In the actual version, RS assumes isothermal conditions. However, if the reduced electric field strength (the electric field divided by the number density) becomes high (a couple of Td), the kinetic energy ions gain from the electric acceleration becomes higher than the thermal kinetic energy. This effect can be modeled by a field dependent ion temperature which can readily become very high, in particular in reduced background pressure regimes.

In the last months, we have extended RS with an basic ion temperature model, presented in great detail in the work by Mason and McDaniel[1] or more recently in the first paper of a series about ion dynamics by Viehland and Siems[2].

On the annual meeting of the ASMS in Minneapolis this year, we presented this model and some examples of simulations with the modified RS code on a Poster: “Field driven chemical effects in API: Numerical modeling of the ion temperature at atmospheric and intermediate pressure with SIMION-RS”

Currently our plan is to update the public RS version with the (still quite experimental) ion temperature code in the next weeks. At the moment we are figuring out, in which way we can elegantly introduce the necessary information about the temperature dependence of the reaction probability into the RS configuration file.

References:

• [1] Mason, E. A.; McDaniel, E. W., Transport Properties of Ions in Gases; Wiley-Interscience: New York, 1988.
• [2] Viehland, L. a; Siems, W. F., Uniform moment theory for charged particle motion in gases. Journal of the American Society for Mass Spectrometry. 2012, 23, 1841–54. DOI: 10.1007/s13361-012-0450-7.