DYNAMICS OF OH (X(2)PI, V=0) IN HIGH-ENERGY ATMOSPHERIC-PRESSURE ELECTRICAL PULSED DISCHARGE

Time transients of the number density of the hydroxyl radical ground state X(2) Pi (v = 0) formed in the Dc high-energy atmospheric pressure pulsed discharge were measured by means of laser-induced fluorescence. The frequency doubled dye laser was tuned to the A(2) Sigma <-- X(2) Pi (v' = 1 <-- v'' = 0) transition at 282 nm while emission at 309 nm from A(2) Sigma --> X(2) Pi (v' = 0 --> v'' = 0) band, was observed. The discharge peak current l(max) varied from 10(-2) to 10 A, and the time duration was from 500 ns to 50 mu s. The discharge was operated at repetition rate of 10 Hz. The population of v'' = 0 of OH reaches the steady state within the first 20 mu s of the discharge and its value is independent on the current for l(max) greater than or equal to 0.2 A. The significant build-up of v'' = 0 state population was observed after the discharge pulse. The hydroxyl ground state number density reaches its maximum value approximately 100 mu s after the discharge and is up to three times larger than during the discharge pulse. This increase of v'' = 0 population is attributed to the vibrational relaxation within X(2) Pi state.