Stimulated Emission Pumping Spectra and Intramolecular Vibrational Dynamics of DFCO(S0) from 9000 to 20 000 cm-1

Autor: Richard G. Shu, Hakhyun Nam, Harry P. Beal, Horst Clauberg, Jason C. Crane, Ilia J. Kalinovski, C. Bradley Moore
Rok vydání: 1998
Předmět:
Zdroj: The Journal of Physical Chemistry A. 102:9433-9444
ISSN: 1520-5215
1089-5639
DOI: 10.1021/jp981917b
Popis: Dispersed fluorescence (DF) and stimulated emission pumping (SEP) spectra of DFCO from 9000 to 20 000 cm -1 on S0 are reported. Groups of features in the 2 1 5 1 6 2 DF spectrum are assigned as strongly coupled members of 266 [O2(CO stretch) T 2O6(out-of-plane bend)] polyads of vibrational states. The FranckCondon active states in these polyads are primarily the zero-order states 2 n6m with values of n ranging from 0 to 4 and values of m ranging from 13 to 19. The assignment of the Franck-Condon active states is consistent with the HFCO experimental results and with Franck-Condon factor calculations. Multiple intramolecular vibrational energy redistribution (IVR) time scales are evident from the dilution of the Franck -Condon factors observed in the spectra examined at different resolutions. The fastest IVR results from the low-order ( ¢ V) 3) 266 resonance that couples O2 and O6. This initial IVR occurs in 25 fs. Evidence of anharmonic coupling within the vicinity of single DF features signifies subsequent IVR on the 0.5-4.0 ps time scale. This second time scale can be understood in terms of further coupling to O3 (HCO bend) and O5 (FCO bend) resulting from a 3566 Darling-Dennison resonance. Clumps of vibrational lines within individual SEP bands indicate further anharmonic and weak A-type Coriolis coupling to background levels at times between 3 and 150 ps. Comparison of the observed and calculated vibrational-state densities indicates that, for many states, IVR may be nearly complete on the time scale of the measured dissociation rates. The IVR dynamics of DFCO are in marked contrast to the mode-specific IVR dynamics of HFCO. The quasistability of extreme-motion out-of-plane vibrations (V6 g 14), in HFCO is destroyed by the strong coupling of O2 and 2O6 in DFCO. Thus, the two isotopomers display qualitatively different IVR dynamics.
Databáze: OpenAIRE
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