Vibrational spectra and force field of terephtalonitrile

The IR and Raman spectra of the two molecules terephtalonitrile and terephtalonitrile-¹⁵N were recorded to permit the general assignment of the vibrational bands observed, in agreement with a D_2h symmetry for these molecules. The general quadratic force field was calculated by the semi-empirical MINDO/3 method from an optimized geometry obtained by the same method. The resulting force field was refined by employing the experimental vibrational frequency data of the two molecules and those of terephtalonitrile-d₄. The final differences between the calculated end experimentally observed frequencies for B_2g and B_3u terephtalonitrile species were within the range ± 0.1 cm⁻¹.     

Vibrational spectra and valence force field calculation of deltic acid

Infrared and Raman spectra of crystalline deltic acid and its deuterated derivative have been studied between 4000 and 20 cm⁻¹. In order to specify vibrational assignment of ring and CO modes based on C_2v molecular symmetry, valence force field calculation was undertaken. It appears that the results obtained for simpler disubstituted cyclopropenones can be applied to deltic acid. So, the highest frequencies about 1930 and 1610 cm⁻¹ involve nearly equal mixture of ring and CO stretching. Two different, strong but asymmetric OH

OC hydrogen bonds occur in crystal.     

Vibrational spectra of benzonitrile-p-d and benzonitrile-d5 and force field of benzonitrile

The i.r. and the Raman spectra of benzonitrile-p-d have been recorded and twenty-three of the fundamental vibrations of benzonitrile-p-d and five of those of benzonitrile-d₅ have been reassigned. A normal coordinate analysis for benzonitrile and its p-d and d₅ derivatives has been carried out. By using a set of valence type force constants, a good fit between the observed and the calculated frequencies has been obtained.     

Vibrational spectra and force field of azacyclic compounds. I. Pyrrole

For the molecules of pyrrole and its symmetric deuterated derivatives, vibrational spectra have been analyzed, and the force field has been defined in natural coordinates.Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 29, No. 5, pp. 651–655, May, 1993.     

Vibrational spectra and molecular force field of N-methylpyridinium ion and some deuterated derivatives

The vibrational spectra of N-methylpyridinium iodide and three of its selectively deuterated derivatives have been recorded in the crystalline as w     

Vibrational spectra and force constants ofS-methyl-N,N-dimethyldithiocarbamate

The IR and Raman spectra ofS-methyl-N,N-dimethyldithiocarbamate were studied in different phase states. The frequencies and vibration modes of normal vibrations were analyzed, and the erroneous assignments made in some previous works were corrected. The force constants of the molecule were estimated using the model of the generalized valenceforce field.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1108–1110, June, 1995.This work was carried out with partial financial support from the International Science Foundation.     

Vibrational spectrum and force field of trimethyl- methoxysilane

The IR and Raman spectra of (CH₃)₃SiOCH₃, (CH₃)₃SiOCD₃, (CD₃)₃SiOCH₃ and (CD₃)₃ SiOCD₃ are presented together with results of normal coordinate calculations. Numerical values of certain force constants and effects of mechanical coupling between Si-O-C bridge vibrations and some of internal vibrations of (CH₃)₃Si and OCH₃ groups are briefly discussed.     

Vibrational spectra of bromobenzene-4-d1 and bromobenzene-2,3,5,6-d4 and force field of bromobenzene

Infrared and Raman spectra of bromobenzene-4-d₁ and bromobenzene-2,3,5,6-d₄ have been recorded in the liquid state, and vibrational assignments have been made by referring to isotope effects and Raman depolarization ratios. The normal coordinate analysis has been carried out for the four isotopic bromobenzenes, −d₀, −d₁, −d₄ and −d₅. The valence force field for benzene and toluene due to La Lau and Snyder has been used with a slight change in off-diagonal terms based on the modified frequency sum rule for symmetry species of isotopic molecules. After least squares refinement of the force field, a good fit between the observed and the calculated frequencies has been obtained, and a close correspondence between the force constants of bromobenzene and those of benzene and toluene has been indicated.     

Vibrational spectra,force fields and electronic structures of sydnones

Normal vibrational analyses of 3-methylsydnone and 3-methylsydnone-d₄ have been performed. On the basis of the set of force constants obtained, the electronic distribution within the mesoionic ring is evaluated and compared to the results of MO calculations. The π-bond order of the sydnone carbonyl group is shown to be lower than that in alicyclic esters and the unusually high “carbonyl stretching” frequency is due to the contributions from other coordinates to this mode. The splitting of the “carbonyl stretching” band observed in the spectra of 3-methylsydnone and of related derivatives is explained by the strong kinematic coupling between mesoionic bonds.     

