Qing-shi Zhu

Vibration—rotation Hamiltonian of tetrahedral molecules in the local-mode model

Abstract The stretching vibration—rotation Hamiltonian of tetrahedral molecules is derived in the local-mode model. The result shows that the effective rotational Hamiltonian of a local-mode state gives rise to symmetric-top rotational energy levels, which are quantitatively in good agreement with experiments.

High-resolution spectroscopic study of the (2000) stretching vibrational band and vibrational dependence of rotational constants of silane

Abstract A high-resolution infrared spectrum of the (2000) stretching vibrational band of silane, SiH4, has been recorded and analyzed. The rotational constants obtained, together with those of the (n000), n=3, 4, 5 bands reported earlier, show a striking effect of local mode vibrations on rotational constants and an evolution of local mode vibrations from the first overtone. The vibrational dependence of the rotational constants is calculated with the customary normal mode model including Darling—Dennison resonances. The calculated and observed constants are in good agreement. The results also show that states with large vibrational quantum number play important roles for the emergence of the local mode vibrations in real molecules.

Rotational analysis of the (2000) and (3000) bands and vibration—rotation interaction in germane local mode states

Abstract A high-resolution infrared spectrum of the (2000) stretching vibrational band of germane, GeH 4 , has been recorded and analyzed. The rotational constants and Coriolis coupling parameters obtained, together with those of the (3000) band reported earlier, show the striking effect of local mode vibration. The vibrational dependence of these constants and parameters are discussed in terms of the local mode model. The calculations are in good agreement with observations.

Local-mode rotational structures in the (3000) and (5000) stretching overtone bands of silane

Abstract The (3000) and (5000) stretching overtone bands of silane, SiH 4 , have been observed near 6362 and 10268 cm −1 by Fourier transfer spectroscopy with a resolution of 0.01 cm −1 . In both spectra the pseudo-symmetric-top rotational structure, similar to that observed in the (3000) band of germane, was clearly demonstrated. This indicated that these states are very near the local-mode limit. Some striking intensity anomalies were also found.

Local mode Coriolis quenching in tetrahedral hydrides

Abstract The Coriolis coupling strength in stretching vibrational states of XH 4 species is investigated as a function of the extent of bond localisation by use of the Darling-Dennison resonance formalism of Mills and Robiette. It is shown that the effective vibrational angular momentum 〈 l 〉 in the most local ( n 000) F 2 states diminishes rapidly to zero as the parameter λ/gc M → 0. Correlation diagrams for the variation of 〈 l 〉 with λ/χ M are given for all F 2 states with n = 2, 3 and 4.

Effective rotational Hamiltonian of the local mode vibrational states

Abstract The effective rotational Hamiltonians of the local mode states are derived for XY 2 , XY 3 and XY 4 molecules by averaging the vibration—rotation Hamiltonians using the corresponding local mode vibrational wavefunctions. The results indicate that in a local mode vibrational state the molecular symmetry is reduced by the coupling of H 22 term. A tetrahedral molecule reduces to a C 3 v symmetric top, a symmetric top becomes an asymmetric top, while the degree of asymmetry increases for an asymmetric top. The vibrational dependences of rotational constants and vibration—rotation coupling parameters predicted by present theory are in good agreement with those obtained experimentally from SiH 4 local mode vibrational bands.

The (3000), (4000) and (5000) stretching overtone bands of silane. II, The rotational analysis in a normal-mode picture

Abstract The rotational analysis of high resolution spectra of the (3000), (4000) and (5000) stretching overtone bands of silane is presented here. The results show that the observed symmetric top rotational structure of these bands can be explained by the close coupling of the nv 1 ( A 1 ) and ( n -1)ν 1 + ν 3 ( F 2 ) vibrational states near the local-mode limit. The corresponding molecular constants are derived by least-squares fitting.

The (3000), (4000) and (5000) stretching overtone bands of silane—I. The effect of local-mode vibration on rotational constants

Abstract The (4000) stretching overtone band of SiH4 has been observed near 8347 cm−1. A symmetric top rotational structure, similar to that observed in the (3000) band of GeH4: Q.-S. Zhu, B. A. Thrush and A. G. Robiette, Chem. Phys. Lett. 150, 181 (1988); Q.-S. Zhu and B. A. Thrush, J. Chem. Phys. 92, 2691 (1990) [1], and the (3000) and (5000) bands of SiH4: Q.-S. Zhu, B.-S. Zhang, Y.-R. Ma and H.-B. Qian, Chem. Phys. Lett. 164, 596 (1989) [2], are clearly demonstrated. Three local-mode bands of SiH4, (3000), (4000) and (5000) are analysed in the symmetric top model. A striking effect of local-mode vibration on rotational constants is observed and accounted for in a classical picture of vibrational localization.

High-resolution spectroscopy of ν3 and ν1 + ν3 bands of SiD4

Abstract The high-resolution Fourier transform infrared spectra of the ν 3 fundamental and ν 1 + ν 3 stretching combination bands of silane-d 4 , SiD 4 , have been recorded and analyzed at a resolution of 0.004 cm −1 . The molecular constants of the ground state, ν 3 and ν 1 + ν 3 states were derived. No evidence of the vibrational localization was found in the ν 1 + ν 3 state, indicating a considerable increase in the inter-bond coupling parameter λ due to the deuterium substitution. The calculation shows that the very small interbond coupling parameter λ of SiH 4 is the result of nearly complete cancellation of kinetic and potential couplings, which is no longer the case after deuterium substitution.

Anharmonicity : a route to vibrational localization

Abstract The quenching effect of anharmonicity on the inter-bond coupling and Coriolis interaction is studied. The local to normal mode correlation diagrams for XY 2 and XY 3 stretching overtones up to υ = 60 and 20, respectively, are calculated in the normal mode model with Darling—Dennison resonances included. The results show that the high-energy stretching vibrations tend to be bond-localized owing to the anharmonic (Darling—Dennison) resonances.