Dynamics of OH (X²Pi , 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 from X 2 Pi (v'=1 from v"=0) transition at 282 nm while emission at 309 nm from A 2 Sigma to X 2 Pi (v'=0 to v"=0) band, was observed. The discharge peak current I 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 I max >or=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.