Velocity distributions of He⁺, Ne⁺and Ar⁺in parent gases

Abstract

Measurements are made of the velocity distributions of He+, Ne+ and Ar' ions drifting in their respective parent gas under the action of a uniform electric field at room temperature (297-300 K). Considerable improvements have been implemented in the present apparatus in comparison with older systems. The drift tube is greatly enlarged and its pressure accurately controlled by a regulating servo-valve. A new ion optical system coupled with a wider quadrupole analyser head ensures a high collection efficiency of ions transmitted through the retarding potential grids. A novel in-drift obstacle and a 90" off-axis detector effectively suppress interference from uv photons and metastable species. Experimental results for E / N ranging from 60 to 320 Td are compared with both the Wannier equation for the RMS ion velocity and the corresponding Maxwellian distribution. The typical experimental curve is found to possess only a single maximum with its peak displaced towards the low velocity end and an enhanced high velocity tail in comparison with the Maxwellian.

Resonant charge exchange and the transport of ions at high electric-field to gas-density ratios (E/N) in argon, neon, and helium

“…Mase and co-workers [13] have clearly shown from low-pressure drift-tube experiments that at sufficiently high effective EIN, the kinetic-energy distribution of Ar+ in Ar will exhibit significant deviations from Maxwellian behavior with a high-energy tailor peak indicative of "runaway" or "beamlike" ions that experience few if any collisions in traversing the drift tube. It should be noted that departures from Maxwellianbehaviorhave also been seen for He+ in He, Ne+ in Ne, and Ar+ in Ar from the measuredionvelocity distributions of Ong and Hogan [14] for relatively low EIN, below 3.2X 10-19 V m2 (320 Td). At low EIN, the .Permanent address:Institutefor PlasmaResearch, Bhat,Gandhinagar, 382424 India.…”

“…The relative contributions to the total flux of ions hitting the cathode from the doubly charged species Ar2+, Ne2+, and He2+ were estimated at each E/N using Eqs. (12)- (14). The results are given in Tables IV-VI together with estimated uncertainties (typically less than :::!…”

Ion kinetics and symmetric charge-transfer collisions in low-current, diffuse (Townsend) discharges in argon and nitrogen

“…Velocity distributions of Ar+ in Ar have been measured by Ong and Hogan [18) in a uniform-field drift tube for electric field-to-gas density ratios (EIN) up to 1063-65lX/95/5 1(6)/6036(11)/$06.00 3.2 X 10-19 Vm2 (320 Td). They found that the measured distributions showed increasing deviations from a Maxwellian distribution as E IN was increased.…”

“…Makabe and Shinada [22) have pointed out difficulties with the ion sampling procedures used in drift-tube experiments such as those performed by Ong and Hogan [18), which can lead to distortions in measured ion- 51 6036 @1995 The American Physical Society velocity distributions. Lin and Bardsley [23] had previously argued that differences between measured and calculated ion-velocity distributions are probably due to effects of discrimination in the experimental sampling.…”

Vibrational relaxation in the NO+–He collision system: Implication of the Gislason–Ferguson model

“…͒ increases, the form of the distribution function will deviate from the Maxwellian one. The results of Monte Carlo simulations [55][56][57] indicate that at KE c.m. values corresponding to Tϭ2000-3000 K this deviation becomes substantial, thus, also influencing significantly the results when converting reaction cross sections into rate constants.…”