On the normal vibrations of nonrigid molecule B(CH3)3

Treating the symmetry operations as transformations in higher dimensional space, it is shown that Wigner’s method can be straightaway extended to study the vibrations of nonrigid molecules exhibiting free or nearly free internal rotations. The molecule B(CH₃)₃ is illustrated.     

CH(CH3)3 的耦合CH伸缩和弯曲振动的纠缠

以不同的多极量子数和初态,我们用约化的线性熵研究CH(CH3)3 的耦合CH伸缩和弯曲振动的动力学纠缠,结果表明：在多极量子数大于等于３时,态|0,2N>的最大纠缠能在较短的时间内得到;态|N,0>的纠缠振荡频率比态|0,2N>的要小,而振荡的幅度要大．     

CH3CH2O及CH3CHOH与HO2反应机理的理论研究

采用CCSD(T)/cc-pVTZ//B3LYP/6-311++G(2df,2p)水平上对CH3CHOH + HO2和CH3CH2O + HO2反应体系的单、三重态反应机理进行了详细的理论研究.计算结果表明,CH3CHOH + HO2反应主要发生在单重态势能面上,其中四条通道均为快速自发过程;CH3CH2O + HO2反应在三重态势能面上的通道CH3CH2O + HO2 → 3IM11 → 3TS11 → P11 (CH3CH2OH + 3O2)为动力学和热力学的优势路径. 大气中CH3CHOH比CH3CH2O更容易稳定存在.     

CH3CH2O及CH3CHOH与HO2反应机理的理论研究

采用CCSD(T)/cc-pVTZ//B3LYP/6-311++G(2df,2p)水平上对CH3CHOH + HO2和CH3CH2O + HO2反应体系的单、三重态反应机理进行了详细的理论研究.计算结果表明,CH3CHOH + HO2反应主要发生在单重态势能面上,其中四条通道均为快速自发过程;CH3CH2O + HO2反应在三重态势能面上的通道CH3CH2O + HO2 → 3IM11 → 3TS11 → P11 (CH3CH2OH + 3O2)为动力学和热力学的优势路径. 大气中CH3CHOH比CH3CH2O更容易稳定存在.     

CH_3CH_2O及CH_3CHOH与HO_2反应机理的理论研究

采用CCSD(T)/cc-p VTZ//B3LYP/6-311++G(2df,2p)水平上对CH_3CHOH+HO_2和CH_3CH_2O+HO_2反应体系的单、三重态反应机理进行了详细的理论研究.计算结果表明,CH_3CHOH+HO_2反应主要发生在单重态势能面上,其中四条通道均为快速自发过程;CH_3CH_2O+HO_2反应在三重态势能面上的通道CH_3CH_2O+HO_2→~3IM11→~3TS11→P11(CH_3CH_2OH+~3O_2)为动力学和热力学的优势路径.大气中CH_3CHOH比CH_3CH_2O更容易稳定存在.     

Ab initio calculations and vibrational spectra of CH3SC=CH and CH3SC=CSCH3

Methylthio-(MTE) and bis-methylthioethyne (BMTE) molecules are calculated by the SCF MO method (geometry optimization, basis set 6–31G*/MP2). The calculated internal rotation barriers of methyl groups are 7.12 kJ/mole for MTE and 12.86 kJ/mole for BMTE (both groups are simultaneously rotated). The s-gosh-orientation of the thiomethyl fragments corresponds to a stable conformation of BMTE. The estimated values of the s-cis- and s-trans-barriers of mutual rotation of SCH₃ groups about the axis of the C=C bond are 13.61 and 12.54 kJ/mole, respectively. Conformationally sensitive MOs and vibration frequencies are established. An analysis of the experimental IR absorption and Raman spectra and the calculated vibrational spectrum makes it possible to conclude that in the liquid phase the BMTE molecules also have an s-gosh-conformation. Translated from ZhurnalStrukturnoi Khimii, Vol. 39, No. 4, pp. 602–609, July–August, 1998.     

Infrared-microwave two-photon spectra of the ν3 bands of 12CH3F and 13CH3F

Infrared-microwave two-photon spectra have been obtained for the ν₃ bands of ¹²CH₃F and ¹³CH₃F with a two-photon spectrometer employing a CO₂ laser and a computer-coupled microwave source operating in the 8–18 GHz region. Even though the intensities of the spectra for the double parity levels in these molecules are inversely proportional to the square of the microwave frequency, transitions have been observed with microwave frequencies of up to 16 GHz. Comparison of these observed two-photon frequencies to frequencies predicted from infrared laser Stark spectroscopy, and to frequencies calculated from vibration-rotation parameters obtained by fitting these and other frequencies, shows agreement to within a few MHz. Spectroscopic parameters for the ground and ν₃ excited states of the two species are reported.     

