DFT and AM1 methods were used to study the reaction of OH radical with hexachlorobenzene(HCB). The optimized structures of the reactants, the products and the transition states were found. A reasonable reaction path w...DFT and AM1 methods were used to study the reaction of OH radical with hexachlorobenzene(HCB). The optimized structures of the reactants, the products and the transition states were found. A reasonable reaction path was determined through IRC calculations. The activation energy obtained is in good agreement to the experimental value.展开更多
Criegee intermediate is believed to play an important role in the atmospheric chemistry.Because of its short life and the difficulty in experimental study, we carried out ah initio calculations on the thermochemistry ...Criegee intermediate is believed to play an important role in the atmospheric chemistry.Because of its short life and the difficulty in experimental study, we carried out ah initio calculations on the thermochemistry of the Criegee involving reactions in this study. Thermochemistrydata of reaction enthalpies and Gibbs free energies for four different stable structures of the Criegeeintermediates (singlet CH2OO ①1 A1 in C2v, triplet CH2OO ②3B1 in C2v, singlet CH2OO ③1A’ in Cs and triplet CH2OO ④ in C1 symmetry) involved in some of the gas-phase reactions were calculated at the standard Gaussian-2 [G2(MP2) and G2] and a modified G2, G2(fu1)[10],levels of theory. Relative energies among those Criegees and formic acid were compared. Chemical reactions incltlde the formation of Criegees, re-arrangement from Criegee to formic acid, dissociations (producing CH2(3B1)+O2, CH2(1A1)+O2, CO2+H2, CO2+2H, CO+H2O, OH+HCO) andthe reactions between Criegee and NO/H2O. Standard equilibrium constants for some reactions were investigated and may be obtained for all of the rest reactions involved in this study by the standard Gibbs free energies. It is shown that the formation of Criegee①-④ by ethylene and ozone, the re-arrangement from any Criegee to formic acid, the dissociation in producing CO2+O2and CO+H2O and the reactions between any Criegee and NO/H2O are all favourable thermodynamicaly. The dissociation in forming CO2+2H and OH+HCO is less favourable. While the dissociation in forming carbene (either in 3B1 or 1A1 state) is not allowed by values. Standard enthalpies of formation at 298 K for the four Criegees were predicted at the G2(ful) level of theory. Each value is the average value from ten of the above reactions and they are -4.3, 74.8,98.9 and 244.6 kJ mol-1 at the G2(ful) level for Criegee ① to Criegee ④, respectively. In addition, tile standard enthalpy of formation at 298 K for HOCH2OOH is further predicted to be -315.6 kJ mol-1 at the G2(MP2) level.展开更多
A general method in considering the core electromc correlation energies has been proposed and introduced into the standard Gaussian-2 (G2)[7] theory hy small post-Hartree-Fock calculations. In this papcr an additional...A general method in considering the core electromc correlation energies has been proposed and introduced into the standard Gaussian-2 (G2)[7] theory hy small post-Hartree-Fock calculations. In this papcr an additional MP2(FC)/6-31G(d) calculation over the G2 procedures is employed and examined in modihcation in modification to the flaw of Frozen-Core (FC) approximation of G2 vai eq:E(full)= E[MP2(full)/6-31G(d)]-E[MP2(FC)/6-31G(d)]where the MP2(full)/6-31G(d) cnergy has been obtaincd in the molefular gcometry optimizations. This energy, E(full), is directly added into the total G2 energy of a molecule in facilitating the effect of core electronic correlations for each molecule in chemical reactions. It has been shown that the over-all avcrage absolute deviation for the 125 reaction energies of the G2 test set (test set 1) is slightly reduced from 5.09 to 5.01 kJ, mol(-1) while for the 55 D0 values, which have been used for the derivation of the A coefficient of the empirical High-Level-Correction (HLC), it is also reduced from 4.99 [for both G2 and G2(COMPLETE)[8]]to 4.77 kJ, mol(-1). In addition, Iargcr crrors (greater than ±8.4 kJ. mol(-1) for the D0 energies are improved, especially for the largest error of the D0of SO2 This error is reduced from 21.3 to 15.4 kJ. mol(-1), in which the experimental geometry would further reduce it by 7.1kJ.mol(-1)[8].Another improvement is the absolute value of the A coefficient in HLC being reduced from 4.81 for G2 to 4.34 milli-hartrees which is believed to be useful in isolating the relationship between the HLC and the FC approximation.Modifications to the original G2 from this work is denoted as G2(fu 1) and thus the G2 (fu 1) total energy for a molecule isE[G2(fu 1)]= E[G2]+ E(full)with a new E[HLC] =0.19α- 4.34nβ milli-hartree.展开更多
