Anomalous Doppler Broadening of Hydrogen Lines Caused by Exotermic Reactions

Large controversy is nowadays associated with possible explanations of the anomalous Doppler broadening of hydrogen Balmer lines observed in low-pressure plasma discharges. The interest was triggered by the observation of extraordinary wide wings on the spectrum of atomic hydrogen emitted lines. For full clearness of this point we present in this work a theoretical study in which the three-dimensional and one-dimensional velocity distributions of product species created by an exothermic reaction H$^{+}_{2}$ + H$_{2}$ --$>$ H$^{+}_{3}$ + H, with internal energy defect $\Delta $E, are determined using energy conservation requirement. It is shown that deviations relatively to Maxwell-Boltzmann distribution are significant as $\Delta $E increases and hence the profiles of H(n$\ge $3) emitting atoms created in the sequence of this reaction are not Gaussian. The determination of the species temperature from the full-width at half- maximum of hydrogen Balmer lines, as well as the fit of these lines by multimodel Gaussian functions are questioned.