Theoretical interpretation of the vibrational spectra of methyl-substitutedS-triazine

The problems of normal vibrations of mono-, di-, and trimethyl-substituted S-triazine are solved. Assignments of the frequencies of fundamental vibrations for an aromatic ring and methyl groups are suggested. Corrections for methyl substitution for the force constants of S-triazine are determined. The groups of characteristic and noncharacteristic vibrations of the aromatic ring of S-triazine on substitution of hydrogen are established. Saratov State University, 83, Astrakhanskaya St., Saratov, 410601, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 65, No. 3, pp. 322–325, May–June, 1998.     

Theoretical analysis of vibrational spectra of tautomeric purine forms

A theoretical analysis of vibrational spectra of purine tautomers was carried out using the DFT/B3LYP/6-31G(d)* method. The influence of intermolecular interaction in purine dimers was estimated. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 1, pp. 23–27, January–February, 2008.     

Calculation and interpretation of vibrational spectra of halogen-substituted ethanes

The frequencies, forms of the normal vibrations, and the potential energy constants of the CH₃CHF₂, CH₃CHCl₂, and CH₃CHBr₂ molecules were calculated. The interpretation of the vibrational spectra existing in the literature was refined, and the characteristics of the force field in these molecules were established.     

Calculation and interpretation of vibrational spectra of monomethyl-substituted pyridines

A calculation of the fundamental frequencies of antisymmetric vibrations of -, -, and -picolines and -picoline-D₇ is made. The calculated values show good agreement with experimental vibrational-spectral data. The effect of methyl substitution on the nonplanar-vibration frequency of pyridine is explained.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 114–119, February, 1972.The authors thank N. K. Siderov and M. L. Kats for their interest.     

Theoretical prediction of vibrational spectra: The out-of-plane force field and vibrational spectra of pyridine

The harmonic force field for the out-of-plane vibrations of pyridine has been calculated from ab initio Hartree-Fock wavefunctions obtained with a 4–21 basis set of contracted Gaussians. To account for systematic errors, the calculated force constants were scaled, using only two independent sclae factors which were transferred unchanged from benzene. The resulting scaled quantum mechanical force field, which is strictly a priori in that it is not based on any experimental data on pyridine, predicts the 64 out-of-plane fundamental frequencies of pyridine and its deuterated isotopomers of C_2v symmetry with a mean deviation from experiment of only 8.5 cm^?1. Addition of polarization functions to the basis set for the nitrogen atom and refinement of the two scale factors by fitting them to the observed pyridine spectra produce no significant improvement in the fit. Assignments of the vibrational spectra are discussed.     

几种全氟烷基碘化物分子振动光谱的理论研究

采用分子轨道从头算方法,分别在HF、MP2和B3LYP水平下对三种全氟烷基碘化物分子CF3I、C2F5I和n-C3F7I的振动红外光谱和喇曼光谱进行理论计算,给出了各频率所对应的振动模式对称性、红外谱线相对强度及喇曼活性。结合计算值和实验值对三种全氟烷基碘化物分子的振动光谱进行了讨论,结果表明理论计算值与实验观测值吻合得很好。