Laser Probing of Rotational-State-Dependent Velocity Distributions of N+2 (Ņ= O,J) Drifted in He

Published

June 1, 2000

Author(s)

E B. Anthony, V M. Basitan, V M. Bierbaum, S R. Leone

Abstract

rotational state-resolved velocity component distribution functions of N⁺₂ (nu=O) drifted in helium are measured in a flow-drift apparatus by the technique of single-frequency laser-induced fluorescence (LIF). A single-mode ring dye laser is used to probe Doppler profiles of various rotational lines in the R-branch of the (Ņ' ,Ņ) =(O,O) band of the B²ς⁺_g system at 390 nm, with the laser propagation direction set either parallel or perpendicular to the drift field. A small but definite (3%) increase in ion mobility with increasing rotational state from J=13.5 to J=22.5 is observed at a fixed field strength of 12 Td Mobilities of J=15.5 measured over the range of 1.5-16 Td yield a K_o(O) of 22.0 cm²V^-1s^-1 and are in good agreement with earlier arrival-time measurements. Parallel translational temperatures are found to be significantly higher than perpendicular temperatures; a difference of at least 140 K between these temperatures is measured for J=15.5 at 16 Td. No discernible difference between the parallel translational temperatures for different rotational states is observed. There is evidence for a small degree of positive skewness(third central moment) in the parallel velocity component distributions, the first observation of such an effect in a molecular ion-atomic buffer system. Previous results that indicated poor agreement between CO⁺-He pulsed-field arrival-time and LIF mobilities are discussed: the LIF results were most likely hampered by space-charge effects.

Citation

Journal of Chemical Physics

Volume

112

Issue

No. 23

Pub Type

Journals

Keywords

Doppler, drift, ion, laser, mobility, velocity

Citation

Anthony, E. , Basitan, V. , Bierbaum, V. and Leone, S. (2000), Laser Probing of Rotational-State-Dependent Velocity Distributions of N⁺₂ (Ņ= O,J) Drifted in He, Journal of Chemical Physics (Accessed October 11, 2025)