19928+868v′2-3v′2~2- (987v″_2-6v″_2~2) was obtained. The radiative lifetime of (130±20)ns was measured for AsH_2(Ã ~2A_1). Emission spectra from nascent As atom and a multiphoton ionization signal were obtained.
The spectrum of AsH_2(Ã ~2A_1-X ~2B_1) from 402 nm to 650 nm was first ob- served via ArF laser photolysis of AsH_3. Seven band series were assigned and the relation v=19928+868v′2-3v′2~2- (987v″_2-6v″_2~2) was obtained. The radiative lifetime of (130±20)ns was measured for AsH_2(Ã ~2A_1). Emission spectra from nascent As atom and a multiphoton ionization signal were obtained.
1987, 3(04): 362-367
doi: 10.3866/PKU.WHXB19870406
Abstract:
A differential calorimeter which operates in the range of 600-1500 K was con- structed on the basis of DTA principle. This apparatus has some modifications up- on Hoster's calorimeter. Its reliability was proved by measuring some systems whose enthalpies of formation or phase transformation have been given out in the published literatures.
The calorimeter was used to determine the enthalpies of formation of 9 alloys (with x_Fe=0.53) of Fe-Cr-V system, which no one up to now has measured except Malinsky and Claisse who did only one of these alloys. We also used it to determine the enthalpies of the sigma-alpha phase transformation of these alloys. The data obtained in present work were compared with that of Malinsky and Claisse for the ternary system, Dench and Spencer for the binary systems, and od coincidence was found between them. The experimental results thow that on the pseudobinary system of x_Fe=0.53, the enthalpies of formation of bcc Fe-Cr-V alloys change its sign from positive on the Fe-Cr side to negative on the Fe-V side.
A differential calorimeter which operates in the range of 600-1500 K was con- structed on the basis of DTA principle. This apparatus has some modifications up- on Hoster's calorimeter. Its reliability was proved by measuring some systems whose enthalpies of formation or phase transformation have been given out in the published literatures.
The calorimeter was used to determine the enthalpies of formation of 9 alloys (with x_Fe=0.53) of Fe-Cr-V system, which no one up to now has measured except Malinsky and Claisse who did only one of these alloys. We also used it to determine the enthalpies of the sigma-alpha phase transformation of these alloys. The data obtained in present work were compared with that of Malinsky and Claisse for the ternary system, Dench and Spencer for the binary systems, and od coincidence was found between them. The experimental results thow that on the pseudobinary system of x_Fe=0.53, the enthalpies of formation of bcc Fe-Cr-V alloys change its sign from positive on the Fe-Cr side to negative on the Fe-V side.
1987, 3(04): 368-374
doi: 10.3866/PKU.WHXB19870407
Abstract:
The reduction process of murexide (or ammoniumm purpurate) has been inves- tigated at ld minigrid electrode in optically transparent thin-layer cell, using UV-VIS spectroscopy technique. From the experimental results of thin-layer cyclic voltammograms of murexide (or purpurate ion) in different pH system and UV-VIS spectra from the reduction of purpurate ion obtained in situ by spectro- electrochemistry, it was found that the reduction of purpurate ion is a two electron transfer irreversible process, accompanied with a subsequent chemical reaction at pH<8 in which the reduction product, dibarbituylamine decomposed into uramil and barbituric acid. In addition, the formal potential, E~0′ and electron transfer number, n were calculated from spectra at different potentials. Double potentialstep chronoabsorptometry was employed for measuring the decomposition rate constant of dibarbituylamine. The pseudo-firstorder rate constants at pH4.0, 5.0, 5.5 and 6.4 were 6.6, 5.0, 3.4 and 2.6×10~(-4) s~(-1), respectively.
