PICOSECOND INVESTIGATION OF THE COLLISIONAL DEACTIVATION OF OH A (2)SIGMA(-PRESSURE FLAME()(V' = 1, N' = 4, 12) IN AN ATMOSPHERIC)

The collisional deactivation of the laser excited states A (2) Sigma() (upsilon' = 1, N' = 4, 12) of OH in a flame is studied by measuremen t of spectrally resolved fluorescence decays in the picosecond time do main. Quenching and depolarization rates, as well as vibrational energ y-transfer (VET) and rotational energy-transfer (RET) rates are determ ined. An empirical model describes the temporal evolution of the quenc hing and VET rates that emerge from the rotational-state relaxation. F itting this model to the measured 1-0 and 0-0 fluorescence decays yiel ds the quenching and VET rates of the initially excited rotational sta te along with those that correspond to a ratationally equilibrated vib ronic-state population. VET from the higher rotational state (N' = 12) shows a tendency for resonant transitions to energetic close-lying le vels, RET is investigated by analysis of the temporal evolution of the 1-1 emission band. The observed RET is well described by the energy-c orrected sudden-approximation theory in conjunction with a power-gap l aw. (C) 1998 Optical Society of America.