Photodissociation from an in-plane rotation in water as a direct probe of dynamics

The state-to-state photodissociation at 193 nm of the initially prepared in-plane rotational state, 3₀₃, of the fundamental symmetric stretch of water, H₂O, (1,0,0), is studied. Stimulated Raman excitation and coherent anti-Stokes Raman scattering prepare and detect respectively the single rotational state of H₂O (1,0,0). Laser-induced fluorescence and Doppler polarization spectroscopy determine the rotational distribution and the vector correlations respectively of the OH photofragment resulting from the photodissociation of the specific rovibrational state. The distribution is structured and the Λ-doublet ratio in the two spin-orbit states shows preference of the A″ component. The correlations are close to the maximum attainable values expected for an idealized orientation in which the transition dipole moment of the parent is parallel to the fragment angular momentum and perpendicular to its velocity. This shows that experiments which prepare the parent molecule in a particular state before a second laser dissociates it provide a powerful means for molecular dynamics.