ROTATION-VIBRATION STATE-RESOLVED UNIMOLECULAR DYNAMICS OF HIGHLY VIBRATIONALLY EXCITED CH3O ((X)OVER-TILDE(2)E) .1. OBSERVED STIMULATED-EMISSION PUMPING SPECTRA

Using the technique of stimulated emission pumping (SEP) spectroscopy, highly excited vibration rotation states of the CH3O (X (2)E) molecul e were probed up to energies of E less than or equal to 10 000 cm(-1). The highest excitation energies exceed the asymptotic H-H2CO dissocia tion limit of the molecule [Delta(1)H(0)(0)(H-H2CO)approximate to 6900 cm(-1)]. Work was carried out at different experimental resolutions. First, low resolution survey SEP spectra were found to exhibit persist ent vibrational structure up to energies far above the dissociation li mit. The observed main features were found to be assignable, in a zero -order picture that leaves aside possible mode-to-mode couplings, to t he progression of the excited C-O stretch vibration states (nu(3)). Th e widths of the respective features correspond to localized short-time vibrational motion for times of greater than or equal to 0.3 ps (grea ter than or equal to 10 C-O vibrational periods). Second, in high reso lution scans over the coarse vibrational features, characteristic clum ps of individual vibration-rotation eigenstates were revealed. These c lumps are ascribed to distinctive Franck-Condon active bright zero-ord er levels which are mixed with the large number of Franck-Condon inact ive dark bath states. Under carefully selected conditions, the clumps could be attributed to states with defined and well known values of th e total angular momentum quantum number J, which remains as a good qua ntum number in different coupling cases. These clump spectra will be a nalyzed quantitatively in the following paper with respect to their be aring for the intramolecular vibrational dynamics of highly excited CH 3O (X) as a function of vibrational and rotational excitation. From th e observed spectra, quantitative data can be obtained on the rate and extent of collision-free intramolecular vibrational and rovibrational energy redistribution (IVR and IRVR) processes, which would result aft er coherent ultrashort pulse excitation of the molecules.