Eur. Phys. J. D (2012) 66: 26
https://doi.org/10.1140/epjd/e2011-20625-x

Regular Article

Electron impact excitation of higher energy states of molecular oxygen in the atmosphere of Europa

¹ ARC Centre for Antimatter-Matter Studies, School of Chemical and Physical Sciences, Flinders University, GPO Box 2100, 5001 Adelaide SA, Australia
² Department of Physics, Sophia University, Chiyoda-ku, 102-8554 Tokyo, Japan
³ Institute of Mathematical Sciences, University of Malaya, 50603 Kuala Lumpur, Malaysia

^a e-mail: laurence.campbell@flinders.edu.au

Received: 28 October 2011
Received in final form: 19 December 2011
Published online: 31 January 2012

Abstract

Recent measurements of integral cross sections for electron impact excitation of the Schumann-Runge continuum, longest band and second band of molecular oxygen are applied to calculations of emissions from the atmosphere of Europa. Molecules excited to these bands predissociate, producing O(¹D) (excited oxygen) atoms which subsequently decay to produce 630.0-nm radiation. Radiation of this wavelength is also produced by direct excitation of O atoms and by the recombination of O₂⁺ with electrons, but these two processes also produce O(¹S) atoms which then emit at 557.7 nm. It is shown by modeling that the ratio of 630.0-nm to 557.7-nm is sensitive to the relative importance of the three processes, suggesting that the ratio would be a useful remote sensing probe in the atmosphere of Europa. In particular, the excitation of the Schumann-Runge continuum, longest band and second band is produced by magnetospheric electrons while the recombination is produced by secondary electrons produced in the atmosphere. This difference raises the possibility of determination of the secondary electron spectrum by measurement of light emissions.