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

Abstract

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.

Scalar and angular correlations in CF3NO photodissociation: statistical and nonstatistical channels

“…16 Signal-averaged NO ϩ time-of-flight transients were obtained by adding individual transients for 30000 laser shots in each polarization geometry. A TOF transient measured at polarization geometry case n is converted into a velocity projection distribution function D n (v Z Љ , j) as described in Refs.…”

“…The 585 nm bimodal speed distributions are similar to those observed in the photodissociation of chloronitrosoalkanes. 16,17,21 In the chloronitrosoalkanes, the lower-and higher-speed components of the bimodal distribution have been assigned to dissociation of the energized parent molecule on its S 0 and T 1 surfaces, respectively. The chloronitrosoalkanes are different from CF 3 NO in that they show bimodal speed distributions at all dissociation wavelengths for which the NO product could be observed on the 10 ns timescale of the experiment.…”

“…Experimental studies of the 450-700 nm photodissociation dynamics of NCNO, 1-3 ͑CH 3 ͒ 3 CNO, 4,5 HNO, 6 CF 3 NO, 7-13 CF 2 ClNO, 14 CFCl 2 NO, 15 and C͑CH 3 ͒ 2 ClNO [16][17][18] have been reported and a general picture of the gas phase photofragmentation mechanism of nitrosoalkanes has emerged. In this wavelength range the absorption is assigned to a S 1 Ã 1 AЉ←S 0 X 1 AЈ͓n(N),*(NϭO)͔ transition.…”

“…The T 1 surface is believed to have a po-tential barrier along the dissociation reaction coordinate and dissociation across this barrier deposits a significant amount of the excess energy in product translational recoil and rotational excitation of the NO product. 16,17,21 Measurements of photoproduct trajectory -v-j angular correlations of a wide range of systems have demonstrated the power of vector correlation measurements in understanding reaction mechanisms. 16,20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Both semiclassical [40][41][42] and fully quantum mechanical [43][44][45][46][47] theories have been used to extract vector correlations from experimental data.…”

New Laser-Based and Imaging Methods for Studying the Dynamics of Molecular Collisions

“…[112][113][114][115] Another interesting application is to the dissociation of chiral molecules, where the vector correlations can, in principle, provide information about the "handedness" of rotation. [116][117][118][119][120] We will see in section VI how multiple one-dimensional techniques can be used to extract even more information from bulk sample reactions.…”