Molecular vibrational constants of some simple polyatomic molecules. Methyl,silyl, and germyl halides

The force constants and compliance constants of methyl, silyl, and germyl fluoride, chloride, bromide, and iodide have been calculated by the iterative consistency method. Using the force fields so obtained, centrifugal distortion constants, Coriolis coupling constants, and mean amplitudes of vibration have been computed and compared with experimental data, where available.     

Harmonic force fields and mean amplitudes of vibration for some molecules containing nitrogen: methanal azine

A harmonic force field was developed for methanal azine. The force constants were used to calculate mean amplitudes of vibration, perpendicular amplitude correction coefficients and Coriolis coupling coefficients.     

A new method to evaluate force constants from experimental spectral data

An iterative procedure is proposed to facilitate the determination of molecular vi-brational force constants from the experimental fundamental frequencies. Proper restrictions are introduced to the force constants based on physical considerations for getting reasonable results. The experimental data of Coriolis coupling coefficients and isotopic frequency shifts are utilized to reduce the uncertainty of the calculated force constants when they are available. A series of various kinds of molecules have been calculated by this method and the results are satisfactory.     

Formulation of the vibrational theory in terms of redundant internal coordinates

Using the generalized inverse of matrices and the method of canonical matrices, this paper develops an unambiguous formulation of the theory of small vibrations of molecules which is valid when redundant internal coordinates are used. Such treatment includes the attainment of unambiguous relationships relating the compliance matrix (the generalized inverse of the canonical force constants matrix) with experimental data (vibrational frequencies, Coriolis coupling constants, centrifugal distortion constants and mean-square amplitudes). Moreover, expressions for the elements of the Jacobian matrices of the above magnitudes with respect to the compliance constants have been also obtained as well as some sum rule relationships.     

The general harmonic force field of formaldehyde

The use of recently available frequency, ¹³C frequency shift, Coriolis coupling, and centrifugal distortion data enables the GHFF of formaldehyde to be determined with some degree of precision. Excellent agreement is obtained between the experimentally determined interaction force constants and those predicted by the most recent ab initio calculations of Meyer and Pulay.     

Molecular vibrational constants of some simple polyatomic molecules: trihalogenomethanes,CHX3 and trihalogenosilanes,SiHX3 (X = F,Cl, Br)

Force constants and compliance constants for the CHX₃ and SiHX₃ molecules have been obtained, using the vibrational frequencies of CHX₃ and CDX₃ (SiHX₃ and SiDX₃) molecules only. The reliability of the resulting force field has been checked by calculation of Coriolis coupling constants, centrifugal distortion constants and mean amplitudes of vibration and by comparison with the available experimental data.     

Isotopic invariants of pyramidal symmetrical XY3 molecules and evaluation of molecular constants

The isotopic invariants of pyramidal symmetrical XY₃ molecules are calculated in terms of frequencies, Coriolis coupling constants, molecular geometry parameters and masses of the constituent atoms. These invariants are used to evaluate force constants, compliance constants and mean amplitudes of vibration of four sets of 12 isotopic molecules.     

Force constants,coriolis coupling constants and mean amplitudes of vibration of GaF63− and FeF63−

The force constants, Coriolis coupling constants and mean amplitudes of vibration at 0, 298.16 and 500 K for GaF₆^3?FeF₆^3? have been reported for the first time employing recent vibrational data. The results are discussed in the light of available information.     

Molecular dynamics of germylacetylene

A complete vibrational analysis has been carried out for germylacetylene and germylacetylene-d₃ molecules and a set of molecular constants, i.e. kinetic constants and potential constants, is reported. The physical understanding of the nature of the potential constants and kinetic constants in molecules leads to a stringent application of provisions of group theoretical technique, introduced by Wilson in the study of molecular vibrations. This procedure is applied here to the evaluation of mean amplitudes of vibration. Coriolis coupling constants and centrifugal distortion constants of these cases, with highly satisfactory results. The values of Coriolis coupling constants and centrifugal distortion constants are in good agreement with the observed values for the germylacetylene molecule showing the significance of the procedure adopted in the present study.     

