CARS STUDIES OF H2O MOTIONAL NARROWING IN HIGH-PRESSURE AND HIGH-TEMPERATURE H2O-N2 MIXTURES

CARS spectra of the nu1 band of water vapour at room temperature and 2100 K over a large pressure range (200-19 x 10(5) Pa) were studied experimentally and theoretically. The influence of N2 and H2O on the rotational relaxation processes of H2O in H2O-N2 mixtures was investigated. Modelling of the CARS spectrum was performed using the relaxation matrix inversion procedure. Two rotational relaxation models based on energy and angular momentum transfer were tested and good agreement between experiment and theory was found for all the conditions studied. At 19 x 10(5) Pa and 2100 K, motional narrowing was found to be weak, allowing calculation of the CARS spectrum with the simple isolated-line model.