Changes in the Vibrational Population of SO(³Σ^-) from the Photodissociation of SO₂ between 202 and 207 nm

Abstract

Resonance-enhanced multiphoton ionization with time-of-flight product imaging has been used to study the SO 2 + hν f SO( 3 Σ -) + O( 3 P 2 ) channel in the ultraviolet photodissociation of sulfur dioxide at photolysis wavelengths between 202 and 207 nm. These imaging experiments allowed the determination of the vibrational populations of the SO( 3 Σ -) fragment at several wavelengths. A change in the vibrational populations occurs from a distribution where most of the population is in V ) 0 for wavelengths shorter than 203.0 nm to one where the population is more evenly distributed for longer wavelength dissociation. The changes in the internal energy distribution are attributed to participation of two different predissociation mechanisms. Our data suggest that the predissociation mechanism below 203.0 nm involves an avoided crossing with the repulsive singlet state 1 A 1.

O(3PJ) Alignment from the Photodissociation of SO2 at 193 nm

“…Similar structure has been observed previously at 193 nm in the TOF experiments of Kawasaki and Sato 16 and Huber and co-workers 15,37 and in the wavelength range of 202-207 nm by Houston and co-workers. 11 To estimate the SO vibrational populations, we fit the speed distributions shown in Figure 4 with a sum of Gaussian functions, each corresponding to the SO cofragment born in a different vibrational state. The widths of the Gaussians, together with the vibrational populations for levels V′ ) 0-5, were used as adjustable parameters in the fit.…”

Dissociative Recombination of \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \Declar

“…Braatz & Tiemann (1998) observed a predissociation of SO 2 into SO and O already at the relatively low C 1 B 2 level. Another photodissociation study (Cosofret et al 2000) strongly suggested that this process involves an avoided crossing with a repulsive 1 A 1 state leading to SO þ O if excited vibrational levels of the C 1 B 2 state are reached. Therefore, channel (5a) can possibly proceed following a direct mechanism via a doubly excited state.…”

A chirped-pulse Fourier-transform microwave/pulsed uniform flow spectrometer. II. Performance and applications for reaction dynamics

“…The dominant process is thought to be internal conversion arising when mixing occurs between the quasibound continuum of theX ground state with vibronic levels in theC state, but dissociation via a triplet surface could also result from the crossing of theC state by repulsive 2 3 A or 3 1 A states. 24,25,27,30 These conclusions were drawn, in part, from the observation of inverted vibrational distributions in the SO fragment, where >50% of the population is in the v = 2 vibrational level rather than the ground v = 0 state (Table I). 24,26,27,31 The CPUF spectrometer was used to probe the nascent vibrational distribution of SO following photodissociation of SO 2 .…”

“…17,[24][25][26][27][28][29] From those experiments, it was concluded that this reaction occurs via excitation from the ground X 1 A 1 state to theC 1 B 2 state followed by dissociation. However, theC state correlates diabatically to singlet fragments, SO (a 1 ) and O ( 1 D), rather than the observed triplets, SO (X 3 − ) and O ( 3 P), so other pathways must participate.…”