Journal of Physical Chemistry A, Vol.102, No.47, 9433-9444, 1998
Stimulated emission pumping spectra and intramolecular vibrational dynamics of DFCO(S-0) from 9000 to 20,000 cm(-1)
Dispersed fluorescence (DF) and stimulated emission pumping (SEP) spectra of DFCO from 9000 to 20000 cm(-1) on S-0 are reported. Groups of features in the 2(1)5(1)6(2) DF spectrum are assigned as strongly coupled members of 266 [nu(2)(CO stretch) <-> 2 nu(6)(out-of-plane bend)] polyads of vibrational states. The Franck-Condon active states in these polyads are primarily the zero-order states 2(n)6(m) with values of n ranging from 0 to 4 and values of n2 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 (Delta upsilon = 3) 266 resonance that couples nu(2) and nu(6). This initial IVR occurs in similar to 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 nu(3) (HCO bend) and nu(5) (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 (upsilon(6) greater than or equal to 14), in HFCO is destroyed by the strong coupling of nu(2) and 2 nu(6) in DFCO. Thus, the two isotopomers display qualitatively different IVR dynamics.
Keywords:POTENTIAL-ENERGY SURFACE;UNIMOLECULAR REACTION DYNAMICS;RANDOM-MATRIX TREATMENT;DISSOCIATION THRESHOLD;FORMYLFLUORIDE;S0 FORMALDEHYDE;HFCO;STATE;REDISTRIBUTION;1-BUTYNE