ROTATION-VIBRATION STATE-RESOLVED UNIMOLECULAR DYNAMICS OF HIGHLY EXCITED CH3O((X)OVER-TILDE(2)E) .2. INTRAMOLECULAR VIBRATIONAL DYNAMICS OF EXCITED C-O STRETCH STATES

The stimulated emission pumping (SEP) spectra of highly excited CH3O ( X (2)E) reported in the preceding paper [A. Geers, J. Kappert, F Temps , and J. Wiebrecht, J. Chem. Phys. 101, 3618 (1994); paper I] are anal yzed to extract quantitative data on the collision-free intramolecular vibrational dynamics of the molecules. Attention is focused on the sp ectra and dynamics of the excited C-O stretch vibration (nu 3) states at energies between 3 000 cm(-1)less than or equal to E less than or e qual to 10 000 cm(-1). The spectra are found to exhibit a rather sudde n transition at E approximate to 5000 cm(-1) from the regular, assigna ble properties at low energies to the ''statistical'' region at high e nergies. This IVR ''threshold'' is approximately 2000 cm(-1) below the asymptotic H-H2CO dissociation limit of the molecule. The observed de nsities of states at these energies approach the full J- and symmetry- sorted rovibronic densities estimated from harmonic state counts. The nearest-neighbor level spacing distribution in the spectra and the mag nitude of the inferred root mean square level coupling matrix elements support the assumption of nearly ''ergodic'' molecular properties in this region. From computed time autocorrelation functions, the IVR lif etimes of the highly excited C-O stretch states are found to be of the order of tau approximate to 0.2-0.3 ps (nu(3)=5 to 6) Evidence is obt ained from some spectra for two-tier IVR processes with characteristic time scales of 0.2 and 2 ps, respectively. The highest excited C-O st retch states at energies above approximate to 8000 cm(-1) (nu(3) great er than or equal to 8) appear to be coupled only weakly to neighboring background states. This last observation hints at the existence of qu asistable periodic orbits, which are embedded in the quasicontinuum of dissociative states at these energies.