Collisional Line Mixing in $N_{2}O$ Q Branches

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Title: Collisional Line Mixing in $N_{2}O$ Q Branches
Creators: Strow, L. L.; Pine, A. S.
Issue Date: 1987
Publisher: Ohio State University
Abstract: Rotational collisional narrowing, or line mixing, has been observed in both the $\nu_{1}+\nu_{2}$ and $\nu_{2}+\nu_{3}$ Q branches of $N_{2}O$ near 1880 and $2800 cm^{-1}$ using a difference-frequency spectrometer and a tunable diode laser spectrometer. Spectra were recorded at pressures ranging from 1 to 740 torr, all self-broadened. The observed pressure-broadened widths of Q(1) through Q(33) in $\nu_{1}+\nu_{2}$ agree with those reported by Lacome $et. al.^{1}$ for the P and R branches of the $2\nu_{1}, \nu_{1}+2\nu_{2}, 2\nu_{2}$, and $\nu_{1}$ bands to within several percent. Line-mixing effects are most evident between Q(15) and Q(1) and above the Q-branch head at pressures of 200 torr and greater. Deviations between the observed absorption coefficients and those calculated using the normal isolated Lorentz line model are as large as 50\% at 1 atm. A simple energy gap scaling law is used to model the off-diagonal relaxation matrix elements from the observed pressure-broadening coefficients. Spectra calculated from these matrix elements substantially reproduce the experimental data if it is assumed that 1/2 of all collisions place the molecule into doubled rotational states that are not accessed by the Q-branch transitions.
Description: $^{1}$ N. Lacome, A. Levy, and G. Guelachvili, Appl. Optics. 23, 425 (1984).
Author Institution: Department of Physics, University of Maryland Baltimore County; Molecular Spectroscopy Division, National Bureau of Standards
Other Identifiers: 1987-TB-14
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