Collisional deexcitation of metastable ions: A new technique to separate radiative and nonradiative contributions AIP Conf.Radiative lifetimes and bimolecular rates have been determined for two-photon laser excited states ofXe* (5p 5 6p, 5p 5 6p', 5p 5 7p) in argon and xenon buffer gases. The collisional deactivation rates are found to be very large for the Xe 6p' and 7p states [-(2-5) X lO-1O cm3/s] while the rates for the Xe 6p states are comparatively smaller [-(0.06-1.2) X lO-1O cm 3 /s]. In general, the quenching rates in argon are about a factor of 2 smaller than the xenon quenching rates for the same excited state with the notable exception ofXe 6p[ 112]0' For Xe 6p [ 112] 0' a multicomponent decay has been observed in argon buffer gases. The second component is attributed to collisional coupling to Xe 5d[ 112] 1 which lies 132.3 cm -I below Xe 6p [ 112] 0' Quench rates determined from the collisionally induced VUV fluorescence from Xe 5d[ 112] 1 at 125 nm are in excellent agreement with this assignment. Furthermore, these experiments have unambiguously identified the product channel involved in the curve crossings observed in studies of optical collisions [N.
Lifetimes and bimolecular quenching rate constants have been determined for two-photon laser excited states of Xe*(5p56p,5p56p′,5p57p) and Kr*(4p55p) in krypton and xenon buffer gases. Collisional mixing between Kr*5p[5/2]2 and Kr*5p[5/2]3 in krypton is observed and analyzed using a coupled two-state model to obtain the rate of mixing. The measured rate constants for quenching of Xe*(6p′,7p) by krypton are 15%–20% smaller than those measured previously in xenon while bimolecular rates for the Kr*(5p) states are an order of magnitude larger in xenon than those in a krypton buffer. Measurements of state-to-state rate constants for deactivation and excitation transfer are also reported for these states in krypton and xenon buffer gases.
Highly sensitive detection of neutral Kr atoms was accomplished by the use of laser-induced fluorescence. In one experiment, Kr at 40 parts per 10(12) in He was detected at a signal-to-noise ratio of 500 by time-resolved fluorescence measurements. The Kr metastable 1s(5) level was populated by cascade after two-photon excitation to the 2p(6) level by the frequency-tripled output of a pulsed single-longitudinalmode dye laser. After a delay, when scattered laser light and cascade resonance fluorescence became negligible, trace quantities of Kr were detected by the use of a pulsed-laser pumping scheme. In a related experiment, (78)Kr/(86)Kr isotope ratios ranging from 1 to 0.1 were measured with a resonant isotopic depletion technique first proposed by Makarov [Sov. J. Quantum Electron. 13, 722 (1983)]. The (86)Kr metastable population was selectively depleted by optical pumping to a higher-lying state that relaxed to the ground state by means of radiative cascade. After the (78)Kr/(86)Kr ratio of metastables had been enriched by a factor of 10, the (78)Kr population was probed by pulsed excitation. Premixed (78)Kr/(86)Kr ratios were measured to within an accuracy of 10%, even for unresolved, Doppler-broadened transitions.
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