The reduction process of murexide (or ammoniumm purpurate) has been inves- tigated at ld minigrid electrode in optically transparent thin-layer cell, using UV-VIS spectroscopy technique. From the experimental results of thin-layer cyclic voltammograms of murexide (or purpurate ion) in different pH system and UV-VIS spectra from the reduction of purpurate ion obtained in situ by spectro- electrochemistry, it was found that the reduction of purpurate ion is a two electron transfer irreversible process, accompanied with a subsequent chemical reaction at pH<8 in which the reduction product, dibarbituylamine decomposed into uramil and barbituric acid. In addition, the formal potential, E~0′ and electron transfer number, n were calculated from spectra at different potentials. Double potentialstep chronoabsorptometry was employed for measuring the decomposition rate constant of dibarbituylamine. The pseudo-firstorder rate constants at pH4.0, 5.0, 5.5 and 6.4 were 6.6, 5.0, 3.4 and 2.6×10~(-4) s~(-1), respectively.
1987, 3(04): 375-379
doi: 10.3866/PKU.WHXB19870408
Abstract:
Differential heats of adsorption for pyridine on NaY, CaY, R_EY and HY zeoli- tes in the temperature range from ambient temperature to 620 K have been measu- red by a micro-calorimeter. Experimental results show that there are two types of different acidic site in these four Y-zeolites. One type is B-acid site and the other one is non-active L-acid site. Acid strength of B-acid site would increase and non-active L-acid site would decrease as the temperature is raising. Only Na~+ ions act as the non-active L-acid sites on NaY surface and H~+ as the B-acid sites on HY surface for pyridine adsorption, but both B-sites and L-sites present on the surface of R_EY and CaY simultaneously. At higher temperatures the adsorption of pyridine prefers to occur on the strong B-acid sites.
At room temperature the amounts of adsorption for pyridine on these all samples are around 3.0—3.2 mmol g~(-1) which are in accordance with the numbers of the total adsorption sites in super-cages and β-cages.
Differential heats of adsorption for pyridine on NaY, CaY, R_EY and HY zeoli- tes in the temperature range from ambient temperature to 620 K have been measu- red by a micro-calorimeter. Experimental results show that there are two types of different acidic site in these four Y-zeolites. One type is B-acid site and the other one is non-active L-acid site. Acid strength of B-acid site would increase and non-active L-acid site would decrease as the temperature is raising. Only Na~+ ions act as the non-active L-acid sites on NaY surface and H~+ as the B-acid sites on HY surface for pyridine adsorption, but both B-sites and L-sites present on the surface of R_EY and CaY simultaneously. At higher temperatures the adsorption of pyridine prefers to occur on the strong B-acid sites.
At room temperature the amounts of adsorption for pyridine on these all samples are around 3.0—3.2 mmol g~(-1) which are in accordance with the numbers of the total adsorption sites in super-cages and β-cages.
1987, 3(04): 380-384
doi: 10.3866/PKU.WHXB19870409
Abstract:
The evidences for the existence of surface-enhanced Raman Scattering (SERS) active sites in electrochemical systems, both the experimental results and related discussion, have been briefly, reviewed. The irreversible decay (quenching effect) and restoration in SERS intensity of Ag/KCI/piperidine system has been studied by using negative potential pulse and using oxidation-reduction cycle (ORC) treatment applied to silver electrode, respectively, It is found that boehdegcee of both the irreversible intensity decay caused by the potential pulse and the intensity restoration caused by the ORC treatment are almost synchronous for all bands of SERS spectra. Besides, the data given by X-ray photo-electron spectra (XPS) shows that both chloride and piperidine molecules are present on surface of silver electrode which has been immersed in aqueous solution of KCl plus piperidine for several minutes. No detectable SERS signal has been found before ORC treatment. All these results can be interpreted in terms of the concept of surface complexes as SERS active sites existing on the surface of silver eletrode.
The evidences for the existence of surface-enhanced Raman Scattering (SERS) active sites in electrochemical systems, both the experimental results and related discussion, have been briefly, reviewed. The irreversible decay (quenching effect) and restoration in SERS intensity of Ag/KCI/piperidine system has been studied by using negative potential pulse and using oxidation-reduction cycle (ORC) treatment applied to silver electrode, respectively, It is found that boehdegcee of both the irreversible intensity decay caused by the potential pulse and the intensity restoration caused by the ORC treatment are almost synchronous for all bands of SERS spectra. Besides, the data given by X-ray photo-electron spectra (XPS) shows that both chloride and piperidine molecules are present on surface of silver electrode which has been immersed in aqueous solution of KCl plus piperidine for several minutes. No detectable SERS signal has been found before ORC treatment. All these results can be interpreted in terms of the concept of surface complexes as SERS active sites existing on the surface of silver eletrode.
