Vibration Rotation Coupling Constants Research Articles

Equilibrium geometry of HC3N

A near-equilibrium potential energy surface has been calculated for cyanoacetylene, HC3N, by means of the coupled electron pair approximation (CEPA) using a basis set of 118 contracted Gaussian-type orbitals, and from it vibration-rotation coupling constants αv and 1-type doubling constants qt and qJ t have been calculated for various isotopomers by standard perturbation theory. By the combination of experimental B 0 and theoretical αv values for six different isotopomers we were able to determine an accurate equilibrium geometry: r e(HC(1)) = 1·0624 A, R 1e(C(1)C(2)) = 1·2058 A, R2e(C(2)C(3)) = 1·3764 A and R 3e(C(3)N) = 1·1605 A. A conservative estimate of the error in the equilibrium bond lengths is 0·0005 A.

A theoretical investigation of HC 2NC and HNC 3

A near-equilibrium potential energy hypersurface has been calculated by CEPA-1 for HC 2NC, a molecule of astrochemical interest. Making use of experimental ground-state rotational constants and ab initio values for the vibration—rotation coupling constants, the equilibrium bond lengths have been determined with 0.0005 Å accuracy. Various spectroscopic properties have been calculated and are compared with recent experimental data. The less stable HNC 3 is obtained to be quasi-linear; the calculated data are in support of Kawaguchi's assignment of three interstellar lines to this species.

C 3O: ab initio calculations and matrix IR spectra

The equilibrium geometry of linear C 3O has been calculated with high precision (≈ 0.0005 Å accuracy) by combining experimental ground-state rotational constants and theoretical vibration-rotation coupling constants. The results are R 1e (C 1C 2)=1.2717 Å, R 2e(C 2C 3)=1.2965 Å and R 3e(C 3O)=1.1473 Å. New matrix IR spectra show a larger number of peaks not observed before which are assigned to overtones and combination tones. In addition, the very weak ν 3 fundamental was found at 939.1 cm −1. Its intensity is much smaller than that of the corresponding first overtone as theoretically predicted earlier by one of us.

Ab initio vibration—rotation coupling constants and the equilibrium geometries of NCCN and CNCN

The equilibrium geometries of NCCN and CNCN were calculated from experimental ground-state rotational constants and ab initio values for the vibration—rotation coupling constants. For NCCN, R 1e(NC) = 1.1578(5) Å and R 2e(CC) = 1.3839(5) Å were obtained, where estimated error bars are given in parentheses. The calculated equilibrium bond lengths of CNCN are R 1e(CN) = 1.1813(5) Å, R 2e(NC) = 1.3116(5) Å and R 3e(CN) = 1.1581(5) Å. Ground-state rotational and centrifugal distortion constants are predicted with high accuracy for various isotopomers of NCCN.

The quartic force field of H2O determined by many-body methods. II. Effects of triple excitations

A b initio coupled cluster and many-body perturbation theory methods that include triple excitation effects are applied to the determination of the quartic force field of the water molecule using an extended Slater-type basis set. Predictions of fundamental, overtone, and combination vibrational frequencies, rotational constants, and vibration–rotation coupling constants are reported for H2O and its isotopomers. The best predicted harmonic frequencies for the stretching modes of H2O are accurate to 3 cm−1, while the bending mode has an error of 28 cm−1. The mean absolute error for all frequencies reached by two quanta is 0.6%, while the anharmonic constants xi j have a mean absolute error of less than 3%. The important role of triple excitation effects in the surface determination is discussed, and is compared with the effects of quadruple excitations.

An a b i n i t i o calculation of spectroscopic properties of the azide anion

Using a basis set of 99 contracted Gaussian type orbitals and Meyer’s coupled electron pair approximation (CEPA), several spectroscopic properties such as vibrational frequencies, rotational, and centrifugal distortion, and vibration–rotation coupling constants were calculated for different isotopomers of the azide anion N−3. The ν3 band (asymmetric stretch) of 14N−3 is predicted to be extremely intense.

Coherent Stokes and anti-Stokes Raman spectra of the ν1 ( A1) and ν2 ( E) bands of SF 6 and UF 6

Coherent Stokes and anti-Stokes Raman scattering are used to study the ν 1 and ν 2 spectral band profiles of UF 6 and SF 6. Most of the observed SF 6 “hot” bands are assigned, leading to evaluations of the anharmonicity constants X ij : X 12 = −(2.80 ± 0.30) cm −1, X 14 = −(1.00 ± 0.15) cm −1, X 15 = −(1.00 ± 0.15) cm −1. For UF 6, a tentative assignment of the “hot” bands is made: X 12 = −(1.80 ± 0.30) cm −1, X 13 = −(1.60 ± 0.30) cm −1, X 14 = −(0.20 ± 0.10) cm −1, X 15 = −(0.25 ± 0.10) cm −1, and X 16 = −(0.10 ± 0.05) cm −1. Parameters such as the vibration-rotation coupling constants are determined. For SF 6: α = (7 ± 2) × 10 −5 cm −1 for the ν 2 band and α = −(1.02 ± 0.01) 10 −4 cm −1 for the ν 1 band. The calculated spectral profiles of the coherent Stokes or anti-Stokes spectra, which are in good agreement with experimental results, give values for the resonant and nonresonant parts of the susceptibility in both molecules. They also show, in some cases, the influence of neighboring combination bands.

Molecular constants of nitrous oxide, 14N 216O

The zero-order frequencies, anharmonic and vibration-rotation coupling constants up to fourth order have been calculated for the molecule of nitrous oxide, 14N 2 16O, from a careful analysis of all available experimental data on the vibration-rotation energy levels of the molecule. It was found inevitable to include the fourth-order constants in the energy expression in order to reproduce the recent accurate measurements to within their experimental uncertainties. A thorough study has been made of the various anharmonic interactions influencing the energy levels. To obtain a stable solution for the molecular constants in a least-squares adjustment to the observed energy levels involved in these interactions, it was found necessary to treat the vibrational ( J = 0) and vibrational-rotational ( J > 0) terms simultaneously; a general procedure effecting this calculation is described in detail. With the inclusion of the Fermi interaction connected with matrix elements of the type 〈v 1v 2lv 3J∥v 1−1v 2+2 lv 3J〉 the observed levels up to 5700 cm −1 could be reproduced with a standard deviation of 0.006 cm −1. On the other hand, to attain a satisfactory fit also for the high levels observed in the photographic infrared region (8700 to 12000 cm −1), additional interactions of the type 〈 v 1 v 2 lv 3 | v 1-2 v 2 l v 3+1〉 had to be taken into account. However, the values obtained for the constants respousible for these interactions are not considered entirely satisfactory due to the somewhat inferior accuracy of the available photographic infrared data.