Direct Measurements of Line-Mixing Coefficients in the nu1 + nu2 Q Branch of CO2.

High-resolution measurements of the (nu1 + nu2) Q branch of pure CO2 were made using a difference frequency spectrometer with resolution of 5 x 10(-5) cm-1 and a signal-to-noise ratio of 2000:1. Lines Q(2) through Q(32) were measured with up to 14 lines in a single spectrum. The analysis of the branch has been performed on data taken at 301 K and pressures less than 11 kPa. The spectra were analyzed on a line-by-line basis within the Rosenkranz approximation of weak overlap [P. W. Rosenkranz, IEEE Trans. Antennas Propagation AP-23, 498 (1975)]. The lineshape profile included Doppler broadening and Dicke narrowing [R. H. Dicke, Phys. Rev. 89, 472 (1953)] using a modified hard collision model [S. G. Rautian and I. I. Sobel'man, Sov. Phys. Uspekh. 9, 701 (1967)] with line mixing. For each line the broadening, Dicke narrowing, and line-mixing coefficients were determined. The broadening coefficients are in good agreement with measurements of lines belonging to different CO2 bands. Our measured line-mixing parameters are compared to those predicted by a relaxation matrix which was calculated from an exponential power gap (EPG) law [L. L. Strow, D. C. Tobin, and S. E. Hannon, J. Quant. Spectrosc. Radiat. Transfer 52, 281 (1994)]. The vibrational band intensity and the linear pressure shift of the branch were also measured. Copyright 1997Academic Press