SUBMILLIMETER-WAVE SPECTROSCOPY OF THE VAN DER WAALS BENDING BAND OF Ar-HBr

Loading...
Thumbnail Image

Date

1999

Journal Title

Journal ISSN

Volume Title

Publisher

Ohio State University

Research Projects

Organizational Units

Journal Issue

Abstract

The Ar-HBr cluster has a large amplitude intermolecular bending motion. The excited states of the van der Waals vibrations were observed by $infrared^{a}$ and far $infrared^{b}$ laser spectroscopy. The cluster has a nearly ``linear'' structure of Ar-HBr in the ground state ($\Sigma_{0}$ state), while the cluster is estimated to have a nearly ``anti-linear'' structure of Ar-BrH in the first excited state ($\Sigma_{1}$ state) of the intermolecular bending vibration. In the present study, we have observed submillimeter-wave transitions of the $\Sigma_{1}-\Sigma_{0}$ band of Ar-HBr generated in a pulsed supersonic jet expansion. The observed band origins of the $\Sigma_{1} - \Sigma_{0}$ bands of $Ar-H^{79}Br$ and $Ar-H^{81}Br$ are 6 and 27 MHz lower than those reported by combination differences of infrared $data^{a}$. The cQq constants in the $\Sigma_{1}$ states were determined for the first time to be $260.90(12)$ and $217.854(98) MHz$ for $Ar-H^{79}Br$ and $Ar-H^{81}Br$, respectively, which agree well with the estimated values (238 and 199 MHz for $Ar-H^{79}Br$ and $Ar-H^{81}Br$) from a potential $calculation^{c}$. The $cos^{-1} \sqrt{\langle\cos^{2}\theta\rangle}$ value is $144.3^{c}$ in the $\Sigma_{1}$ state, which is different from the value, $42.1^{\circ}$, in the ground state, where the $\theta$ is an angle between a cluster axis and a HBr monomer axis.

Description

$^{a}$ J. Han, A.L. McIntosh, Z. Wang, R.R. Lucchese, and J.W. Bevan, Chem. Phys. Lett. 265, 209 (1997). $^{b}$ D.W. Firth, M.A. Dvorak, S.W. Reeve, R.S. Ford, and K.R. Leopold, Chem. Phys. Lett. 168, 161 (1990). $^{c}$ J.M. Hutson, J. Chem. Phys. 91, 4455 (1989).
Author Institution: Institute for Molecular Science

Keywords

Citation