Coriolis coupling constants of cis and trans-1,2-dichloroethylene

Coriolis coupling constants and the inertia defect for cis- and trans-1,2-dichloroethylene have been calculated, using force constants obtained by the iterative consistency method. The results obtained are compared with those of previous workers and it is shown that two sets of force constants which reproduce the vibrational frequencies satisfactorily lead to completely different values for the Coriolis coupling constants.     

Constrained force constants for octahedral molecules

A set of constrained force constants has been derived from experimental vibrational frequency data for eighty three octahedral molecules. Superimposing the condition that the larger value for f_d—f_dd′ be used when f_dα—f_dα″ is a maximum on the six equations relating vibrational frequencies to force constants generates a seventh. This provides a uniform set of results for all 83 molecules. The values of the force constants have a simple rationale in terms of chemical bonding theory. Some preliminary calculations for SF₆ show that these force constants are suitable for use in generating reliable molecular dynamical trajectory data.     

Vibrational modes and force constants ofp-bromotoluene

The characteristic features of the normal vibrational modes ofp-bromotoluene were calculated; the assignments of spectral bands reported previously were corrected. The force constants of the molecule were estimated in terms of the model of the unified valence and force field.     

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.     

Planarity of 1-chloroborepin

The microwave spectrum of (³⁵Cl,¹¹B)-1-chloroborepin was obtained and the rotational constants in the ground state derived. The principal moments of inertia obtained from the rotational constants were used to calculate the inertia defect Δ=−0.19 uŲ. From this evidence, we conclude that 1-chloroborepin is a planar molecule.     

Millimeter-wave rotational transitions and molecular constants of the diatomic silver iodide

In the 280 GHz region four rotational transitions of both isotopic species of AgI in vibrational states up to v = 2 have been measured. The analysis including frequencies of former observations in the 10 GHz region resulted in improved and new Dunham parameters Y_kl. From these data values of the vibrational constants ω_e and ω_ex_e have been deduced.     

Prediction of vibrational constants for gas-phase heteronuclear diatomics and atoms adsorbed on surfaces

An empirical relationship is presented for predicting vibrational constants for gas-phase heteronuclear diatomic molecules and atoms adsorbed on surfaces. Excellent agreement with experimental values is obtained. The method is used for predicting the unknown vibrational constants of AgS and CTe.     

Zero-point vibrational corrections to isotropic hyperfine coupling constants in polyatomic molecules

The present work addresses isotropic hyperfine coupling constants in polyatomic systems with a particular emphasis on a largely neglected, but a posteriori significant, effect, namely zero-point vibrational corrections. Using the density functional restricted-unrestricted approach, the zero-point vibrational corrections are evaluated for the allyl radical and four of its derivatives. In addition for establishing the numerical size of the zero-point vibrational corrections to the isotropic hyperfine coupling constants, we present simple guidelines useful for identifying hydrogens for which such corrections are significant. Based on our findings, we critically re-examine the computational procedures used for the determination of hyperfine coupling constants in general as well as the practice of using experimental hyperfine coupling constants as reference data when benchmarking and optimizing exchange-correlation functionals and basis sets for such calculations.     

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.     

Inertia defects of urea

By means of an iterative consistency method it has been determined a complete potential field for the urea molecule. The force constants set which interpretates well the vibrational spectra of urea and its deutero derivatives has been used to evaluate rovibrational constants. The calculated inertia defects should confirm a non-planar structure for urea in gaseous phase.     

Ab initio study of force constants and intensities of 1,3,5-trioxane

The structure, vibrational force constants and infrared and Raman intensities have been calculated for 1,3,5-trioxane using a 3-21G basis set. These results have been used to identify some possible inaccuracies in experimental diffraction based structures and in vibrational assignments. It is demonstrated that there is a marked contrast between the trends in the vibrational force constants and in the King's effective atomic charges of the axial and equatorial CH bonds in the series cyclohexane, 1,4-dioxane and 1,3,5-trioxane. The axial CH stretching force constant decreases by 0.04 mdyne Å⁻¹ for each adjacent oxygen atom, whereas that of the equatorial CH bond increases by 0.15 mdyne Å⁻¹ per oxygen. In trioxane the effective atomic charge of the axial hydrogen is twice that of the equatorial. Atomic polar tensors are calculated in a bond oriented frame, and the effect of the oxygens on CH stretching and bending mode intensities discussed. Some properties are also calculated using the 4-31G basis.     

