Semi-empirical scaling for ion–atom single charge exchange cross sections in the intermediate velocity regime

Abstract

We present a semi-empirical scaling law for non-resonant ion-atom single charge exchange cross sections for collisions with velocities from 10 to 10 cm s 7 9 1and ions with positive charge q 8 < . Non-resonant cross sections tend to have a velocity peak at collision velocities v 1 au  with exponential decay around this peak. We construct a scaling formula for the location of this peak then choose a functional form for the cross section curve and scale it. The velocity at which the cross section peaks, v m , is proportional to the energy defect of the collision, E D , which we predict with the decay approximation. The value of the cross section maximum is proportional to the charge state q, inversely proportional to the target ionization energy I T , and inversely proportional to v m . For the shape of the cross section curve, we use a function that decays exponentially asymptotically at high and low velocities. We scale this function with parameters v I Z Z , , , and m T T P , where the Z T,P are the target and projectile atomic numbers. For the more than 100 cross section curves that we use to find the scaling rules, the scaling law predicts cross sections within a little over a factor of 2 on average.

A gas cell apparatus for measuring charge exchange cross sections with multicharged ions

“…[12][13][14], but given the vast number of possible interesting combinations a drive to develop scaling relationships also continues. 15 In the case of multicharged ions (MCIs) (q > 1), the transferred electron can be captured into an excited state of the ion (especially in the case of q 1) and the charge exchange is inferred by the detection of a photon(s) from the relaxation a) Electronic mail: sjbroml@clemson.edu b) Electronic mail: jmarler@clemson.edu process. 16 Laboratory observations of MCIs require an Electron Beam Ion Source (EBIS) or a similar apparatus.…”

Atomic iron and nickel in the coma of C/1996 B2 (Hyakutake): production rates, emission mechanisms, and possible parents

“…Ion impact experiments of iron carbonyl (Indrajith et al 2019) indicate Fe + energies post-fragmentation between 0.1 -1 eV (0.6 -1.9 km/s). At these low energies the cross section for charge exchange is likely small, < 10 −17 cm 2 (see Friedman & DuCharme (2017) and references therein). For a nominal neutral density in the inner coma of 10 10 cm −3 , the mean free path for charge exchange is in order 10 4 km, too large to explain the observed spatial profiles.…”

Charge Exchange Cross Sections for Noble Gas Ions and N2 between 0.2 and 5.0 keV

“…However, cross sections for reactions with a large ∆E may become significant in certain high collision energy regions. When reactant B is a molecule, the number of possible reaction channels is large compared to the atomic case, and the energy dependence of the charge exchange cross section deviates from the single-peaked structure seen in asymmetric reactions such as those compiled by [15]. This is illustrated in particular by collisions between N 2 and atmospheric ions H + and O + in the summary of [7].…”