Normal vibrations of SrTiO3 lattice

The model of polarizable ions was used to calculate the frequencies and amplitudes of normal transverse modes of vibration (for=0) of an SrTiO₃ lattice and their temperature dependence due to the temperature dilatation of lattice. In agreement with Cochran's theory, one of the frequencies was chosen equal to zero in the assumed Curie point of 28°K. This can be done by reducing the charges of the ions by the factor 0.278. The temperature dependence of the lowest frequency is in qualitative agreement both with Cochran's assumptions and with the measurements of Cowley. A fundamental role in the character of its dependence and thus in the ferroelectric behaviour of the material is played by the long-range Coulomb forces. The series of experimental data on the values of normal frequencies, the lattice constant and elastic constants indicate a decrease in the values used for the overlap energy constants. The large reduction in the charges (necessary for frequencies aboveT _C to be real) show, however, that the model of polarizable ions is unsuitable for explaining the properties of SrTiO₃.The authors would like to thank V. Janovec C. Sc. and V. Dvoák C. Sc. for guiding the work, valuable discussions and advice, which helped to improve the work. They are also indebted to J. Fousek C. Sc. for a number of valuable remarks, and thank H. Dvoáková and E. Víchová for carefully performing some of the numerical calculations.     

CH3S CH2SH异化反应的理论研究

利用密度泛函理论(DFT)和从头算(ab initio)研究了CH3S←→CH2SH互异化的反应机理．采用HF、B3LYP、MP2理论水平和中等基组6-31(d)，计算了CH3S、CH2SH及其过渡态的结构参数、谐振频率、零点能(ZPF)、总能量和相对能量，并利用B3LYP／6-31(d)的方法计算了反应的内禀反应坐标(IRC)，给出了分子构型和自旋污染沿反应坐标的变化曲线，以及最小能量曲线(MEP)、绝热能量曲线．此外，利用传统过渡态理论(CTST)研究了该互异化反应的速率常数和平衡常数在200～1000K的变化．     

CH3CH2+O(3P)反应机理的理论研究

利用abinitio方法对CH3CH2+O(3P)反应进行了理论研究,在MP2/6311+G(d,p)水平上优化得到了反应途径上的反应物、中间体、过渡态和产物的几何构型和谐振频率,并在QCISD(T)/6311+G(d,p)水平上进行单点能计算.计算结果表明:CH2O+CH3、CH3CHO+H和CH2CH2+OH是主要反应产物,其中CH2O+CH3主要来自反应通道A1:(R)→IM1→TS3→(A),CH3CHO+H主要来自反应通道B1:(R)→IM1→TS4→(B),CH2CH2+OH主要来自直接抽提反应通道C1和C2:(R)→TS1(TS2)→(C).计算结果同时表明该反应生成CO的通道能垒是非常高的,CO应该不是主要产物.     

Molecular constants of SiH3C ≡ CH and SiD3C ≡ CH

A normal co-ordinate analysis of silylacetylene and silylacetylene-d ₃ has been carried out following Wilson'sF-G matrix method. The potential energy constants obtained therefrom have been used to evaluate rotational distortion constants and mean square amplitudes of vibration for these molecules. Thermodynamic functions, such as heat content, free energy, entropy heat capacity for the ideal gaseous state at one atmosphere pressure and with the usual rigid rotor harmonic oscillator approximation, have also been calculated for 12 temperatures from 100°K to 1000°K.     

3.508 μ-HeXe-laser line absorption by CH3COOCH3, CH3, and NO2 and infrared emission at 6.89 μ by CH3COOCH3 and CH3 at elevated temperatures

Shock-tube HeXe-laser absorption data at ω_L=2850.633 cm^-1 for CH₃COOCH₃ at 757≤T, °K≤1344, NO₂at 412≤T, °K≤1859, andCH₃at 1283≤T, °K≤1562 are presented. Approximate models are used for the effective spectral absorption coefficient of vibration-rotation lines for analytical representations of the results around atmospheric pressures. For CH₃COOCH₃, an equivalent Voigt-profile for an isolated line was adopted in order to account for a dependence on total pressure of the laser absorption coefficient. Shock-tube emission data at λ=6.890 μ(Δλ=0.197μ) forCH₃COOCH₃at 814≤T, °K≤1651 and for CH₃at 1377≤T, °K≤1562 in the v₄-fundamental of the H-bond bending mode of the CH₃-group are well described at atmospheric pressures by approximations of just-overlapping-line models for polyatomic molecules. The adopted models are useful for concentration-time history measurements of methyl acetate, nitrogen dioxide, and methyl radicals behind shock waves.     

