Pressure broadening parameters of the hydroxyl radical A 2Σ+ (υ′=0)←X 2Π3/2 (υ"=0) transitions at ca.308 nm

Pressure broadening widths and pressure-induced frequency shifts for the hydroxyl radical Q(11)(1), Q(21)(1), Q(11)(2), Q(21) (2) absorption lines in the A (2)Sigma(+) (upsilon' = 0) <- X (2)Pi(3/2) (upsilon '' = 0) band at ca. 308 nm have been determined in the presence of a variety of gases (N-2, Ar, Ne and He). Hydroxyl radicals were formed using either a microwave discharge or a vacuum ultraviolet photolysis of water vapour and were detected using direct absorption spectroscopy with a bandwidth normalised noise equivalent absorption sensitivity of 5 x 10(-5) Hz(-1/2). A tunable external cavity diode laser at 835 nm and a single-frequency continuous-wave intracavity frequency-doubled diode laser at 488 nm were used to produce tunable continuous-wave light at 308 nm by sum-frequency generation in a beta-BaB2O4 crystal.