Photodissociation dynamics of water at Lyman alpha (121.6 nm)

Laser induced fluorescence studies of hydrogen atom using four-wave mixing technique are reported for the photodissociation of H2O and D2O at Lyα (121.6 nm). The source of dissociating and probe radiation was one and the same (delay time ⩽ 20 ns). The average translational energy of ejected hydrogen atoms (34.5 Kcal/mol) revealed that H2O + hν → H + OH(X2Π) and H2O + hν → H2 + O(1D) were the main dissociation processes. The absolute quantum yield for H2O and D2O were ΦH(H2O) = 1.39 ± 0.09 and ΦH(D2O) = 1.21 ± 0.20, respectively. The branching ratio of HDO, ΦH(HDO)/ΦD(HDO), was found to be 1.66 ± 0.50, following the procedure developed by Shafer et al. [Shafer et al., J. Chem. Phys. 90 (1999) 6807].