Collisional relaxation of ionic2 P 3/2 excited states in rare gases

Measurements of ion velocity distributions are presented for Ba+ drifted in helium under well characterized conditions using single-frequency laser-induced fluorescence probing. We present the reduced mobilities and the Doppler profiles parallel and perpendicular to the electric field vector as a function of the ratio of the field strength (E) to the buffer gas density (N) up to 33.5 Td. The reduced mobility decreases monotonically with increasing E/N from the zero-field value of 16.7±0.4 cm2 V−1 s−1 at 313 K. The parallel and perpendicular ion temperatures are in very good agreement with both a repulsive Maxwell model and a parametrized version of the three-temperature theory of Lin et al. The parallel temperature is always higher than the perpendicular one. Effects of optical pumping on the Doppler profiles are also presented.

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Laser-induced fluorescence measurements of drift-velocity distributions for Ba+ in Ar: Moment analysis and a direct measure of skewness

Penn

Beijers

Dressler

et al. 1990

The Journal of Chemical Physics

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Velocity distributions for Ba+ ions drifting in argon under the influence of an electric field are measured using single-frequency, laser-induced fluorescence techniques. A moment analysis of these data yields values for the ion mobilities, temperatures, and, for the first time, skewness parameters of the ion velocity distributions. Doppler profiles of the drifting ions are obtained with the laser beam propagating both parallel and perpendicular to the electric field direction as a function of E/N up to 148 Td. The velocity-component distributions perpendicular to the electric field direction are nearly Maxwellian at all E/N values studied, but the parallel distributions become noticeably skewed toward high velocities at the largest electric field strengths. The reduced mobilities for Ba+ in Ar, obtained from the first moments of the parallel velocity-component distributions, increase from 1.80±0.16 cm2 V−1 s−1 at zero field to 2.38±0.11 cm2 V−1 s−1 at 148 Td. The second central moments, which describe the widths of the distributions, increase monotonically with increasing E/N values for both the parallel and perpendicular distributions. Temperatures derived from the second central moments agree well with those calculated from a parametrized version of the three-temperature theory [M. Waldman and E. A. Mason, Chem. Phys. 58, 121 (1981)]. The third central moments of the parallel velocity-component distributions characterize the asymmetry of the distributions. Skewness parameters derived from the third central moments increase with electric field strength over the range of E/N studied.

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Collisional relaxation of ionic2 P 3/2 excited states in rare gases

Cited by 3 publications

References 30 publications

Steady state signal in the limit of weak optical pumping with D1 or D2 line

Steady state signal in the limit of weak optical pumping with D1 or D2 line

Laser probing of ion velocity distributions in drift fields: Parallel and perpendicular temperatures and mobility for Ba+ in He

Laser-induced fluorescence measurements of drift-velocity distributions for Ba+ in Ar: Moment analysis and a direct measure of skewness

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