A recent experimental dtermination[1] of the dissociation energies (Do) for H2N-H, H2N+-H and H2N-H+, the ionization energies for NH3 and NH2 resulted inlarge deviations when compared with those of the earlier values ...A recent experimental dtermination[1] of the dissociation energies (Do) for H2N-H, H2N+-H and H2N-H+, the ionization energies for NH3 and NH2 resulted inlarge deviations when compared with those of the earlier values and the QCISD(T)/6-311+G(3df,2p) ab initio calculations. We have performed some higher level ab initio calculations on these data by utilizing the Gaussian 92/DFT and Gaussian 94 pakages of programs and have assessed the available experhaental values. Our calculations were carried out at the QCISD (TQ)/aug-cc-pVDZ, G2(QCI), QCISD(T)/6-311 ++G(3df,3p(1)and QCISD(T)/aug-cc-pVTZ levels of theory. Geometries were optimized at both of the MP2(full)/6-31G(d) and the MP2(full)/6-31(d,p) levels, and were compared with those of the expcriments if available. The MP2(full)/6-31G(d,p) tight-optimized geometries for the neutrals are closer to those of the experiments than those of th.MP2 (full)/6-31G(d), and are in excellent agreoment with the experimental results as shown in Table 1. In this case,we assumed that the optimized geometries for the cations would be better if p polarization functions are added to the hydrogen atoms. We firstly noted that the sym-mtry of the NH3+ cation was D3h, other than Cs. as reported in ref.[1]. All of the zero-point energies and the final geometries are calculated at the MP2(full)/6-31G(d,p) level of theory- We have also repeated the QCIS D(T )/6-311 + G(3df,2p) calculations of ref. [1], because we could not identify their level of goemetry optithezation.It is found that the total energy, -55.244 19 Hartrees, for NH (1A1 ) in ref.[1] might be in error. Our result is -55.336 29 Hartrees at the same level of theory. At our highest level [QCISD(T)/aug-cc-pVTZ] of calculations as shown in Table 3, the D0, (temperature at zero Kelvin) values of H2N-H, H:N+-H(3B1for NH2+ ) and H2N- H+ are 4.51, 5.49 and 8.00 eV. respectively. These data reported in re f.[1] were 4.97, 5.59 and 8.41 eV, respectively. Our result on Do(H2N-H) supports the work of ref.[2,3,5,6]. The ionization energies (IE) for NH3 and NH2 (3B1 for NH) at ou-r highest level are 10.11 and 11.09 eV while in ref[1] were 10.16 and 10.78 eV, respectively.For the latter, our result supports the eXperforent of ref.[3]. Our predicted Do for HNt-H and IE for NH2 (1A1 for each NH) are 6.80 and 12.39 eV, respectively. These values dther greatly from the predicted values (9.29 and 14.88 eV) of ref.[1] where the total energy of NHt(1A1) Anght be in error. The Do value for HN-H has not been found in re f.[1]. Our result supports the work of ref.[3]. We have also derived all of these values at the temperatu-re of 298K and under the pressure of 101kPa at several levels of thoery as shown in Table 3. On examining the experiment of re f.[1] in detail, it is easy to find that all of the larger deviations ndght be from a too high value of the appearance potential of proton AP(H+). Indeed, ref.[1] has mentioned that the detendntion of AP(H+), due to kinetic shift, would lead to a hihger value for the dissociation energy as has been pointed out by Berkowitz and Ruscic. In this work, we concluded that, besides some ndstakes in the theoretical calculations of ref.[1], the dissociation energies for H2N-H and H2N-H+,the IE for NH2 (3B1 for NH) ndght also be unreliable and need to be re-examined.展开更多
文摘DFT and AM1 methods were used to study the reaction of OH radical with hexachlorobenzene(HCB). The optimized structures of the reactants, the products and the transition states were found. A reasonable reaction path was determined through IRC calculations. The activation energy obtained is in good agreement to the experimental value.
