Testing ion-neutral interaction potentials using calculated ion transport coefficients

Abstract

Several commonly measured ion transport coefficients were investigated in order to determine their sensitivity for testing and comparing proposed ion-neutral interaction potentials. A variety of positive ions, negative ions, neutrals, and temperatures were included in order to draw as general a conclusion as possible. All transport coefficients considered were found to be sufficiently sensitive to be used to clearly distinguish between less and more accurate interaction potentials. It was also found that the longitudinal diffusion coefficient is the most sensitive test, followed by both the transverse diffusion coefficient and the ratio of the longitudinal diffusion coefficient to mobility, followed by the ratio of the transverse diffusion coefficient to mobility and that the mobility is the least sensitive test. When presently achievable levels of experimental error were also taken into account, however, there was no significant difference in the sensitivities.

Experimental measurement of the mobilities of atomic and dimer Ar, Kr, and Xe ions in their parent gases

“…3 In gaseous radiation detectors used in nuclear and particle physics it is known that the motion of the ions plays a very important role in the pulse formation. In ion mobility spectrometry 1 molecules are identified by measuring their ionic velocity in a gaseous atmosphere.…”

Transport coefficients of He+ ions in helium

“…Although it has been shown 72 that it is better to use diffusion data if both have the same experimental accuracy, mobility values are more easily determined in drift tubes and tend to be more accurate. In a drift-tube experiment one usually infers the ion mobility, , and the standard (or reduced) ion mobility, , from the average ion speed, often called the drift velocity, using the equations…”

Interaction potentials, spectroscopy and transport properties of RG+–He (RG=Ar–Rn)

“…The data at 82 K are in reasonable agreement with the calculations for both states, owing to our choice again to use 4% for the accuracy, a value that was not reported by the experimenters. 28 The data near room temperature are not in good agreement with the calculations, suggesting that those data may be even less accurate than the estimate of 5% made by the experimenters 27 .…”

“…Such studies can, if there are enough data points, and if the accuracy and precision are high enough, provide stringent tests of potentials across a very wide range of internuclear separation. 27 To this end, we have calculated mobilities using both the MAL1 and the present potentials, and have compared the results to experimental data. In Figure 3, the results at 300 K are given, both those calculated from the present potentials and the experimental data points.…”

“…24 At present, the fitted (MAL1) interaction potential reported in that work (similar to that obtained for Ar + -He, mentioned above) represents most of the information that is known for this species. 27 Generally, such tests are more stringent than comparison with spectroscopic data, as the latter usually only sample a very small region of internuclear separation. One of the present species is an exception, however, since spectroscopic data close to the minimum, 4 as well as at very long range 6 are available for Ar + -He.…”