LASER SPECTROSCOPY AND DYNAMICS OF THE JET-COOLED AsH$_2$ FREE RADICAL
Loading...
Date
2007
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
The $\tilde{A} ^2{A}_1$ - $\tilde{X} ^2{B}_1 }$ electronic transition of the jet-cooled AsH$_2$ free radical has been studied by laser-induced fluorescence (LIF), wavelength-resolved emission, and fluorescence lifetime measurements. The radical was produced by a pulsed electric discharge through a mixture of arsine (AsH$_3$) and high-pressure argon at the exit of a pulsed valve. Nine vibronic bands were identified by LIF spectroscopy in the 505-400 nm region, including a long progression in the bending mode and two bands ($1_0^1$ and $1_0^1$$2_0^1$) involving the excited state As-H symmetric stretch. Single vibronic level emission spectra showed similar activity in the bending and symmetric stretching frequencies of the ground state. High- resolution spectra of the $0_0^0$ band exhibited large spin-splittings and small, resolved arsenic hyperfine splittings, due to a substantial Fermi contact interaction in the excited state. The rotational constants obtained in the analysis gave effective molecular structures of $r_0^{\prime \prime}$ = 1.5183(1) \AA, ${\theta}_0^{\prime \prime}$ = 90.75(1)$^o$ and $r_0^{\prime }$ = 1.4830(1) \AA, ${\theta}_0^{\prime }$ = 123.10(2)$^o$. The excited state fluorescence lifetimes vary dramatically with rovibronic state, from a single value of 1.4 $\mu$s to many with lifetimes less than 10 ns, behavior which we interpret as signaling the onset of a predissociative process in the excited state.
Description
Author Institution: Institute of Chemistry, Chinese Academy of Sciences, Zhongguancun, Beijing 100080, P.R.C.; Department of Chemistry, University of Kentucky, Lexington, KY 40506-0055