Temperature-dependent line shift and broadening of CO infrared transitions

The temperature dependence of lineshift and broadening of the rovibrational transitions R(18) and X(20) of the CO fundamental band, perturbed by Ar, N -2, O-2, and H-2, have been measured with high frequency accuracy and at te mperatures between 160 and 270 K in steps of 20 K. A wavelength stabilized tunable diode laser spectrometer has been combined with a low temperature l ong path cell of 134 m absorption length and 1 m basis length. For all meas urements the CO pressure was below 0.1 mbar to avoid self-shift and self-br oadening. In case of Line broadening the temperature dependence is quite we ll reproduced by an exponential relation, b(T) = b(T-0)(T/T-0)(-n). For all foreign gases, the exponent n has been obtained (0.53 less than or equal t o n less than or equal to 0.71) and a value for air has been calculated fro m the weighted mean values of N-2 and O-2. Within the error Limits the magn itudes of all shifts decrease with increasing temperatures, but there is no exponential behavior of the shift versus temperature. The line broadening and shift for CO with Ar and the broadening of CO by N-2 and O-2 have been compared to calculations from the semi-classical theory of Robert and Bonam y. Sufficient agreement has been achieved for the line broadening, while th e calculated shifts are for all temperatures larger than the measured value s. (C) 1998 Academic Press.