Laser Probing of Rotational-State-Dependent Velocity Distributions of N+2 (Ņ= O,J) Drifted in He
E B. Anthony, V M. Basitan, V M. Bierbaum, S R. Leone
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 Ko(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.
Journal of Chemical Physics
Doppler, drift, ion, laser, mobility, velocity
, Basitan, V.
, Bierbaum, V.
and Leone, S.
Laser Probing of Rotational-State-Dependent Velocity Distributions of N<sup>+</sup><sub>2</sub> (Ņ= O,J) Drifted in He, Journal of Chemical Physics
(Accessed December 3, 2023)