STATE-SPECIFIC COLLISIONAL ENERGY-TRANSFER IN ELECTRONICALLY EXCITED SIF RADICALS - DRAMATIC CONTRASTS WITH SICL

The collisional removal of state-selected SiF (C2DELTA, upsilon' = 0 o r 1) has been studied by time- and wavelength-resolved laser-induced f luorescence spectroscopy. A series of non-polar quenchers (Ar, He, H-2 , N2, CO2 and CH4) was examined. Rate constants are generally large fo r the molecular quenchers, but are negligible for the noble gases. A c ollisionless radiative lifetime of 94+/-2 ns (2sigma statistical uncer tainty) is also reported for the SiF C2DELTA state, independent of vib rational level. A fraction of the removed C2DELTA excited valence stat e population, varying from 0 to 20% with quencher, is deposited in the nearby B 2SIGMA+ Rydberg state. The resultant B 2SIGMA+ state vibrati onal populations are largely quencher independent and correlate well w ith the Franck-Condon overlap between the initial and product vibronic states, despite the substantial energy gaps involved. These results c ontrast dramatically with those for the nominally isoelectronic states in SiCl: possible explanations for the distinctions are discussed.