A practical procedure is described to measure photofragment μ-v-j correlations using polarized 1+n′ resonance-enhanced multiphoton ionization with a time-of-flight mass spectrometer detector. Following the theory of Dixon [R. N. Dixon, J. Chem. Phys. 85, 1866 (1986)], the correlations are expressed as the moments of a bipolar harmonic expansion of the correlated angular distribution of photofragment velocity and angular momentum (v and j) about the parent molecule transition dipole, μ. At a fixed detection geometry and on a single rotational transition, polarization control of the dissociating or probing light permits selective determination of targeted moments of the bipolar harmonic expansion. The velocity-dependent spherical tensor moments of the angular momentum distribution depend upon these bipolar moments and are given for a general experimental geometry and for general elliptical polarization of the probing light. Several practical experimental geometries are described that isolate and measure targeted bipolar moments. The bipolar moments that can be measured using elliptical probe polarizations are described. A method for analyzing the symmetries of dissociation dynamics is proposed and used to identify the moments unique to the dynamics of chiral systems.

The trajectory of NO X 2 ⌸ ⍀ϭ1/2,3/2 (vϭ0) produced after excitation of 2-chloro-2-nitrosopropane S 1 Ã 1 AЉ is studied by polarized 1ϩ1Ј resonance-enhanced multiphoton ionization with time-of-flight mass spectrometry detection. The correlations among the NO velocity v, angular momentum j, and the S 1 Ã 1 AЉ←S 0 X 1 AЈ ͓n͑N͒,*͑NvO͔͒ transition dipole of the parent molecule are measured. The dissociation occurs by internal conversion to the ground S 0 state or intersystem crossing to the T 1 ã 3 AЉ state and the observed speed distribution of the NO fragments is bimodal. There is no evidence for -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 ␤ 0 0 ͑22͒. The average value of ␤ 0 0 ͑22͒ is Ϫ0.17͑Ϯ0.02͒ at jϷ11.5-22.5, more than five times larger than predicted by statistical phase space theory for dissociation on the S 0 X 1 AЈ 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 ͑jр6.5͒. The -v correlation described by the ␤ 0 2 ͑20͒ bipolar moment does not change with j and its average value is Ϫ0.04͑Ϯ0.01͒ at jϷ12. 5-19.5. The average value of the ␤ 0 2 ͑02͒ bipolar moment describing -j correlation is 0.04͑Ϯ0.02͒ at jϷ7.5-24.5. These results are consistent with a mechanism involving both impulsive force due to a barrier along the reaction coordinate on the T 1 ã 3 AЉ surface and forces resulting from the C-N-O bending and NO torsion about the C-N bond.

A general numerical method is given to extract angular correlations from photodissociation experiments with ion imaging detection. The angular correlations among the transition dipole moment of the parent molecule, μ, the photoproduct recoil velocity, v, and its angular momentum, j, are parametrized analytically using the semiclassical bipolar moment scheme due to Dixon. The method is a forward-convolution scheme which allows quantitative extraction of all measurable bipolar moments and can be applied in experiments with both linearly and circularly polarized probe light. It avoids the cylindrical symmetry limitations of the inverse Abel transform method, traditionally used for extracting photoproduct recoil anisotropy and speed distribution from imaging data. The method presented here also takes into account the possibility of multiple photodissociation channels. The features of the method are illustrated in a two-color 1+1′ REMPI-ion imaging study of the NO photoproduct trajectories resulting from the 650 nm photodissociation of 2-chloro-2-nitrosopropane (CNP). A comparison between experimental and synthetic images is presented for selected experimental geometries. The experimental images for CNP and the results from their fit confirm earlier TOF studies showing that the recoil speed distribution is bimodal with the low and high speed components having average values of approximately 500 and 910 m/s. These components have been previously assigned to dissociation from the S0 and T1 electronic states of the parent molecule, respectively. The experimental results from the current study also confirm that for the high-speed component the product NO velocity vector, v, is preferentially perpendicular to its angular momentum, j [β00(22)=−0.21], and that there is no significant correlation between v and the transition dipole moment μ of the CNP molecule [β02(20)=−0.02].