1987, 3(04): 385-388
doi: 10.3866/PKU.WHXB19870410
Abstract:
Using LIF technique, the distribution of rotational temperature of I_2 along the supersonic jet axis has been measured. I_2 was seeded in He, Ar and N_2. Results show that rotational relaxation appears very efficient in jets and Ar and N_2 as car- rier gases are more effective in rotational relaxation than He. The effect of “ve- locity slip” is calculated for I_2 seeded in He and Ar. With He as carrier gas “ve- locity slip” is as large as 360 ms~(-1) compared with 20 ms~(-1) in Ar case, It is pointed out that “velocity slip” would be responsible for the inefficiency He in rotational relaxation of I_2 in our case.
Using LIF technique, the distribution of rotational temperature of I_2 along the supersonic jet axis has been measured. I_2 was seeded in He, Ar and N_2. Results show that rotational relaxation appears very efficient in jets and Ar and N_2 as car- rier gases are more effective in rotational relaxation than He. The effect of “ve- locity slip” is calculated for I_2 seeded in He and Ar. With He as carrier gas “ve- locity slip” is as large as 360 ms~(-1) compared with 20 ms~(-1) in Ar case, It is pointed out that “velocity slip” would be responsible for the inefficiency He in rotational relaxation of I_2 in our case.
1987, 3(04): 389-394
doi: 10.3866/PKU.WHXB19870411
Abstract:
The XPS (X-Ray Photoelectron Spectroscopy), SSIMS (Static Second Ion Mass Spectroscopy) and ISS (Ion Scattering Spectroscopy) have shown that CuCl is dis- persed on γ-Al_2O_3 surface as a monolayer. The maximum amount of dispersion of CuCl on γ-Al_2O_3 surface determined by XPS is approaching to the value determined by XRD.
The binding energy of Cu 2p3/2 obtained by XPS decreases with the amount of CuCl added to the samples. The valence band spectra of CuCl dispersed on γ-Al_2O_3 is different from that of pure CuCl. ISS of He~+ gave a scattering peak of copper of CuCl/γ-Al_2O_3 11 eV higher than that of pure CuCl. They indicate that CuCl has a quite strong interaction with the γ-Al_2O_3 surface. The dispersed CuCl gave a widening Auger peak which can be attributed to the heterogeneity of γ-Al_2O_3 surface.
The XPS (X-Ray Photoelectron Spectroscopy), SSIMS (Static Second Ion Mass Spectroscopy) and ISS (Ion Scattering Spectroscopy) have shown that CuCl is dis- persed on γ-Al_2O_3 surface as a monolayer. The maximum amount of dispersion of CuCl on γ-Al_2O_3 surface determined by XPS is approaching to the value determined by XRD.
The binding energy of Cu 2p3/2 obtained by XPS decreases with the amount of CuCl added to the samples. The valence band spectra of CuCl dispersed on γ-Al_2O_3 is different from that of pure CuCl. ISS of He~+ gave a scattering peak of copper of CuCl/γ-Al_2O_3 11 eV higher than that of pure CuCl. They indicate that CuCl has a quite strong interaction with the γ-Al_2O_3 surface. The dispersed CuCl gave a widening Auger peak which can be attributed to the heterogeneity of γ-Al_2O_3 surface.
1987, 3(04): 395-400
doi: 10.3866/PKU.WHXB19870412
Abstract:
The experimental results at variant programs of raising temperature are care- fully examined during the synthetic process of ZnP_2 while P and Zn are located at the opposite ends of a sealed evacuated quartz tube. It is found that the phosphorus vapour pressure has an effect on zinc phosphorus formation. When the phosphorus vapour pressure is not high enough, Zn_3P_2 will be formed; When the phosphorus vapour pressure is high enough but lower than 4 atm., both red tetra nal ZnP_2 and black monoclinic ZnP_2 will be formed, and the content of blask ZnP_2 is tend to be increasing with the increment of the phosphorus vapour pressure. When the phosphorus vapour pressure is higher than 4 atm., almost 100% black ZnP_2 is formed.