Vibrational spectra of furan,pyrrole, and thiophene from a density functional theory anharmonic force field

Quartic force fields for furan, pyrrole, and thiophene have been generated using density functional theory (DFT). These were used to evaluate vibrational levels by second-order perturbation theory (PT) and also by the variational method. The results for the fundamental frequencies are in very good agreement with observation. The accuracy of overtones and combination transitions is also good, for those cases where assignments can be made. Second-order PT combines speed and quality whereas the variational approach is inherently more reliable, but converges rather slowly, requiring significant computational effort.     

Vibrational spectra,scaled quantum-mechanical (SQM) force field and assignments for 4H-pyran-4-one

The gas phase i.r. spectrum of 4H-pyran-4-one (hereafter called γ-pyrone) has been recorded in the 4000-400 cm⁻¹ region by a Nicolet 7199 FTIR spectrometer and interpreted using a general valence force field calculated quantum mechanically at the ab initio level with a split-valence 4–21 basis. Assignment of certain fundamentals was facilitated by information gained from the i.r. and Raman spectra of the melt and from the i.r. spectrum of the saturated solution in CCl₄.To account for systematic computational errors, the theoretical ab initio force field was scaled using a set of constants derived by the empirical fitting of force fields computed for related molecules to their observed spectra. Either the scale factors derived for a family of open-chain molecules or, better, for benzene could be used to yield a scaled force field which gave unequivocal assignments for γ-pyrone. The method promises to be of general applicability for molecules of this complexity.     

Metallomethanes: XII. Vibrational spectra and force fields of methylmercurimethanes

The vibrational spectra data, the assignments, and the results of normal coordinate calculations for CH_{4 − n}(HgCH₃)_n molecules (2 ⩽ n ⩽ 4) are reported. The central CHg valence force constants are 1.870, 1.653, and 1.582 N cm⁻¹ while the terminal ones are 2.121, 2,101, and 2.160 N cm⁻¹ for n = 2, 3 and 4, respectively. The latter values are 12, 21, and 27% higher than the central CHg force constants, but all of them are substantially lower than those in dimethylmercury (2.379 N cm⁻¹). These findings can be accounted for in terms of increasing shift of electron density towards the periphery of these molecules and increasing non-bonded metal-metal interaction. The nature of the normal modes is discussed.     

Metallomethanes: XIII. Vibrational spectra and force fields of cyanomercuriomethanes

Vibrational spectra with assignments and results of normal coordinate calculations for cyanomercuriomethanes CH_4−n(HgCN)_n (2 ≤ n ≤ 4) are discussed. The valence force constants of the central CHg bonds are 2.149, 1.944, and 1.798 N cm⁻¹,while those of the HgCN bonds are 2.204, 2.123, and 2.162 N cm⁻¹, for n = 2, 3 and 4, respectively. All these force constants are lower than the corresponding constants for methylmercury cyanide (2.445 and 2.379 N cm⁻¹). The overall behaviour of these force constants as a function of the degree of mercuration n is quite similar in both the cyanomercuriomethanes CH_4−n(HgCN) and methylmercuriomethanes CH_4−n(HgCH₃)_n series with the difference that there are variations in the constants at higher values in the former series. The potential energy distributions indicate that the valence vibrations of the CH, CN, and HgCN bonds are almost independent of all other vibrations, which in turn are more or less strongly coupled.     

Vibrational spectra of stannane: Harmonic force field, Raman and IR intensities from ab initio correlated wavefunctions

The vibrational spectra and the harmonic force field for the stannane molecule has been calculated from ab initio SCF calculations using an effective core potential and two double-zeta basis sets for the valence electrons. Polarized functions and electron correlation effects on the calculated force constants and frequencies are analyzed carefully. At HF SCF level the calculated frequencies are higher than the experimental ones by about 8.15% while at second-order Møller-Plesset perturbation level, the mean absolute percentage deviation of the frequencies is found to be 3.75%. This mean absolute percentage deviation is notably improved at SDCI (3.2%) and SDQCI (2.2%) levels of theory. The integrated molar absorption coefficients and the scattering activities are calculated and their values agree reasonably with experiment.