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Calculating Feshbach resonances in HCO using an extension of Q im ‐path theory
Author(s) -
Wang Xiaohong,
Bowman Joel M.
Publication year - 2017
Publication title -
international journal of quantum chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.484
H-Index - 105
eISSN - 1097-461X
pISSN - 0020-7608
DOI - 10.1002/qua.25286
Subject(s) - excited state , dissociation (chemistry) , overtone , saddle point , atomic physics , chemistry , physics , excitation , quantum mechanics , spectral line , geometry , mathematics
We present a theoretical study of Feshbach resonances in HCO, using an extension of a previous projection theory [Y. Wang and J. M. Bowman, J. Chem. Phys. 139, 154303 (2013)] that makes use of projections of the normal modes of HCO onto a one‐dimensional rectilinear path along the imaginary‐frequency normal mode of the dissociation saddle point. HCO dissociation is strongly mode specific, because the CH‐stretch is nearly coincident with this path. The projection theory predicts that HCO dissociates with a subpicosecond lifetime for the CH‐stretch excited to the second overtone (ν 3 = 3 ), in agreement with rigorous calculations done 20 years ago. However, the CO‐stretch and HCO bend have small projections on the path and so no dissociation is predicted from the simple theory, even for highly excited states. By making an extension of the projection theory to describe coupling of these modes to the CH‐stretch, dissociation rates can be obtained for these modes. Semi‐quantitative results are obtained using vibrational self‐consistent field/virtual‐state configuration interaction calculations with the code MULTIMODE. The dissociation lifetimes for many states involving excitation of these modes are compared with previous rigorous calculations and experiment and encouraging agreement is found.