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 $C_{\text{2v}}$ fashion so as to produce incipiently CH₂ and H₂, and in a $C_{\text{3v}}$ 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 $T_2$ 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 $T_2$ state is produced in an electronically excited state. It follows that, unless there is a crossover from $T_2$ to $E$ , the red bands of CH₂ should be observable in emission when methane is photolyzed.