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PUBLICATIONS

Beyond the Born-Oppenheimer Approximation: High-Resolution Overtone Spectroscopy of H2D+ and D2H+

Published

Author(s)

M Farnik, S Davis, David Nesbitt

Abstract

Transitions to overtone 2upsilion}2 and 2upsilion}3 and combination upsilion}2+upsilion}3 vibrations in jet-cooled H2D+ and D2H+ molecular ions have been measured for the first time by high-resolution IR spectroscopy. The source of these ions is a pulsed slit jet supersonic discharge, which allows for efficient generation, rotational cooling, and high frequency (100 KHz) concentration modulation for detection via sensitive lock-in detection methods. Isotopic substitution and high-resolution overtone spectroscopy in this fundamental molecular ion permit a systematic, first principles investigation of Born-Oppenheimer breakdown effects due to large amplitude vibrational motion, as well as provide rigorous tests of approximate theoretical methods beyond the Born-Oppenheimer level. The observed overtone transitions are in remarkably good agreement(<0.2 cm-1) with theoretical predictions of Tennyson and co-workers (J. Tennyson, private communication), with small but systematic deviations for 2upsilion}2, upsilion}2 + upsilion}3, and 2upsilion}3 excited states indicating directions for further improvement in such non-Bom-Oppenheinier treatments. Spectroscopic assignment and analysis of the isotopomeric transitions reveals strong Coriolis mixing between near resonant 2upsilion}3 and upsilion}2 + upsilion}2 + upsilion}3 vibrations in D2H+. Population-independent line intensity ratios for transitions from common lower states indicate excellent overall agreement with theoretical predictions for D2H+, but with statistically significant discrepancies noted for H2D+, but with statistically significant discrepancies noted for H2D+. Finnally H2D+ vs. D2H+ isotopomer populations are analyzedas a function of D2/H2 mixing ratio and can be well described by steady state kinetics in the slit discharge expansion.
Citation
Journal of Chemical Physics
Volume
116
Issue
No. 14
Pub Type
Journals

Keywords

high-resolution spectra, isotopomeric transitions, spectroscopy, steady-steady kinetics

Citation

Farnik, M. , Davis, S. and Nesbitt, D. (2002), Beyond the Born-Oppenheimer Approximation: High-Resolution Overtone Spectroscopy of H<sub>2</sub>D<sup>+</sup> and D<sub>2</sub>H<sup>+</sup>, Journal of Chemical Physics (Accessed October 26, 2025)

Issues

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Created December 31, 2001, Updated October 12, 2021
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