NO μ-v-j correlations in the photofragmentation of 2-chloro-2-nitrosopropane

Abstract

The trajectory of NO X 2ΠΩ=1/2,3/2(v=0) produced after excitation of 2-chloro-2-nitrosopropane S1 Ã 1A″ is studied by polarized 1+1′ resonance-enhanced multiphoton ionization with time-of-flight mass spectrometry detection. The correlations among the NO velocity v, angular momentum j, and the S1 Ã 1A″←S0 X̃ 1A′ [n(N),π*(N=O)] transition dipole μ of the parent molecule are measured. The dissociation occurs by internal conversion to the ground S0 state or intersystem crossing to the T1 ã 3A″ state and the observed speed distribution of the NO fragments is bimodal. There is no evidence for μ-v-j correlations for the products associated with the slow component of the speed distribution. For the higher speed component, the v-j correlation is a function of the NO rotational state, j, and is described by the bipolar moment β00(22). The average value of β00(22) is −0.17(±0.02) at j≊11.5–22.5, more than five times larger than predicted by statistical phase space theory for dissociation on the S0 X̃ 1A′ surface, indicating a moderate preference for a perpendicular orientation of the NO rotational angular momentum and velocity vectors. The v and j vectors are nearly uncorrelated for low NO rotational states (j≤6.5). The μ-v correlation described by the β20(20) bipolar moment does not change with j and its average value is −0.04(±0.01) at j≊12.5–19.5. The average value of the β20(02) bipolar moment describing μ-j correlation is 0.04(±0.02) at j≊7.5–24.5. These results are consistent with a mechanism involving both impulsive force due to a barrier along the reaction coordinate on the T1 ã 3A″ surface and forces resulting from the C–N–O bending and NO torsion about the C–N bond.