Mobility and diffusion of atomic helium and neon ions in their parent gases

Abstract

The mobility and the diffusion tensor have been calculated for He+ ions in He and Ne+ ions in Ne, at temperatures of 77-78 and 294 K, and at field-to-density values E/no up to 2000 Td. For He+ ions in He, ab initio potentials were used, with a careful extrapolation to large distances. A slight adjustment of the mean potential resulted in agreement between calculated mobilities and the best experimental values to better than 0.5%. For Nef ions in Ne, a potential model with three adjustable parameters was constructed, and an overall agreement between measured and calculated mobilities to better than 1 was obtained. The model potentials probably give a good estimate of the gerade-ungerade splitting at internuclear distances from 7.5 to 10 au, but are not expected to be accurate at shorter distances .

Transport coefficients of He+ ions in helium

“…18. The results were in good agreement with the values obtained by Sinha et al 30 using a 2T kinetic theory. Unfortunately, both sets of results are based on calculations that started by assuming that and are the same and that the ion velocity distribution function does not show skewness, kurtosis or the correlations that are present in the GC kinetic theory used here.…”

“…To obtain additional information, we considered a pair of potentials for He 2 + that had been "tuned" 30 believe the present results to be more accurate than the prior semi-classical results for this tuned potential.…”

“…We used QEx to calculate the semi-classical cross sections to 0.04% and then used GC to compute the same mobilities with a precision of 0.04%. It was expected 18,30 that the quantum-mechanical values would lie below the semi-classical values, but the differences shown in Fig. 5 allow us to quantify this: quantum-mechanical effects lower the mobilities of 4 He + in 4 He near room temperature by the ratio…”

“…There have been many other calculations of the PECs for He 2 + over the years [24][25][26][27][28][29][30][31][32] , with the results improving as better algorithms and faster computers became available. Lee 33 reviewed the work up until 1993, and then presented CASSCF+MRCISD calculations (denoted CAS+MRCI hereafter), concluding that the potentials he produced for the X 2  u + and A 2  g + states were reliable and close to what could be expected with full CI calculations; it was acknowledged, however, that the study was limited by the range of basis sets that could be employed.…”

Theoretical calculation of transport properties of the noble gases He and Ne and their binary mixtures at low density

“…Alternatively, we can use the dispersion coefficients and the experimentally measured well depth and the location of the well minimum R,, to determine the Born-Mayer parameters A and b (Tang and Toennies, 1978). The modified Tang-Toennies model can predict the potentials for ion-atom systems (Ahlrichs et al, 1988;Skullerud and Larsen, 1990).…”