Microwave spectrum,rotational constants and dipole moment of s-cis acrolein

The microwave spectrum of a second conformer of acrolein is reported for the first time. Ground-state rotational constants and quartic centrifugal distortion constants were determined from 42 transitions in the range 8–60 CHz. The small inertial defect establishes its planarity. The dipole moment of s-cis acrolein is μ_a = 2.010(5) D, μ_b = 1.573(3) D and μ_total = 2.552(3) D.     

Ab initio rovibrational states and infrared spectrum of RbCN

Using an ab initio potential surface the rovibrational states of RbCN are calculated in the atom-(rigid) diatom formalism. From these, infrared transition intensities and vibrationally averaged dipole moments are obtained, using an ab initio dipole surface. The lower vibrational states can be labeled by bend and stretch, for which the fundamental frequencies are 100.4 and 258.0 cm⁻¹. At energies higher than 500 cm⁻¹, many overlapping resonances are found and the vibrational labeling breaks down. The calculated ground-state rotational constants are A = 2.269 cm⁻¹, B = 0.106 cm⁻¹ and C = 0.100 cm⁻¹, with an inertial defect ΔI = 0.687 amu Ų. For the higher vibrational states these parameters are used to study the increasing floppyness of the molecule and its behaviour as an effective linear isocyanide in excited states. At low temperature, the vibrational absorption spectrum only contains the fundamental transitions plus a transition caused by a Fermi resonance between the stretch fundamental and the third bending overtone. At high temperature, the chaotic and quasi-linear states have a marked effect on the absorption spectrum.     

Hyperfine structure,mm wave rotational spectrum and molecular constants of the diatomic IF in its electronic ground stateX 1 Σ+

At wavelengths near 1 mm the rotational transitionsJ=16←15 and 17←16 of the diatomic IF have been observed. The strong hyperfine transitions ΔF=+1 were measured in vibrational statesv=0, 1 and 2. The much weaker ΔF=0 components could be detected in the rotational transitionJ=17←16 of the molecule in its ground vibrational state. The analysis including previous measurements at larger wavelengths resulted in improved hyperfine parameters, an extended set of Dunham energy coefficients and potential constants.     

Semiclassical calculation of energy transfer in polyatomic molecules. XI. Cross sections and rate constants for Ar + CO2

Data from electron gas calculation on the short-range potential and theoretical van der Waals coefficients C_n (n = 6, 8) have been used to construct a potential surface for the Ar+CO₂ system. The surface has been used to calculate: second virial coefficient, viscosity and diffusion coefficient, rotational relaxation rates, rate constants for vibrational transitions in CO₂ and high-enery/small-angle differential cross sections.     

The computed force constants and vibrational spectra of toluene

The complete harmonic force field and dipole moment derivatives have been computed for toluene at the Hartree-Fock level using a 4-21G basis set. The six scale factors optimized for benzene were used to scale the computed harmonic force constants of toluene. The vibrational frequencies of toluene computed from this scaled quantum mechanical force field are quite good. After a correction was made to two previously proposed spectral assignments, the mean deviation from the experimental frequencies is only 7.8 cm^?1 except for the frequencies related to the methyl group. Five more scale factors for the vibrational modes of the methyl group were reoptimized. The final comparison showed an overall mean deviation of 7.5 cm^?1 between the theoretical spectrum and the experimental spectrum. Computed intensities are qualitatively in agreement with experiments. They are highly useful in the investigation of questionable assignments.     

Calculation of force constants and vibrational frequencies of octahedral MX6 molecules

The vibrational frequencies of some octahedral species ([SbX₆]⁻, [SbX₆]³⁻, [NbX₆]⁻, [NbX₆]²⁻, [TaX₆]⁻, [TaX₆]²⁻; X = F, Cl, Br, I) have been calculated by means of six extrapolated molecular force constants using some linear relations between the force constants and the reciprocal radii of the ligands. A statistical treatment of these correlations allowed the calculation of error limits for a probability of 90%. The computations of the force constants and vibrational frequencies were based on the GF-matrix method.     

Theoretical study of anharmonic force field and spectroscopic constants for 1-chlorophosphaethene,CH2PCl and CD2PCl

The anharmonic force field and spectroscopy constants for CH₂PCl are determined using CCSD(T), VPT2, and density functional theory employing cc-pVQZ basis sets. The molecule structure, rotational spectroscopic constants, and vibrational wave numbers are compared with the available experimental data. Anharmonicity constants, vibration-rotation interaction constants and cubic force constants are predicted. Vibrational wave numbers and rotational constants for CD₂PCl are also determined using the same levels. The isotopic shifts of vibrational wave numbers are remarkable by D atom substitution for 1-chlorophosphaethene.