INFRARED SPECTROSCOPY OF THE $CO_{2}-D(H)Br$ COMPLEXES: LOCATION OF THE HYDROGEN ATOM
Loading...
Date
1990
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Vib-rotational spectra of $CO_{2}-HBr$ and its deuterated counterpart have been recorded utilizing the $CO_{2}$ asymmetric stretch $(2349 cm^{-1})$ chromophore. These weakly bonded dimers are created by supersonic expansion of a seeded carrier gas $(1\% CO_{2}, 1\% HBr in ArNe)$ through a pulsed slit nozzle $(.15 \times 38 mm^{2})$. Direct absorption spectra are obtained by passing the output of a tunable diode laser through the expanding effluent and monitoring laser attenuation as a function of laser frequency. Rapid tuning of the diode laser allows a complete spectrum $(\sim.75 cm^{-1})$ to be obtained during each pulse of the nozzle. As in our previous work on $CO_{2}-HBr.^{1} CO_{2}-DBr$ also exhibits spectral features associated with an asymmetric rotor. In all, 68 transitions were assigned $(K_{a}=0, 1 and 2)$ and fit to a Watson type Hamiltonian. Due to efficient rotational cooling, characteristic in supersonic expansions, only transitions up to $J=12$ and $K_{3}=2$ was available; hence only the rotational constants A, B, C. and DJK were determined for both the vibrational ground and excited states. A combination-difference method was used to obtain vibrational ground-state constants, which were then fixed for subsequent fitting of the upper-state constants as well as the band origin. $v_{0}$. Results from the two isotopically different experiments allows us to determine the distance of the H(D) atom from the center of mass of $CO_{2}-H(D)Br$. In addition, the angle between the H(D)Br molecular axis and the center-of-mass line is estimated as $\sim$. Substantial differences of the hydrogen location in bent $CO_{2}-H(D)Br$ vs. linear $CO_{2}-H(D)Cl$ and linear $CO_{2}-H(D)F$ have important ramifications for the interpretation of precusor-geometry-limited photoinitiated reactions such as $H + CO_{2} \to CO + OH$, which will also be discussed in the following talk
Description
$^{1}$ S.W. Sharpe, Y.P. Zeng. C. Wittig, and R.A. Beaudet, J. Chem, Phys. 92,943(1990).
Author Institution: Department of Chemistry, University of Southern California
Author Institution: Department of Chemistry, University of Southern California