Rotational state specific dissociation dynamics of D2O via the C̃(010) state: The effect of bending vibrational excitation.

The rotational state resolved photodissociation dynamics of D₂O via the C ̃ (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 C ̃ (010) ← X ̃ (000) band and the corresponding time-of-flight (TOF) spectra of D-atom photoproducts formed following the excitation of D₂O to individual rotational transition have been measured. By comparison with the action spectrum of the C ̃ (000) ← X ̃ (000) band, the bending vibrational constant of the C ̃ state for D₂O can be determined to be v₂ = 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 C ̃ (010) state to the low-lying electronic states: the homogeneous electronic coupling to the ùB₁ state, resulting in vibrationally hot OD(X) products, and the Coriolis-type coupling to the B ̃ ¹A₁ 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 C ̃ → ¹A₂ or C ̃ → à pathway. In comparison with the previous results of D₂O photolysis via the C ̃ (000) state, it is found that the v₂ vibration of the parent molecule enhances both the vibrational and rotational excitations of OD products. [ABSTRACT FROM AUTHOR]