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Article Dans Une Revue (Article De Synthèse) International Reviews in Physical Chemistry Année : 2014

Ortho–para-H 2 conversion processes in astrophysical media

Résumé

We report in this review recent fully quantum time-independent calculations of cross sections and rate constants for the gas phase ortho-to-para conversion of H2 by H and H+. Such processes are of crucial interest and importance in various astrophysical environments. The investigated temperature ranges were 10–1500 K for H + H2 and 10–100 K for H+ + H2. Calculations were based on highly accurate H3 and global potential energy surfaces. Comparisons with previous calculations and with available measurements are presented and discussed. It is shown that the existence of a long-lived intermediate complex in the (barrierless) H+ + H2 reaction give rise to a pronounced resonance structure and a statistical behaviour, in contrast to H + H2 which proceeds through a barrier of ~5000 K. In the cold interstellar medium (T ≤ 100 K), the ortho-to-para conversion is thus driven by proton exchange while above ~300 K, the contribution of hydrogen atoms become significant or even dominant. Astrophysical applications are briefly discussed by comparing, in particular, the relative role of the conversion processes in the gas phase (via H, H+, H2 and ) and on the surface of dust particles. Perspectives concerning future calculations at higher temperatures are outlined.
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hal-04159232 , version 1 (18-02-2024)

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François Lique, Pascal Honvault, Alexandre Faure. Ortho–para-H 2 conversion processes in astrophysical media. International Reviews in Physical Chemistry, 2014, 33 (1), pp.125-149. ⟨10.1080/0144235X.2014.897443⟩. ⟨hal-04159232⟩
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