Rotational state specific dissociation dynamics of D 2 O via the C̃(010) state: The effect of bending vibrational excitation.

The rotational state resolved photodissociation dynamics of D ₂ O via the C̃(010) state has been investigated by using the D-atom Rydberg tagging time-of-flight technique combined with a tunable vacuum ultraviolet light source. The D-atom action spectrum of the C̃(010) ← X̃(000) band and the corresponding time-of-flight (TOF) spectra of D-atom photoproducts formed following the excitation of D ₂ O to individual rotational transition have been measured. By comparison with the action spectrum of the C̃(000) ← X̃(000) band, the bending vibrational constant of the C̃ state for D ₂ O can be determined to be v ₂ = 1041.37 ± 0.71 cm ^-1 . From the TOF spectra, the product kinetic energy spectra, the vibrational state distributions of OD products, and the state resolved anisotropy parameters have been determined. The experimental results indicate a dramatic variation in the OD product state distributions for different rotational excitations. This illuminates that there are two distinctive coupling channels from the C̃(010) state to the low-lying electronic states: the homogeneous electronic coupling to the à ¹ B ₁ state, resulting in vibrationally hot OD(X) products, and the Coriolis-type coupling to the B̃ ¹ A ₁ state, producing vibrationally cold but rotationally hot OD(X) and OD(A) products. Furthermore, the three-body dissociation channel is confirmed, which is attributed to the C̃ → ¹ A ₂ or C̃ → à pathway. In comparison with the previous results of D ₂ O photolysis via the C̃(000) state, it is found that the v ₂ vibration of the parent molecule enhances both the vibrational and rotational excitations of OD products.