Molecular potential functions from joint analysis of gas electron diffraction and spectroscopic data

A joint analysis of electron diffraction and spectroscopic data is carried out for BF₃, PBr₃, AsBr₃, SbCl₃, SeO₂ and ClO₂ in terms of the harmonic force fields. The scheme of analysis was extended to include the following spectroscopic observables: vibrational frequencies, rotational, Coriolis coupling and centrifugal distortion constants and, whenever available, those for the isotopic species. For ClO₂ a simplified anharmonic analysis was also performed, the anharmonic spectroscopic observables being involved in this case.

Compelling evidence has been presented that the conventional harmonic approximation for the force field in terms of rectilinear internal coordinates yields the simplest satisfactory representation of diffraction and spectroscopic observations. However, a consistently better fit to experimental data was found when natural curvilinear internal coordinates were used. It is shown here that for the systems considered the joint analysis of data from various sources ensures that reliable and accurate values for equilibrium distances and force field parameters are obtained. The optimized values of spectroscopic constants, structural and force field parameters obtained are presented and compared with those available from the literature.     

Potential constants and Coriolis coupling constants of perhalogenated ethylenes: Part 3. trans-ClFC=CFCl, trans-ClBrC=CBrCl and trans-FBrC=CBrF

Based on vibrational frequencies a calculation of a general quadratic force field has been carried out for trans-ClFC=CFCl, trans-ClBrC=CBrCl and trans-FBrC=CBrF via an iterative method. The resulting transformation L matrices were used to evaluate the Coriolis coupling constants and these were used to calculate inertial defects. The calculated values of the inertial defects are lower than those of the respective cis-ethylene-type molecules.     

Molecular vibrational constants of some simple polyatomic molecules: Difluoro- and dichlorosilane, dichloro- and dibromogermane, and trichlorogermane

Normal coordinate calculations are carried out for difluoro- and dichlorosilane, dichloro- and dibromogermane, and trichlorogermane. Force constants, centrifugal distortion constants, Coriolis coupling constants and mean amplitudes of vibration are reported and discussed in relation to some previously published data.     

A force field study of diacetylene molecule by kinetic constant method

The potential constants of diacetylene molecule has been evaluated using kinetic constants. The other molecular constants such as the generalised vibrational mean amplitudes, shrinkage constants, Coriolis coupling constants and centrifugal distortion constants are also calculated using the vibrational frequencies and the results discussed.     

Potential constants and Coriolis coupling constants of perhalogenated ethylenes Part 1. 1,1-Cl2C=CF2, 1,1-Cl2C=CBr2 and 1,1-F2C=CBr2

Coriolis coupling constants have been calculated from force field computations and used to evaluate the inertial defect of 1,1-dichlorodifluoroethylene, 1,1-dichlorodibromoethylene and 1,1-difluorodibromoethylene. The inertial defect values for the ground vibrational state of 1,1-C1₂C=CF₂ = 0.2450, 1,1-Cl₂C=CBr₂ = 0.3740 and 1,1-F₂C=CBr₂ = 0.4190 amu Ų show corrrespondence with the observed values of similar ethylene-type molecules.     

Potential constants and Coriolis coupling constants of perhalogenated ethylenes: Part 2. cis-ClFC=CFCl, cis-ClBrC=CBrCl and cis-FBrC=CBrF

Potential energy constants and Coriolis coupling constants, calculated for cis-dichlorodifluoroethylene, cis-dichloro-dibromoethylene and cis-difluorodibromoethylene, reproduced the vibrational frequencies and fulfilled the sum rules respectively. Inertial defect calculated values for the ground vibrational state of these molecules show good correspondence with the reported values for similar ethylene-type molecules.     