The intermediate product is observed with short-time syhthesis method, and is identified by weight method, chemical analysis and SEM. We have proposed the main mechanism of ZnP_2 synthetic process. During the synthesis of ZnP_2 in a evacuated quartz tube, the ZnP_2 shell can be formed at the surface of the melted Zn. Then the synthetic rate of ZnP_2 mainly depend on volatilizing extent of Zn_3P_2 and ZnP_2 in the shell at high temperature. This mechanism can explaine the fact that the synthesis of ZnP_2 requires sufficient time and that the temperature control at the zinc end has an obvious effect on synthetic rate.
The experimental results at variant programs of raising temperature are care- fully examined during the synthetic process of ZnP_2 while P and Zn are located at the opposite ends of a sealed evacuated quartz tube. It is found that the phosphorus vapour pressure has an effect on zinc phosphorus formation. When the phosphorus vapour pressure is not high enough, Zn_3P_2 will be formed; When the phosphorus vapour pressure is high enough but lower than 4 atm., both red tetra nal ZnP_2 and black monoclinic ZnP_2 will be formed, and the content of blask ZnP_2 is tend to be increasing with the increment of the phosphorus vapour pressure. When the phosphorus vapour pressure is higher than 4 atm., almost 100% black ZnP_2 is formed.
The intermediate product is observed with short-time syhthesis method, and is identified by weight method, chemical analysis and SEM. We have proposed the main mechanism of ZnP_2 synthetic process. During the synthesis of ZnP_2 in a evacuated quartz tube, the ZnP_2 shell can be formed at the surface of the melted Zn. Then the synthetic rate of ZnP_2 mainly depend on volatilizing extent of Zn_3P_2 and ZnP_2 in the shell at high temperature. This mechanism can explaine the fact that the synthesis of ZnP_2 requires sufficient time and that the temperature control at the zinc end has an obvious effect on synthetic rate.
1987, 3(04): 401-406
doi: 10.3866/PKU.WHXB19870413
Abstract:
The photochemistry of n-hexane—TBP binary system under UV irradiation of low pressure mercury lamp has been investigated. It has been found that the excited energy transfer is the main process of energy transfer in this system under γ irradiation by comparing with the results of photo-decomposition. The contribution of subexcited electron in the energy transfer of γ irradiation was discussed.
The photochemistry of n-hexane—TBP binary system under UV irradiation of low pressure mercury lamp has been investigated. It has been found that the excited energy transfer is the main process of energy transfer in this system under γ irradiation by comparing with the results of photo-decomposition. The contribution of subexcited electron in the energy transfer of γ irradiation was discussed.
1987, 3(04): 407-411
doi: 10.3866/PKU.WHXB19870414
Abstract:
CdSe semiconductor thin-film electrodes have been prepared by means of electrodeposition. They are capable of achieving 5.9% solar energy conversion efficiency in PEC performance after being annealed at 450 ℃ in air. Surface photovoltage (SPV) has been used to study their photoelectrochemical properties. SPV spectra of the CdSe thin-films with and without annealing show that surface recombination of minority carriers is significantly reduced after annealing.
The minority carriers diffusion length L_P has been determined by extrapolating the plots ofreciprocal surface photovoltage as a function of the absorption length to zero ΔV~(-1)_(ph). It is found that L_p=0.42 μm.
CdSe semiconductor thin-film electrodes have been prepared by means of electrodeposition. They are capable of achieving 5.9% solar energy conversion efficiency in PEC performance after being annealed at 450 ℃ in air. Surface photovoltage (SPV) has been used to study their photoelectrochemical properties. SPV spectra of the CdSe thin-films with and without annealing show that surface recombination of minority carriers is significantly reduced after annealing.
The minority carriers diffusion length L_P has been determined by extrapolating the plots ofreciprocal surface photovoltage as a function of the absorption length to zero ΔV~(-1)_(ph). It is found that L_p=0.42 μm.
