Eur. Phys. J. D (2016) 70: 77
https://doi.org/10.1140/epjd/e2016-60473-6

Regular Article

Measuring electron-impact cross sections of water: elastic scattering and electronic excitation of the ã³B₁ and ùB₁ states

¹ Department of Physics, Sophia University, Chiyoda-ku, Tokyo 102-8554, Japan
² Laboratório de Colisões Atómicas e Moleculares, CEFITEC, Departamento de Física, Faculdade de Ciências e Tecnologia, Universidade NOVA de Lisboa, 2829-516 Caparica, Portugal

^a e-mail: masami-h@sophia.ac.jp

Received: 17 August 2015
Received in final form: 13 December 2015
Published online: 7 April 2016

Abstract

Here, we report elastic differential cross sections (DCSs) for electron scattering from water in the incident energy range of 2−100 eV. Furthermore, we present a complete study on the electronic excitation of the ã³B₁ and ùB₁ states at electron impact energies of 15, 20, and 30 eV and in the scattering angle range of 10° − 130°. Integral cross sections (ICSs) are determined from the DCSs. Measuring elastic DCSs in various experimental conditions confirmed the reproducibility of the data. The present results agree with the data previously obtained from a conventional collimating tube gas source. Ambiguities associated with the unfolding procedure of the electron energy loss (EEL) spectra for the electronic excitations have been reduced by comparison against the EEL spectrum at high electron impact energy and for small scattering angle. The reliability of the extracted DCSs is improved significantly for optically forbidden contributions from the overlap of the ã³B₁ and ùB₁ electronic states. The BEf-scaling model is also confirmed to produce the integral cross section for the optical allowed transition of the ùB₁ state in the intermediate electron energy region above 15 eV.