Eur. Phys. J. D 63, 421-429 (2011)
https://doi.org/10.1140/epjd/e2011-20028-1

Regular Article

Anomalous Doppler broadening caused by exothermic reactions: application to hydrogen Balmer lines

¹ Instituto de Plasmas e Fusão Nuclear-Laboratório Associado, Instituto Superior Técnico, Universidade Técnica de Lisboa, 1049-001 Lisboa, Portugal
² Laboratório Nacional de Ciência e Tecnologia do Bioetanol – CTBE, Caixa Postal 6170, CEP 13083-970 Campinas – SP, Brazil

^a e-mail: jorge.loureiro@ist.utl.pt

Received: 14 January 2011
Received in final form: 12 April 2011
Published online: 28 June 2011

Abstract

The three- and one-dimensional velocity distributions of a product species created by an exothermic reaction are calculated using the energy conservation, with the aim of evaluating the impact of such processes on the anomalous broadening of Doppler lines. The calculations are performed to the reaction H + H₂  →  H + H, in which according to Christoffersen (1964) an amount of 1.56 eV is transferred to the product species. It is shown that the deviations relatively to Maxwell-Boltzmann distributions are significant as the internal energy defect ΔE increases, even within energies lower than 1.56 eV, and hence the profiles of excited H^∗ atoms, associated with the emission of hydrogen Balmer lines, created in the sequence of H(n = 1) produced by the above reaction are not of Gaussian-type. The profiles are markedly flatter and squarer than Gaussian distributions. The validity of the species temperature determined from the full width at half maximum (FWHM) of the lines, as well as the fit of the lines by multimodal Gaussian functions, is then analyzed.