Spectra, Emission Yields, Cross Sections, and Kinetic Energy Distributions of Hydrogen Atoms From H₂ – Excitation by Electron Impact

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Electron-impact excitation of H 2 triplet states plays an important role in the heating of outer planet upper thermospheres. The state is the third ungerade triplet state, and the – emission is the largest cascade channel for the state. Accurate energies of the ( v, J ) levels are calculated from an ab initio potential energy curve. Radiative lifetimes of the ( v , J ) levels are obtained by an accurate evaluation of the – transition probabilities. The emission yields are determined from experimental lifetimes and calculated radiative lifetimes and are further verified by comparing experimental and synthetic – spectra at 20 eV impact energy. Spectral analysis revealed that multipolar components beyond the dipolar term are required to model the – excitation, and significant cascade excitation occurs at the ( v = 0,1) levels. Kinetic energy ( E k ) distributions of H atoms produced via predissociation of the state and the − − cascade dissociative emission are obtained. Predissociation of the state produces H atoms with an average E k of 2.3 ± 0.4 eV/atom, while the E k distribution of the − − channel is similar to that of the – − channel and produces H(1 s ) atoms with an average E k of 1.15 ± 0.05 eV/atom. On average, each H 2 excited to the state in an H 2 -dominated atmosphere deposits 3.3 ± 0.4 eV into the atmosphere, while each H 2 directly excited to the state gives 2.2–2.3 eV to the atmosphere. The spectral distribution of the calculated – <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999