Photodissociation of Methane

Abstract

A valence-bond calculation is carried out on the ground and six excited energy levels of methane. The molecule is deformed in a C2v fashion so as to produce incipiently CH2 and H2, and in a C3v fashion to obtain CH3 and H. Potential surfaces are obtained which permit one with classical mechanics to determine the shape of the molecule during its dissociation. The crude calculation leads to three principal results: (1) the lowest excited state is a forbidden E state; (2) in the next-highest allowed T2 state there is a steeper potential gradient in the CH3 and H direction than in the CH2 and H2 direction; the reverse is true for the E state; and (3) the CH2 derived from the allowed T2 state is produced in an electronically excited state. It follows that, unless there is a crossover from T2 to E, the red bands of CH2 should be observable in emission when methane is photolyzed.