Temperature-Dependent Line Shift and Broadening of CO Infrared Transitions

The temperature dependence of lineshift and broadening of the rovibrational transitions R(18) and R(20) of the CO fundamental band, perturbed by Ar, N2, O2, and H2, have been measured with high frequency accuracy and at temperatures between 160 and 270 K in steps of 20 K. A wavelength stabilized tunable diode laser spectrometer has been combined with a low temperature long path cell of 134 m absorption length and 1 m basis length. For all measurements the CO pressure was below 0.1 mbar to avoid self-shift and self-broadening. In case of line broadening the temperature dependence is quite well reproduced by an exponential relation, b(T) = b(T0)(T/T0)−n. For all foreign gases, the exponent n has been obtained (0.53 ≤ n ≤ 0.71) and a value for air has been calculated from the weighted mean values of N2and O2. Within the error limits the magnitudes 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 N2and O2have been compared to calculations from the semi-classical theory of Robert and Bonamy. Sufficient agreement has been achieved for the line broadening, while the calculated shifts are for all temperatures larger than the measured values.