CARS studies of H2O motional narrowing in high‐pressure and high‐temperature H2ON2 mixtures

CARS spectra of the ν 1 band of water vapour at room temperature and 2100 K over a large pressure range (200-19 × 10 5 Pa) were studied experimentally and theoretically. The influence of N 2 and H 2 O on the rotational relaxation processes of H 2 O in H 2 O-N 2 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 × 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