High-resolution coherent VUV spectroscopy of NO[C 2Π(1)∼B 2Π(10), B 2Π(11)] and CO[B 1Σ(0)

Abstract

The outputs of two single longitudinal mode dye lasers have been combined by the processes of four-wave sum and difference frequency mixing in Hg vapour to produce tunable, coherent VUV radiation in the ranges 110–116 nm and 178–195 nm, respectively. The dye laser pulses of 500 MHz bandwidth (fwhm) produced a VUV pulse of bandwidth 3 GHz (0.1 cm −1, fwhm).The bandwidth was tested by recording UF spectra of NO[B 2Π←X 2Π(10, 0) and (11, 0)] and CO[B 1Σ +←X 1Σ +(0, 0)]. This VUV light was also used to excite single rovibrational levels of NO or CO in a supersonic jet and the resulting radiative decay was monitored by time-resolved fluorescence detection. Collision-free radiative lifetimes were measured for the first time for several low J rotational levels of B 2Π(10) and B 2Π(11) of NO. The B 2Π(10) level showed a variation in lifetime of 60.6±2.0 to 39.3±5.0 ns from J = 1 2 to J = 11 2 while B 2Π(11) showed no variation in its lifetime of 14.0±0.4 ns. Linewidth measurements for the C 2Π(1) level infer a lower limit of 0.03 ns for its lifetime. Lifetimes were also measured for B 1Σ +(0) of CO whose radiative decay revealed severe radiation trapping effects at pressures above 10 −5 Torr.