Pressure-broadening and cross-relaxation rates of rotation-inversion transitions in the nu(4) band of NH3 perturbed by CO2

Measurements of pressure-broadening and cross-relaxation rates of rotation-inversion transitions in the v(4) band (1470-1600 cm(-1)) of NH3 perturbed by CO2 are reported. Pressure-broadening parameters were measured at a low pressure of CO2 (0-180 Torr). At high pressure, the two lines of the doublet broaden as the pressure is increased, but with a markedly lower rate than at low pressure, until they overlap. Such an effect is due to collision cross-section relaxation between the two lines of the inversion components of the doublet. Detailed modeling of the spectral lines permits us to determine pressure-broadening coefficients for 41 transitions, and cross-relaxation parameters for 10 doublets. The results show a decrease of the pressure-broadening parameters with the J quantum number. We compared our results with other previous measurements obtained in the far-infrared and v(2) regions, and for several foreign gases such as He, H-2, and N-2. (C) 1996 Academic Press, Inc.