Knowledge Bank

Comparisons between available room temperature infrared experimental $H2O$ line-widths and results of a recent semi-classical $model1$ developped by the authors are presented. The latter, contrarily to these generally used up to now for $H2O$ collisional-broadening, provides a satisfactory treatment of close collisions through modelings of both trajectory modifications and short-range potential contributions; these improvements are demonstrated by the accurate results obtained for $N2$-broadening of high rotational quantum number lines and for the broadenings associated to weakly $(O2)$ or non-polar (Ar) perturbers. Accurate diode-laser measurements of $H2O$ infrared line-parameters in the 400-900 K temperature range are also presented. The measured self- and $N2$-broadened widths of some high rotational quantum number lines show unusually slow decreasings with temperature. Detailed analysis of the data demonstrates the great influence of a ``resonance overtaking'' mechanism. The latter is well accounted for by our model and results from the modifications of both the velocities and perturber revibrational populations distributions with temperature.