Rotational collisional narrowing in an infrared CO2 Q branch studied with a tunable-diode laser

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Abstract
Rotational collisional narrowing, or line mixing, has been observed in the infrared absorption spectrum of the Q branch of the (1110,0310)II – 0000 band of CO2 at 1932.47 cm−1 using a tunable diode laser. Spectra were recorded at pressures ranging from 100 to 745 Torr both inside the Q branch and below the band origin. The observed absorption coefficients below the band origin were up to 80% less than those calculated using an isolated Lorentz line approximation. A simple fitting law for the state-to-state rotationally inelastic rate constants is determined using the known line broadening coefficients. A calculation of line mixing using these rates agrees with the observed absorption coefficients to within several percent.