Structures and thermochemistry of methyl ethyl sulfide and its hydroperoxides: HOOCH2SCH2CH3, CH3SCH(OOH)CH3, CH3SCH2CH2OOH,and radicals

Hydroperoxides and the corresponding peroxy radicals are important intermediates during the partial oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃) in both atmospheric chemistry and in combustion. Structural parameters, internal rotor potentials, bond dissociation energies, and thermochemical properties (ΔH_f^o, S^o and C_p(T)) of 3 corresponding hydroperoxides CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, CH₃SCH₂CH₂OOH of methyl ethyl sulfides, and the radicals formed via loss of a hydrogen atom are important to understanding the oxidation reactions of MES. The lowest energy molecular structures were identified using the density functional B3LYP/6‐311G(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods. Isodesmic reactions were used to determine ?H_f^o values. Internal rotation potential energy diagrams and rotation barriers were investigated using the B3LYP/6‐31G(d,p) level theory. Contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation based on the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CH_2, CH₂(OOH)SCH₂CH₃, CH₃SCH(OOH)CH₃, and CH₃SCH₂CH₂OOH are ?14.0, ?33.0, ?37.2, and ?32.7 kcal/mol, respectively. Group additivity values were developed for estimating properties of structurally similar and larger sulfur‐containing peroxides. Groups for use in group additivity estimation of sulfur peroxide thermochemical properties were developed.     

Structural and thermochemical studies on CH3SCH2CHO,CH3CH2SCHO,CH3SC(═O)CH3, and radicals corresponding to loss of H atom

CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are intermediates during the partial oxidation of CH₃SCH₂CH₃ in the atmosphere and in combustion processes. Thermochemical properties (ΔH_f^o, S^o and C_p(T)), structures, internal rotor potentials, and C─H bond dissociation energies of the parent molecules and their radicals formed after loss of a hydrogen atom are of value in understanding the oxidation processes of methyl ethyl sulfide. The lowest energy molecular structures were initially determined using the density functional B3LYP/6‐311G/(2d,d,p) level of theory. Standard enthalpies of formation (ΔH_f^o₂₉₈) for the radicals and their parent molecules were calculated using the density functional B3LYP/6‐31G(d,p), B3LYP/6‐31 + G(2d,p), and the composite CBS‐QB3 ab initio methods using isodesmic reactions. Internal rotation potential energy diagrams and internal rotation barriers were investigated using B3LYP/6‐31 + G(d,p) level calculations. The contributions for S^o₂₉₈ and C_p(T) were calculated using the rigid rotor harmonic oscillator approximation on the basis of the structures and vibrational frequencies obtained by the density functional calculations, with contributions from torsion frequencies replaced by internal rotor contributions from the method of Pitzer‐Gwinn. The recommended values for enthalpies of formation of the most stable conformers of CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ are ?34.6 ± 0.8, ?42.4 ± 1.2, and ‐49.7 ± 0.8 kcal/mol, respectively. The structural and thermochemical data presented for CH₃SCH₂CHO, CH₃CH₂SCHO, and CH₃SC(═O)CH₃ and their radicals are of value in understanding the mechanism and kinetics of methyl ethyl sulfide oxidation under varied temperatures and pressures. Group additivity values are developed for estimating properties of structurally similar, larger sulfur‐containing compounds.     

Doppler-limited spectra of the ν3 vibration of 12CH4 and 13CH4

The tetrahedral splittings in the P and R branches of the ν₃ band of natural methane have been examined with Doppler-limited resolution using a difference-frequency spectrometer. The spectra obtained by this difference-frequency mixer are compared to recent high-resolution grating spectrometer studies of ¹²CH₄ and enriched ¹³CH₄. The resolution, selectivity and precision are improved over the conventional methods. The mixing spectrometer utilizes tunable, narrow linewidth infrared radiation generated in the nonlinear optical crystal, LiNbO₃ as the beat frequency between a CW argon ion and a tunable dye laser. This spectrometer covers the 2.2 to 4.2 μm infrared spectrum with an instrumental resolution of 5 × 10^?4 cm^?1 and continuous scans up to ～1 cm^?1 and with ir power ～1 μW.