文摘Criegee intermediate is believed to play an important role in the atmospheric chemistry.Because of its short life and the difficulty in experimental study, we carried out ah initio calculations on the thermochemistry of the Criegee involving reactions in this study. Thermochemistrydata of reaction enthalpies and Gibbs free energies for four different stable structures of the Criegeeintermediates (singlet CH2OO ①1 A1 in C2v, triplet CH2OO ②3B1 in C2v, singlet CH2OO ③1A’ in Cs and triplet CH2OO ④ in C1 symmetry) involved in some of the gas-phase reactions were calculated at the standard Gaussian-2 [G2(MP2) and G2] and a modified G2, G2(fu1)[10],levels of theory. Relative energies among those Criegees and formic acid were compared. Chemical reactions incltlde the formation of Criegees, re-arrangement from Criegee to formic acid, dissociations (producing CH2(3B1)+O2, CH2(1A1)+O2, CO2+H2, CO2+2H, CO+H2O, OH+HCO) andthe reactions between Criegee and NO/H2O. Standard equilibrium constants for some reactions were investigated and may be obtained for all of the rest reactions involved in this study by the standard Gibbs free energies. It is shown that the formation of Criegee①-④ by ethylene and ozone, the re-arrangement from any Criegee to formic acid, the dissociation in producing CO2+O2and CO+H2O and the reactions between any Criegee and NO/H2O are all favourable thermodynamicaly. The dissociation in forming CO2+2H and OH+HCO is less favourable. While the dissociation in forming carbene (either in 3B1 or 1A1 state) is not allowed by values. Standard enthalpies of formation at 298 K for the four Criegees were predicted at the G2(ful) level of theory. Each value is the average value from ten of the above reactions and they are -4.3, 74.8,98.9 and 244.6 kJ mol-1 at the G2(ful) level for Criegee ① to Criegee ④, respectively. In addition, tile standard enthalpy of formation at 298 K for HOCH2OOH is further predicted to be -315.6 kJ mol-1 at the G2(MP2) level.
文摘A general method in considering the core electromc correlation energies has been proposed and introduced into the standard Gaussian-2 (G2)[7] theory hy small post-Hartree-Fock calculations. In this papcr an additional MP2(FC)/6-31G(d) calculation over the G2 procedures is employed and examined in modihcation in modification to the flaw of Frozen-Core (FC) approximation of G2 vai eq:E(full)= E[MP2(full)/6-31G(d)]-E[MP2(FC)/6-31G(d)]where the MP2(full)/6-31G(d) cnergy has been obtaincd in the molefular gcometry optimizations. This energy, E(full), is directly added into the total G2 energy of a molecule in facilitating the effect of core electronic correlations for each molecule in chemical reactions. It has been shown that the over-all avcrage absolute deviation for the 125 reaction energies of the G2 test set (test set 1) is slightly reduced from 5.09 to 5.01 kJ, mol(-1) while for the 55 D0 values, which have been used for the derivation of the A coefficient of the empirical High-Level-Correction (HLC), it is also reduced from 4.99 [for both G2 and G2(COMPLETE)[8]]to 4.77 kJ, mol(-1). In addition, Iargcr crrors (greater than ±8.4 kJ. mol(-1) for the D0 energies are improved, especially for the largest error of the D0of SO2 This error is reduced from 21.3 to 15.4 kJ. mol(-1), in which the experimental geometry would further reduce it by 7.1kJ.mol(-1)[8].Another improvement is the absolute value of the A coefficient in HLC being reduced from 4.81 for G2 to 4.34 milli-hartrees which is believed to be useful in isolating the relationship between the HLC and the FC approximation.Modifications to the original G2 from this work is denoted as G2(fu 1) and thus the G2 (fu 1) total energy for a molecule isE[G2(fu 1)]= E[G2]+ E(full)with a new E[HLC] =0.19α- 4.34nβ milli-hartree.
