Ultrafast predissociation-dynamics of water molecules excited to the electronic (C)over-tilde and (D)over-tilde states

Two-photon excitation with femtosecond laser pulses in the spectral range 240-250 nm was used to prepare vapor phase H2O and D2O in the (C) over tilde B-1(1) and (D) over tilde (1)A(1) states. Both states are predissociated via the (B) over tilde (1)A(1) state, forming excited OH/OD(A(2)Sigma(+)) as well as ground state OH/OD(X(2)Pi). We used ultrashort infrared probe pulses, (1.65-2.42 mum) to control the ratio between these excited and ground state fragments originating z from. the dissociation process. Time resolved detection of the OH/OD(A(2)Sigma(+))-->OH/OD(X(2)Pi) fluorescence allows us to monitor the dynamics of the predissociation. For the heterogeneous predissociation out of the (C) over tilde B-1(1) state life times of (0.5 +/- 0.1) ps and (1.2 +/- 0.1) ps were found for H2O and D2O, respectively. The purely homogeneous character of the predissociation out of the (D) over tilde (1)A(1) state was monitored. (C) 2004 American, Institute of Physics.