Collisionless formation and rovibronic relaxation of CH and OH from the ir multiphoton photolysis of CH3OH

Abstract

A CO₂ TEA laser has been used to initiate the collisionless multiphoton dissociation of CH₃OH between 1000 and 10 mtorr. The appearance of OH(X ²Π_i) 50±20 nsec after the laser pulse, independent of initial CH₃OH pressure (50–200 mtorr), suggests the primary dissociative channel CH₃OH+nhν→CH₃ +OH(X ²Π_i); although CH₃ could not be correspondingly confirmed. The appearance of CH(X ²Π_r) 70±20 nsec after the OH(X) appearance, independent of initial CH₃OH pressure (70–400 mtorr), suggests secondary collisionless dissociation. Initial rovibronic distributions of OH(X) and CH(X) were determined, as well as characteristic decay time constants. The observation of the relaxation of OH(X) over a 10 μsec time interval after radical onset, allowed the separate characterization of collisional rotational relaxation and translational diffusion.