Photodissociation of methane at Lyman alpha (121.6 nm)

Abstract

Laser induced fluorescence studies of hydrogen atom using four wave mixing technique are reported for the photodissociation of CH4 and its isotopomers at Ly alpha(121.6 mu). The source of dissociating and probe radiation is one and the same (delay time <= 20 nsec). The average translational energy of ejected hydrogen atoms (50 Kcal/mol) reveals that CH4 + hv -> CH3 + H(S-2) and CH4 + hv -> CH2(a(1)A(1)) + H-2((1)Sigma(g)) are the main dissociation processes. The absolute quantum yield for CH4 and CD4 are the same, Phi(H)(CH4) = Phi(D)(CD4) = 0.31 +/- 0.05. If one divides the experimental H/D ratios from the isotopomers CH3D, CH2D2, CHD3 by the isotopic HID ratios, a value 2 is obtained in all three cases. Overall, the heavier D atoms are more likely than the H atoms to remain attached to the carbon atom.