Photodissociation Dynamics of the [O2-H2O]+ Ionic Complex

We present an experimental study on the photodissociation dynamics of [O-2-H2O](+) in the 580-266 nm wavelength range using a cryogenic ion trap velocity map imaging spectrometer. The cryogenic ion trap produces mass selected and internally cold [O-2-H2O](+) ions for photodissociation. By detecting both the O-2(+) and H2O+ photofragments using the time-of-flight mass spectrometry and velocity map imaging techniques, branching ratios and total kinetic energy release distributions of the O-2(+) + H2O and H2O+ + O-2 product channels are experimentally measured at 16 different excitation energies. State-resolved photodissociation mechanisms of the parent [O-2-H2O](+) are interpreted as (1) the O-2(X-3 Sigma(-)(g)) + H2O+ (X similar to B-2(1)), O-2(a(1)Delta(g)) + H2O+ (X similar to B-2(1)), and O-2(X-3 Sigma(-)(g)) + H2O+ (A similar to(2)A(1)) channels are produced from direct dissociation of [O-2-H2O](+) in its excited B similar to(2)A'', D similar to(2)A'', and F similar to(2)A' states, respectively; (2) the O-2(+)(X-2?(g)) + H2O (X similar to B-1(1)) channel is produced from nonadiabatic relaxations of the excited B similar to(2)A'', D similar to(2)A'', and F similar to(2)A'' states to the X similar to(2)A'' ground state with subsequent dissociation. The latter nonadiabatic processes involve charge-transfer on the potential energy surfaces, and the charge-transfer probabilities are determined from experimental results. The dissociation energy of the ground state to the lowest dissociation limit is experimentally refined as D-0 = 1.05 +/- 0.05 eV. This work provides important information to understand the charge-transfer dynamics in the photochemistry of [O-2-H2O](+) and in the ion-molecule reaction O-2 + H2O+ -> O-2(+) + H2O.