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

Published

June 1, 2003

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 (Ņ₂+Ņ₆) combination excitation out of the lower γ_vt=A<-A⁺) and upper (γ_vt=B,_B⁺) tunneling levels, respectively. A third much weaker band (3035.37 cm^-1) is also observed in close proximity with the Ņ₂ + Ņ₆ (γ_vt=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

Pub Type

Journals

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;₆) Spectroscopy in (HCI)₂, Journal of Chemical Physics (Accessed October 9, 2025)