PHOTOLYSIS OF METHANE AT 1236-A - QUANTUM YIELD OF HYDROGEN FORMATION

Pure CH4 and CD4 have been separately but simultaneously photolyzed at 1236 A by means of a split-cell technique in order to obtain accurate relative quantum yields for the various modes of production of H2 and D2. The split-cell technique has been used to obtain quantum yields by comparison with the CO2 actinometer. Molecular elimination yields for CD4 and CH4 (0.58) are found to be equal, while the H-atom yield greatly exceeds the D-atom yield. It is concluded from the results that a significant fraction of the atoms produced disappears by the association reaction M+H+CH3→ CH 4+M. The effect of scavengers and inert gas also have been investigated. The total quantum yield for H and H2 formation is greater than unity and fragmentation of CH2 or CH3 formed in the primary process is suggested: CH3 → H+CH2 CH2 → H+CH However, the lower limit for the quantum yield for D and Da formation is 0.76 and indicates that fragmentation of CD2 or CD3 is less important than that of the corresponding protonated species.