1987, 3(04): 412-417
doi: 10.3866/PKU.WHXB19870415
Abstract:
Active radicals generated during the photochemical hydrogen abstraction bet- ween ethylene tetrachloride and hydrocarbon or alcohol have been studied with the combination of ESR spectroscopy and spin trapping technique, The results show that:
1. CCl_2=CCl and Cl have been formed during the photolysis of CCl_2=CCl_2. Cl further added to C_2Cl_4 to form CCl_3-CCl_2 radical.
2. CCl_2=CCl(or Cl) abstracts hydrogen from methylene group and tertiary carbon of CH_3(CH_2)_nOH(n=3, 7), and (CH_3)_2CH(CH_2)_nOH(n=1,2), to form CH_3-(CH_2)_(n-1)CHOH and (CH_3)_2C(CH_2)_nOH respectively.
3. CCl_2=CCl (or Cl) abstracts hydrogen from methylene group and tertiary carbon of CH_3(CH_2)_nCH_3 (n=3,4,5,6), C_6H_5CH_2CH_3 and (CH_3)_2CH(CH_2)_nCH_3(n=1,4), (C_2H_5)_2CHCH_3, C_6H_5CH(CH_3)_2, to form CH_3(CH_2)_mCH(CH_2)_(n-m-1)CH_3, C_6H_5-CHCH_3 and (CH_3)_2C(CH_2)_nCH_3, (C_2H_5)_2CCH_3, C_6H_5C(CH_3)_2.
Active radicals generated during the photochemical hydrogen abstraction bet- ween ethylene tetrachloride and hydrocarbon or alcohol have been studied with the combination of ESR spectroscopy and spin trapping technique, The results show that:
1. CCl_2=CCl and Cl have been formed during the photolysis of CCl_2=CCl_2. Cl further added to C_2Cl_4 to form CCl_3-CCl_2 radical.
2. CCl_2=CCl(or Cl) abstracts hydrogen from methylene group and tertiary carbon of CH_3(CH_2)_nOH(n=3, 7), and (CH_3)_2CH(CH_2)_nOH(n=1,2), to form CH_3-(CH_2)_(n-1)CHOH and (CH_3)_2C(CH_2)_nOH respectively.
3. CCl_2=CCl (or Cl) abstracts hydrogen from methylene group and tertiary carbon of CH_3(CH_2)_nCH_3 (n=3,4,5,6), C_6H_5CH_2CH_3 and (CH_3)_2CH(CH_2)_nCH_3(n=1,4), (C_2H_5)_2CHCH_3, C_6H_5CH(CH_3)_2, to form CH_3(CH_2)_mCH(CH_2)_(n-m-1)CH_3, C_6H_5-CHCH_3 and (CH_3)_2C(CH_2)_nCH_3, (C_2H_5)_2CCH_3, C_6H_5C(CH_3)_2.
1987, 3(04): 418-424
doi: 10.3866/PKU.WHXB19870416
Abstract:
This paper is the first one about research of the relations between properties and electronic structure for cyclourea nitro-amine compounds by CNDO/2 method, It is found that the stretch vibration frequency (v_(CO)) of carbonyl in their molecules are linearly related with the Mulliken bond order (M_(CO)) of bond C=O and the two-atom energy (E_(CO)) between the C and O atoms, i.e., there are following linear relations:
v_(CO)=-5208+7394M_(CO) r=0.95 (1)
v_(CO)=-6057-4842E_(CO) r=-0.95 (2)
where r is correlation coefficient. Therefore, the position of the characteristic absorptive peak of the carbonyl of the some compounds in this series can be predicted by theoritical calculations and using equation (1) or (2). For example, for 2,4,6,8-tetranitro-semiglycoluril, the predicted ν_(co) values (1813 and 1826 cm~(-1)) are in od agreement with the experimental value (1825 cm~(-1)). According to theoretical analysis and based on results of CNDO/2 computations, it is shown that there exist the approximate linear relationship between the Mulliken bond order (M_(AB)) (from “population analysis”) and the two-atom energy (E_(AB)) (from “energy seperation”) for same type of bond (A—B) in cycloureide nitramine compounds, and it is also shown that M_(AB) is ri rously directly proportional to the resonace integral energy (E~r_(AB)), which is a term included in E_(AB). These indexes obtained by CNDO/2 calculations agree with each other for the measure of the bond strength and the stretch vibration frequency of the carbonyl. Else, the relation between the previous results and the classical review point of the theoritical organic chemistry are also discussed in this paper.
