Molecular emission from H₂O/D₂O<i>[Ctilde]</i>¹<i>B</i>₁and photodissociation dynamics on the<i>[Btilde]</i>¹<i>A</i>₁surface

Abstract

Abstract Bound to free emission centred near 420nm is reported from heavily predissociated levels of H2O/D2O [Ctilde](1 B 1)000 (τ < 6ps) to the dissociative à 1 B 1 state. The quantum yield for fluorescence is small (∼ 10-4) and provides an estimate for the radiative lifetime of the D2O ([Ctilde] → Ã) emission. The ([Ctilde] → Ã) fluorescence excitation spectrum has been modelled to obtain refined heterogenous predissociation rates for D2O ([Ctilde] 1 B 1 → [Btilde] 1 A 1) transfer. This has allowed the OD(A 2Σ+) photofragment fluorescence excitation spectrum to be modelled to obtain the J′a dependent Renner-Teller crossing probability for [Btilde] 1 A 1 → à 1 B 1 transfer during dissociation, over a wide range of a-axis rotation. The results are in good, qualitative agreement with theory and provide insight into the dynamics of dissociation on the [Btilde] 1 A 1 surface. Resolved photofragment fluorescence excitation spectra for selected rotational levels N′, in OD (A 2Σ+)v′ = 0 show a correlation between N′ and the [Btilde] → à crossing probabilities. This provides experimental evidence for the correlation between ‘direct’ trajectories and high product rotation and between ‘indirect’, bending trajectories and low product rotation, as suggested by previous 3-D scattering calculations. The effect of this correlation and of the intersections of [Btilde] 1 A 1 with à 1 B 1 and [Xtilde] 1 A 1, on the [Btilde] state dynamics and on the OD (A 2Σ+) quantum yield, rotational distributions and alignments are discussed.