Molecular constants of substituted ethylene-type molecules: IV. Inertia defects and rotational constants of vinyl halides and their deuterated derivatives

The inertia defects of some vinyl halides and their deuterated derivatives have been calculated on the basis of the general formulation developed by Oka and Morino. The initial sets of Urey-Bradley force constants, based on published data, were adjusted by a least squares procedure until they reproduced the fundamental vibrational frequencies satisfactorily. The Coriolis coupling constants which satisfy the sum rules derived were evaluated and used to calculate the inertia defect in the ground vibrational state. The theoretical values of the inertia defect are used to determine the rotational constant A which cannot otherwise be accurately determined from an “a” type transition.     

Matrix isolation infrared study and molecular force field of HSiCl3

The infrared spectrum of HSiCl₃ in argon, krypton and nitrogen matrices has been studied to measure the chlorine and silicon isotope frequency shifts. Force constants have been determined from the vibrational frequencies, isotope shifts, Coriolis coupling constants and centrifugal distortion constants.     

Anharmonic analysis of the vibrational spectra of some cyanides and related molecules of astrophysical importance

A detailed analysis of the vibrational spectra of carbonyl cyanide, diethynyl ketone and acetyl cyanide has been conducted in harmonic and anharmonic approximations. RHF, MP2 and density functional theory (DFT) methods with 6-311++G(2df,2p) basis sets and B3LYP functionals have been employed. Spectroscopic constants such as anharmonicity constants, rotational and centrifugal distortion constants, rotation-vibration coupling constants and Coriolis coupling coefficients have been calculated for each molecule and compared with the experimental data, where available. A close agreement between the calculated and experimental values of the spectroscopic constants has been obtained. Complete assignments have been provided to the fundamental bands, overtones and combination tones of the molecules. Density functional theory based anharmonic frequencies compare well with the experimental frequencies within +/-18 cm(-1) on an average. RHF and MP2 methods, however, give much higher values for the frequencies that need scaling even in the anharmonic approximation.     

Anharmonic analysis of the vibrational spectrum of ketene by density functional theory using second-order perturbative approach

The paper reports main results of a comprehensive study of the vibrational spectrum of ketene computed using second-order perturbation theory treatment based on quartic, cubic and semidiagonal quartic force constants. Two different models--a homogeneous model using the same density functionals and basis functions for the harmonic calculations and anharmonic corrections, and a hybrid model in which the two parts of the calculation are conducted using different density functionals and basis sets--have been employed in the present calculations. Different DFT and CCSD methods and DZ and TZ extended basis sets involving diffuse and polarization functions have been used to calculate optimized and vibrationally averaged geometrical parameters, the harmonic and anharmonic vibrational frequencies and the spectroscopic constants such as anharmonicity constants, rotational constants, rotation-vibration coupling constants, Nielsen's centrifugal distortion constants and Coriolis coupling constants. Homogeneous model is found to be superior to the hybrid model in several respects. Difficulties in the hybrid model may arise due to one of the following reasons: (a) the basic requirement that the geometry optimization and frequency calculations must be done at the same level of theory to have valid frequencies is not met in the hybrid model; (b) the molecular structure gets reoptimized at the low level for anharmonic corrections; (c) in addition, the perturbation could also diverge for the above reasons, particularly for the very low, very anharmonic terms where the harmonic approximation is not close enough to make the perturbation work.     

An overlay calculation of the molecular force field of 2- and 3-halogeno derivatives of thiophene

A normal mode calculation, which includes force constants, vibration mean amplitudes, Coriolis parameters and thermodynamic properties, has been performed on a series of six halogenated thiophenes. The zeroth-order force field we have used is that of the thiophene parent molecule, and some specific force constants and interaction constants have been refined using the overlay technique. Results show that the halogen substitution acts upon the heterocyclic ring motion frequencies as an isotopic substitution, viz. with small electronic effects but with remarkable mass effects.