A general model for the spectral calculation of OH radiation in the ultraviolet

A spectroscopic/collisional-radiative model is presented that permits the c alculation of OH(A(2)Sigma + - X(2)Pi) spectra in the ultraviolet for a wid e range of gas dynamics conditions, including those observed in hypersonic flows. This requires a rotational-vibrational-electronic excitation model s ufficiently general to account for the diversity of collision rates that en compasses conditions ranging from equilibrium to collisionless regimes. To this end, the proposed excitation model considers several state-specific pr ocesses, including quenching, predissociation, radiation, and vibrational-r otational exchange. Although the structure of the OH (A-->X) spectra is com plex, accurate line positions and transition probabilities are available an d have been used. This paper discusses the full excitation and spectral mod el and provides examples that demonstrate its generality. Detailed comparis ons are presented with experimental spectra measured under very different c onditions. The first spectrum was measured at atmospheric pressure in a pla sma generated by a 50 kW radio-frequency plasma torch. The second spectrum was measured under rarefied conditions in the bow shock of a reentering roc ket. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.