This paper is the first one about research of the relations between properties and electronic structure for cyclourea nitro-amine compounds by CNDO/2 method, It is found that the stretch vibration frequency (v_(CO)) of carbonyl in their molecules are linearly related with the Mulliken bond order (M_(CO)) of bond C=O and the two-atom energy (E_(CO)) between the C and O atoms, i.e., there are following linear relations:
v_(CO)=-5208+7394M_(CO) r=0.95 (1)
v_(CO)=-6057-4842E_(CO) r=-0.95 (2)
where r is correlation coefficient. Therefore, the position of the characteristic absorptive peak of the carbonyl of the some compounds in this series can be predicted by theoritical calculations and using equation (1) or (2). For example, for 2,4,6,8-tetranitro-semiglycoluril, the predicted ν_(co) values (1813 and 1826 cm~(-1)) are in od agreement with the experimental value (1825 cm~(-1)). According to theoretical analysis and based on results of CNDO/2 computations, it is shown that there exist the approximate linear relationship between the Mulliken bond order (M_(AB)) (from “population analysis”) and the two-atom energy (E_(AB)) (from “energy seperation”) for same type of bond (A—B) in cycloureide nitramine compounds, and it is also shown that M_(AB) is ri rously directly proportional to the resonace integral energy (E~r_(AB)), which is a term included in E_(AB). These indexes obtained by CNDO/2 calculations agree with each other for the measure of the bond strength and the stretch vibration frequency of the carbonyl. Else, the relation between the previous results and the classical review point of the theoritical organic chemistry are also discussed in this paper.
1987, 3(04): 425-429
doi: 10.3866/PKU.WHXB19870417
Abstract:
In this paper the electromotive force of following cell: glass electrode |HCl (m)|Cl-ISE has been measured at molalities of HCl solutions from 0.005 to 15 mol kg~(-1) at 25 ℃. We found that Cl~--ISE Nernst's equation isn't followed. The mean activity, coefficients of HCl, calculated according to Nernsts equation are less than 1 in all molality range. On the basis of these facts, chemical adsorption of Cl-ion has been discussed. We belive that in concentrated hydrochloric acid Cl-ion are adsorbed on the surface of Cl-ISE, and form Ag~+-Cl~- and Ag~+-Cl_2~(2-). Potentails of Cl-ISE are determined by following equation: ε=ε°-Slog [γ_±m/(1+K_(γ_±)m)], (K=0.219), The activity coefficients of HCl which, calculated by this equation, are agree with that reported in literature.
In this paper the electromotive force of following cell: glass electrode |HCl (m)|Cl-ISE has been measured at molalities of HCl solutions from 0.005 to 15 mol kg~(-1) at 25 ℃. We found that Cl~--ISE Nernst's equation isn't followed. The mean activity, coefficients of HCl, calculated according to Nernsts equation are less than 1 in all molality range. On the basis of these facts, chemical adsorption of Cl-ion has been discussed. We belive that in concentrated hydrochloric acid Cl-ion are adsorbed on the surface of Cl-ISE, and form Ag~+-Cl~- and Ag~+-Cl_2~(2-). Potentails of Cl-ISE are determined by following equation: ε=ε°-Slog [γ_±m/(1+K_(γ_±)m)], (K=0.219), The activity coefficients of HCl which, calculated by this equation, are agree with that reported in literature.
1987, 3(04): 430-434
doi: 10.3866/PKU.WHXB19870418
Abstract:
We have synthesized the THF-coordinated(1,1′-Trimethylenedicyclopentadienyl) (tert-butyl) lanthanide complex. The ~(13)C NMR spectrum in tetrahydrofuran-d_8 so- lution has been determined and assigned. A theoritical calculation of ~(13)C NMR che- mical shift based on our INDO/σ program has been applied to this compound as the first calculation for lanthanide complex which included f orbitals. The corela- tion between the theoretical calculation results and the experimental data is sati- sfactory.
