ROTATION-VIBRATION STATE-RESOLVED UNIMOLECULAR DYNAMICS OF HIGHLY EXCITED CH3O ((X)OVER-TILDE(2)E) .3. STATE-SPECIFIC DISSOCIATION RATES FROM SPECTROSCOPIC LINE-PROFILES AND TIME-RESOLVED MEASUREMENTS

Vibration-rotation quantum-state resolved measurements of the unimolec ular dissociation rates of highly vibrationally excited CH3O ((X) over tilde E-2) have been performed over a wide range of excitation energi es (7000 less than or equal to E/cm(-1) less than or equal to 10000). Single excited CH3O ((X) over tilde) quantum states were prepared usin g the method of stimulated emission pumping (SEP). State-specific deca y constants were determined from direct time-resolved measurements usi ng laser-induced fluorescence detection (LIF) of the excited states an d from SEP line profiles measured at higher resolution. In very narrow energy windows, the measured decay constants were found to vary stati stically by up to two orders of magnitude. These state-specific fluctu ations are in contrast with the traditional picture from unimolecular rate theory (e.g. RRKM theory). The fluctuations were analysed statist ically. The average decay rates were found to increase with increasing molecular excitation energy. This general trend could be nicely descr ibed by an RRKM model on average. Indications for small deviations wer e observed at high energies. Viewed in connection with related data on the kinetics of intramolecular vibrational energy randomization (IVR) processes, these deviations may reflect the inherent limitations of s tatistical theory at high energies where dissociation and IVR compete.