BRIDGING THE GAP BETWEEN VAN DER WAALS AND HYDROGEN BONDING: A NEAR-IR STUDY OF THE INTERMOLECULAR MODES IN HCl DIMER
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Date
1999
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Publisher
Ohio State University
Abstract
The near IR combination band spectra of supersonically cooled $(HCL)_{2}$ in the $2900 cm^{-1}$ to $3070 cm^{-1}$ region have been recorded with a high resolution slit jet spectrometer. Seven vibration-rotation-tunneling (VRT) bands are observed, representing 3 (out of 4 total) intermolecular modes (van der Waals stretch $v_{4}$, geared bend $v_{5}$, and out-of-plane torsion $v_{6}$) built as combination bands on either the $v_{1}$ (free) or $v_{2}$ (bound) HCl stretches. Each of the seven combination bands are observed for both the $H^{35}Cl-H^{35}Cl$ and $H^{35}Cl-H^{37}Cl$ isotopomers. Analysis of the rotationally resolved spectra provide spectroscopic constants, intermolecular frequencies, predissociation rates, and isotopic shifts as a function of both intra- and inter-molecular excitation. The intermolecular frequencies are compared with full 6-D quantum calculations of a trial potential surface and discrepencies are discussed. Additionally, comparisons with similar studies on $(HF)_{2}$ and $(DF)_{2}$ are presented. Both tunneling rates and combination band intensities are compared between the chlorine and fluorine build dimers, illuminating dramatic differences in these seemingly similar hydrogen bonded prototypes.
Description
Author Institution: JILA, National Institute of Standards and Technology and Department of Chemistry and Biochemistry, University of Colorado