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State‐resolved collisional energy transfer of OH, NH and H 2 CO by two‐color resonant four‐wave mixing spectroscopy
Author(s) -
Radi P. P.,
Kouzov A. P.
Publication year - 2002
Publication title -
journal of raman spectroscopy
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.748
H-Index - 110
eISSN - 1097-4555
pISSN - 0377-0486
DOI - 10.1002/jrs.929
Subject(s) - chemistry , polyatomic ion , excited state , ground state , atomic physics , diatomic molecule , spectroscopy , molecule , resonance (particle physics) , rotational energy , relaxation (psychology) , molecular physics , analytical chemistry (journal) , physics , chromatography , psychology , social psychology , organic chemistry , quantum mechanics
Extra resonances observed in two‐color resonant four‐wave mixing (TC‐RFWM) spectra, which originate from collision‐induced energy transfer processes, were investigated experimentally and theoretically. It is shown that the resonances yield information on state‐to‐state rotational energy transfer (RET) occurring in the ground and excited states of OH and NH. The measurements were performed in situ in an equilibrium medium of high temperature and high density. The results shed more light on the propensity rules for the change in the fine‐structure label and rotational quantum number of NH. A comparison with a recent investigation of NH RET on the ground‐state potential yielded good agreement. A theoretical frequency‐domain picture was developed with the help of exact (off‐diagonal) relaxation matrices and general four‐level schemes. The theoretical results were compared with measured relative TC‐RFWM intensities of the OH radical obtained in a flame. Furthermore, the investigation on diatomic radicals was extended to the polyatomic formaldehyde (H 2 CO) molecule. Initial cell experiments were performed at low pressure by using CO 2 as a quencher. The observation of collision‐induced resonances in the ground state of H 2 CO indicate the potential of the method for the investigation of RET processes occurring in polyatomic molecules in equilibrium media. Copyright © 2002 John Wiley & Sons, Ltd.