Temperature dependences for air-broadened Lorentz half-width and pressure shift coefficients in the 30013←00001 and 30012←00001 bands of CO2 near 1600 nm This article is part of a Special Issue on Spectroscopy at the University of New Brunswick in honour of Colan Linton and Ron Lees.

Abstract

In this study, 39 high-resolution spectra of pure and air-broadened CO2 recorded at temperatures between 215 and 294 K were analyzed using a multispectrum nonlinear least-squares technique to determine temperature dependences of air-broadened Lorentz half-width and air-induced pressure shift coefficients for over 100 individual 12C16O2 transitions in the 30012←00001 (at 6348 cm–1) and 30013←00001 (at 6228 cm–1) bands. Data were recorded with two different Fourier transform spectrometers (Kitt Peak FTS at the National Solar Observatory in Arizona and the Bomem FTS at NRC, Ottawa), with absorption path lengths ranging between 25 and 121 m. The sample pressures varied between 11 torr (pure CO2) and 924 torr (CO2-air) with volume mixing ratios of CO2 in air between ∼1.5% and 11% (1 torr = 133.322 4 Pa). To minimize systematic errors and increase the accuracy of the retrieved parameters, a constrained multispectrum nonlinear least-squares fitting technique was used to include theoretical quantum mechanical expressions for the rovibrational energies and intensity parameters rather than retrieving the individual positions and intensities line by line. The results suggest no detectable vibrational dependence for the temperature dependences for the air-broadened Lorentz half-width coefficients and the air-induced pressure shift coefficients. The half-width coefficients and temperature dependence exponents were modeled using semiclassical calculations based upon the Robert–Bonamy formalism. A good agreement is seen between the measurements and theoretical calculations. Beyond |m| = 26, a simple scaling factor (0.96) has been applied to the calculated half-width coefficients to match the experimental measurements.