Collision-induced predissociation in the gas phase. Photolysis of methanol at 1849 Å

Abstract

The methanol photodecomposition quantum yield increases with the addition of different foreign gases (alkanes, rare gases, CO₂, SF₆). Whereas the methanol absorption spectrum presents a continuum in the 1850 Å region, the added gas effect implies that collisions are involved in reaching the dissociative state. This apparent contradiction between photochemical and spectroscopic data leads to the postulate of the existence of a collision-induced predissociation. The efficiency of the different gases in promoting the predissociation correlates with their polarizability. In absence of spin-orbit coupling, the collision-induced predissociationc an be explained on the basis of a van der Waals interaction. With Kr and Xe as added gases, spin-orbit coupling is an additional dissociative channel.