The role of spin\u2013orbit effects in the mobility of N+ ions moving in a helium gas at low temperature

Lamia Aïssaoui,Moncef Bouledroua,Peter J Knowles

doi:10.1140/epjd/e2020-10138-0

Lamia Aïssaoui, Moncef Bouledroua + Show 1 more

Open Access

https://doi.org/10.1140/epjd/e2020-10138-0

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Abstract

The mobility of N+ ions in ground-state helium gas at very low temperature is examined with explicit inclusion of spin–orbit coupling effects. The ionic kinetics is treated theoretically with the three-temperature model. The N+–He interaction potentials, including spin–orbit coupling, are determined using high-level ab initio calculations. Then, the classical and quantal transport cross sections, both needed in the computation of the mobility coefficients, are calculated in terms of the collisional energy of the N+–He system. The numerical results, at temperature 4.3 K, show the spin–orbit interactions have negligible effect on the mobility coefficients.Graphical abstract

Highlights

Ion mobility experiments in cooled buffer gases have long been of interest [1]
There have been many advances in the kinetic theory of ion mobility, such as the three-temperature (3T) theory [1], and they have reached the point where the mobility of atomic ions in cooled buffer gases can be calculated with ab-initio methods of higher accuracy than can be measured [3]
We describe the ab initio method employed in the generation of the potential-energy curves of the diatomic system correlated with the ground N+ 2s22p2; 3P state that interacts with the ground He 1s2; 1S including the effects of the spin–orbit interactions

Summary

Introduction

Ion mobility experiments in cooled buffer gases have long been of interest [1]. They are relevant in analytical chemistry, because various large ions can have quite different ion mobilities even if they have the same molar masses. We use three-temperature theory and the obtain the quantal transport cross sections with the inclusion of the spin–orbit effects to explore theoretically the causes of the unusual behaviour and peculiar shape of the N+ ion mobility in a cooled buffer gas made exclusively of ground helium at the very low temperature 4.3 K. We report the details of the present calculations of the N+–He interaction potentials that arise from the lowest atomic asymptotes of the openshell N+ 3PJ + He 1S0 system, the quantal and classical transport cross sections, and the mobility variations with electric strength, as implemented in the Fortran codes pc.f90 and gc.f90 of Viehland [9]. With the basis-set described above, the CI dipole polarizability of He is 1.382; for representing

P2 3 Π1

Diffusion cross sections

Quantal cross sections

Classical cross sections

Average cross sections

Mobility results and discussion