The UV photodissociation dynamics of ClO radical using velocity map ion imaging

Abstract

We have studied the wavelength-dependent photodissociation dynamics of jet-cooled ClO radical from 235 to 291 nm using velocity map ion imaging. We find that Cl(2P(3/2))+O(1D(2)) is the dominant channel above the O(1D(2)) threshold with minor contributions from the Cl(2P(J))+O(3P(J)) and Cl(2P(1/2))+O(1D(2)) channels. We have measured the photofragment angular distributions for each dissociation channel and find that the A 2pi state reached via a parallel transition carries most of the oscillator strength above the O(1D(2)) threshold. The formation of O(3P(J)) fragments with positive anisotropy is evidence of curve crossing from the A 2pi state to one of several dissociative states. The curve crossing probability increases with wavelength in good agreement with previous theoretical calculations. We have directly determined the O(1D(2)) threshold to be 38,050+/-20 cm(-1) by measuring O(1D(2)) quantum yield in the wavelength range of 260-270 nm. We also report on the predissociation dynamics of ClO below the O(1D(2)) threshold. We find that the branching ratio of Cl(2P(3/2))/Cl(2P(1/2)) is 1.5+/-0.1 at both 266 and 291 nm. The rotational depolarization of the anisotropy parameters of the Cl(2P(3/2)) fragments provides predissociation lifetimes of 1.5+/-0.2 ps for the 9-0 band and 1.0+/-0.4 ps for the 8-0 band, in reasonable agreement with previous spectroscopic and theoretical studies.

Photodissociation of the BrO radical using velocity map ion imaging: Excited state dynamics and accurate D(BrO) evaluation

“…21,22 Briefly, a collimated molecular beam was intersected at 90°by two copropagating linearly polarized laser beams. 21,22 Briefly, a collimated molecular beam was intersected at 90°by two copropagating linearly polarized laser beams.…”

“…The bromine atoms, Br͑ 2 P 3/2 ͒ and Br͑ 2 P 1/2 ͒, were probed using 2 + 1 resonance-enhanced multiphoton ionization ͑REMPI͒ transitions at 266.650 nm ͑3p 2 P 3/2 → 4p 4 P 3/2 ͒ and 266.713 nm ͑3p 2 P 1/2 → 4p 4 S 3/2 ͒, respectively. 21 The temperature of the heated nozzle is controlled by a currentregulated power supply and maintained at approximately 600 K. Details of the source and demonstration of the performance can be found elsewhere. 24 The resultant Br and O cations were accelerated by velocity mapping electrostatic lenses prior to entering the 50 cm long field-free flight tube coaxial with the molecular beam.…”

“…Although the speed distributions derived from the Br͑ 2 P J ͒ and O͑ 3 P J ͒ fragment images at 354.7 nm can, in principle, provide direct measures of D 0 0 ͑BrO͒ based on Eq. 21,33 We are able to reproduce both the magnitudes and speed dependence of the anisotropy parameter assuming a rotational temperature of 150 K and a JЉ-independent intrinsic anisotropy parameter of 1.8± 0.2. In order to reduce the uncertainty associated with the measurement, we sought to observe the low velocity Br͑ 2 P 3/2 ͒ +O͑ 1 D 2 ͒ photofragments arising from photodissociation just above the A 2 ⌸ 3/2 state dissociation threshold.…”

Ion imaging studies of ClONO2 photodissociation: Primary branching ratios and secondary dissociation

“…nately Cl( 2 P 3/2 ) + O( 1 D 2 ) with an anisotropy parameter of 1.8 ± 0.1 [30]. We assume, therefore, that the Cl( 2 P 1/2 ) image is dominated by chlorine atoms originating from channel 1.…”

An ab initio investigation on the ground electronic state of chlorine monoxide and its singly charged cation and anion

“…Thereafter, a variety of experimental techniques have been performed to study ClO, including methods of flash photolysis [8][9][10] spectroscopy [11], microwave spectroscopy [12][13][14][15], ultraviolet spectroscopy [16,17], matrix isolation [18], laser magnetic resonance spectroscopy [19], infrared spectroscopy [20,21], multiphoton ionization spectroscopy [22,23], laser-induced fluorescence spectroscopy [24], resonance-enhanced multiphoton ionization [25][26][27] and velocity-map ion-imaging [28][29][30]. Efforts have also been made on the accompanying theoretical analyses [31][32][33][34][35][36].…”