文摘A recent experimental dtermination[1] of the dissociation energies (Do) for H2N-H, H2N+-H and H2N-H+, the ionization energies for NH3 and NH2 resulted inlarge deviations when compared with those of the earlier values and the QCISD(T)/6-311+G(3df,2p) ab initio calculations. We have performed some higher level ab initio calculations on these data by utilizing the Gaussian 92/DFT and Gaussian 94 pakages of programs and have assessed the available experhaental values. Our calculations were carried out at the QCISD (TQ)/aug-cc-pVDZ, G2(QCI), QCISD(T)/6-311 ++G(3df,3p(1)and QCISD(T)/aug-cc-pVTZ levels of theory. Geometries were optimized at both of the MP2(full)/6-31G(d) and the MP2(full)/6-31(d,p) levels, and were compared with those of the expcriments if available. The MP2(full)/6-31G(d,p) tight-optimized geometries for the neutrals are closer to those of the experiments than those of th.MP2 (full)/6-31G(d), and are in excellent agreoment with the experimental results as shown in Table 1. In this case,we assumed that the optimized geometries for the cations would be better if p polarization functions are added to the hydrogen atoms. We firstly noted that the sym-mtry of the NH3+ cation was D3h, other than Cs. as reported in ref.[1]. All of the zero-point energies and the final geometries are calculated at the MP2(full)/6-31G(d,p) level of theory- We have also repeated the QCIS D(T )/6-311 + G(3df,2p) calculations of ref. [1], because we could not identify their level of goemetry optithezation.It is found that the total energy, -55.244 19 Hartrees, for NH (1A1 ) in ref.[1] might be in error. Our result is -55.336 29 Hartrees at the same level of theory. At our highest level [QCISD(T)/aug-cc-pVTZ] of calculations as shown in Table 3, the D0, (temperature at zero Kelvin) values of H2N-H, H:N+-H(3B1for NH2+ ) and H2N- H+ are 4.51, 5.49 and 8.00 eV. respectively. These data reported in re f.[1] were 4.97, 5.59 and 8.41 eV, respectively. Our result on Do(H2N-H) supports the work of ref.[2,3,5,6]. The ionization energies (IE) for NH3 and NH2 (3B1 for NH) at ou-r highest level are 10.11 and 11.09 eV while in ref[1] were 10.16 and 10.78 eV, respectively.For the latter, our result supports the eXperforent of ref.[3]. Our predicted Do for HNt-H and IE for NH2 (1A1 for each NH) are 6.80 and 12.39 eV, respectively. These values dther greatly from the predicted values (9.29 and 14.88 eV) of ref.[1] where the total energy of NHt(1A1) Anght be in error. The Do value for HN-H has not been found in re f.[1]. Our result supports the work of ref.[3]. We have also derived all of these values at the temperatu-re of 298K and under the pressure of 101kPa at several levels of thoery as shown in Table 3. On examining the experiment of re f.[1] in detail, it is easy to find that all of the larger deviations ndght be from a too high value of the appearance potential of proton AP(H+). Indeed, ref.[1] has mentioned that the detendntion of AP(H+), due to kinetic shift, would lead to a hihger value for the dissociation energy as has been pointed out by Berkowitz and Ruscic. In this work, we concluded that, besides some ndstakes in the theoretical calculations of ref.[1], the dissociation energies for H2N-H and H2N-H+,the IE for NH2 (3B1 for NH) ndght also be unreliable and need to be re-examined.
