Collisional broadening of rotation–vibration lines for asymmetric-top molecules. II. H2O diode laser measurements in the 400–900 K range; calculations in the 300–2000 K range

Abstract

Numerous comparisons between predictions of the model presented in part I of this paper and experimental H2O infrared linewidths are presented. It is shown that our model, contrary to those used up to now, gives accurate results for H2O room-temperature line broadening by O2 and Ar, and for high rotational quantum-number lines by N2. First accurate experimental widths and intensities of some H2O ν2-band lines in the 400–900 K temperature range are also presented. Detailed analysis of the data demonstrates the great influence of a ‘‘resonance overtaking’’ mechanism. The latter results from the modifications of both the perturber rovibrational population distribution and kinetic energy with temperature; it strongly enhances the contributions of the collision-induced rotational transitions involving significant energy jumps. This mechanism is well accounted for by our model and quantitatively explains the unusually slow decrease of some linewidths with temperature.