Eur. Phys. J. D (2012) 66: 134
https://doi.org/10.1140/epjd/e2012-20657-8

Regular Article

Slow metastable H(2²S_1/2) from dissociation of cold H₂ induced by electrons

¹ Instituto de Física, Universidade Federal da Bahia, 40210-340 Salvador, BA, Brazil
² Laboratoire Aimé Cotton CNRS, Université Paris Sud 11, 91405 Orsay Cedex, France
³ Instituto de Física, UFRJ, Cx. Postal 68528, 21941-972 Rio de Janeiro, RJ, Brazil
⁴ Laboratoire Collisions Agrégats Réactivité, IRSAMC, Université Paul Sabatier, 31062 Toulouse Cedex 09, France
⁵ Departamento de Física, UFJF, MG, 36036-330 Juíz de Fora, Brazil

^a e-mail: aline.medina@ufba.br

Received: 11 November 2011
Received in final form: 13 February 2012
Published online: 23 May 2012

Abstract

We have produced slow metastable H(2²S_1/2) coming from the dissociation of cold H₂ induced by electron collisions. The experiment consisted of a supersonic jet of H₂ crossing electrons produced by a high intensity pulsed electron gun. The neutral fragments were detected through electric field induced Lyman-α radiation and their velocities were measured by time-of-flight (TOF) technique. The main characteristics of our experiment are the low molecular temperature, the long flight path and the small well defined collision and electric field regions. They give rise to precise velocity measurements and, consequently, to good spectra resolution. We have performed a careful analysis of the electron-molecule collision kinematical effects in order to identify which vibrational levels can be involved in the transition. Our results also explain the origin of the TOF peak widths. Relative probabilities to produce these levels have been deduced.