We have synthesized the THF-coordinated(1,1′-Trimethylenedicyclopentadienyl) (tert-butyl) lanthanide complex. The ~(13)C NMR spectrum in tetrahydrofuran-d_8 so- lution has been determined and assigned. A theoritical calculation of ~(13)C NMR che- mical shift based on our INDO/σ program has been applied to this compound as the first calculation for lanthanide complex which included f orbitals. The corela- tion between the theoretical calculation results and the experimental data is sati- sfactory.
1987, 3(04): 435-439
doi: 10.3866/PKU.WHXB19870419
Abstract:
The liquidus of the Sn-rich range in the phase diagram of Cu-Zn-Sn system has been investigated by means of thermal analysis and X-ray diffraction method. It was found that there are five surfaces corresponding to the primary crystalliza- tion of Sn, η-Cu_6Sn_5, ε-Cu_3Sn, ε-CuZn_(~6), and η-Zn respectively and three invariant points: E, the ternary eutectic point, (90.8 Wt.%Sn, 0.2wt. %Cu; 190 ℃) and two ternary peritectic points P_1(91.3Wt.%Sn, 5.8Wt.%Cu; 358 ℃) and P_2(~0.2 Wt. %Cu, 96.3Wt. %Sn; 218 ℃) in the Sn-rich range. No ternary intermetallic compound was detected.
The liquidus of the Sn-rich range in the phase diagram of Cu-Zn-Sn system has been investigated by means of thermal analysis and X-ray diffraction method. It was found that there are five surfaces corresponding to the primary crystalliza- tion of Sn, η-Cu_6Sn_5, ε-Cu_3Sn, ε-CuZn_(~6), and η-Zn respectively and three invariant points: E, the ternary eutectic point, (90.8 Wt.%Sn, 0.2wt. %Cu; 190 ℃) and two ternary peritectic points P_1(91.3Wt.%Sn, 5.8Wt.%Cu; 358 ℃) and P_2(~0.2 Wt. %Cu, 96.3Wt. %Sn; 218 ℃) in the Sn-rich range. No ternary intermetallic compound was detected.
1987, 3(04): 440-444
doi: 10.3866/PKU.WHXB19870420
Abstract:
We have studied the fluorescence spectra of Coumarin molecules (C47, C311 and C120) in the micelles (C_(12) TAB and C_(16)TAB) and measured the distribution constants K of these systems. It is found that the distrbution constans K change as follows: K_(C47)>K_(C311)>K_(C120) for different molecules in the same micelles and K_(C16TAB)>K_(C12TAB) for the same molecule in different micelles.
We have studied the fluorescence spectra of Coumarin molecules (C47, C311 and C120) in the micelles (C_(12) TAB and C_(16)TAB) and measured the distribution constants K of these systems. It is found that the distrbution constans K change as follows: K_(C47)>K_(C311)>K_(C120) for different molecules in the same micelles and K_(C16TAB)>K_(C12TAB) for the same molecule in different micelles.
1987, 3(04): 445-448
doi: 10.3866/PKU.WHXB19870421
Abstract:
Coal is a very complex system. If the thermal decomposition of the coal is assumed to consist of a large number of various chemical bonds, difference in the strengths of chemical bonds throughout the coal will cause marked differences in the temperatures at which the various bonds rupture. So the activation energy of coal can be viewed as a continuous distribution.
This paper is concerned with the pyrolysis experiments of lean coal and fat coal from Feng-Feng, Heipei province, China.According to the pyrolysis results, the models of activation energies can be obtained for both coals and the most probable activation energies areL E_(lean)=268 kJ mol~(-1), E_(fat)=238 kJ mol~(-1).
Coal is a very complex system. If the thermal decomposition of the coal is assumed to consist of a large number of various chemical bonds, difference in the strengths of chemical bonds throughout the coal will cause marked differences in the temperatures at which the various bonds rupture. So the activation energy of coal can be viewed as a continuous distribution.
This paper is concerned with the pyrolysis experiments of lean coal and fat coal from Feng-Feng, Heipei province, China.According to the pyrolysis results, the models of activation energies can be obtained for both coals and the most probable activation energies areL E_(lean)=268 kJ mol~(-1), E_(fat)=238 kJ mol~(-1).
