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Probing Hydrogen Bond Potential Surfaces for Out-of-Plane Geometries: Near-infared Combination Band Torsional (Ņ6) Spectroscopy in (HCI)2

Published

Author(s)

M Farnik, S Davis, David Nesbitt

Abstract

High resolution near IR spectra of jet cooled (HCL)2 are obtained in the 3000 cm-1 to 2070 cm-1 combination band region corresponding to simultaneous excitation of intermolecular out-of-plane torsion (Ņ6) with intramolecular HCl stretching (Ņ1Ņ2) degrees of freedom. Two (H35Cl)2 bands (plus the isotopically mixed H35Cl/H37Clbands) due to Ņ6torsional excitation are observed. High resolution spectral analysis of ground state combination differences and nuclear spin intensity alternation effects permits unambiguous identification of J labeling and tunneling level symmetry, yielding precise rotational constants and vibrational band origins. Comparison with previous far-IR studies suggests assignment of the 3036.52(5) cm-1 and 3014.86 cm-1 bands to bound HCl stretch + torsion (Ņ26) combination excitation out of the lower γvt=A<-A+) and upper (γvt=B,_B+) tunneling levels, respectively. A third much weaker band (3035.37 cm-1) is also observed in close proximity with the Ņ2 + Ņ6vt=A<-A+) origin, which most likely acquires oscillator strength by state-mixing between the dark perturbing state and the Ņ2+6 upper level. These data provide first opportunity for comparison with exact quantum calculations by Qui and Bacic and co-workers on high level ab initio/semiempirical (HCL)2 potential surfaces, which should facilitate further refinement of intermolecular potentials for out-of-place twisting of the hydrogen bond.
Citation
Journal of Chemical Physics
Volume
118
Issue
No. 22

Keywords

HCl dimer, hydrogen bonds, torsion

Citation

Farnik, M. , Davis, S. and Nesbitt, D. (2003), Probing Hydrogen Bond Potential Surfaces for Out-of-Plane Geometries: Near-infared Combination Band Torsional (&#325;<sub>6</sub>) Spectroscopy in (HCI)<sub>2</sub>, Journal of Chemical Physics (Accessed April 14, 2024)
Created May 31, 2003, Updated October 12, 2021