Experimental and Theoretical Study of the O( 1 D) + HD Reaction

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This work addresses the kinetics and dynamics of the gas-phase reaction between O(1D) and HD molecules down to low temperature. Here, measurements were performed by using a supersonic flow (Laval nozzle) reactor coupled with pulsed laser photolysis for O(1D) production and pulsed-laser-induced fluorescence for O(1D) detection to obtain rate constants over the 50-300 K range. Additionally, temperature-dependent branching ratios (OD + H/OH + D) were obtained experimentally by comparison of the H/D atom atom yields with those of a reference reaction. In parallel, theoretical rate constants and branching ratios were calculated by using three different techniques; mean potential phase space theory (MPPST), the statistical quantum mechanical method (SQM), and ring polymer molecular dynamics (RPMD). Although the agreement between experimental and theoretical rate constants is reasonably good, with differences not exceeding 30% over the entire temperature range, the theoretical branching ratios derived by the MPPST and SQM methods are as much as 50% larger than the experimental ones. These results are presented in the context of earlier work, while the possible origins of the discrepancies between experiment and theory are discussed.
T.G.L. acknowledges support from MICINN with Grant FIS2017-83157-P. K.M.H. acknowledges support from the French programs “Physique et Chimie du Milieu Interstellaire” (PCMI) and “Programme National de Planetologie ́ ” (PNP) funded by the Centre National de la Recherche Scientifique (CNRS) and Centre National d’Etudes Spatiales (CNES). Y.V.S. acknowledges the support of the European Regional Development Fund and the Republic of Cyprus through the Research Promotion Foundation (Project: INFRASTRUCTURE/1216/00/0 and Cy-Tera NEA YΠOΔOMH/ΣTPATH/0308/31). Computer time was provided by the Pôle Modelisation HPC facilities of ́ the Institut des Sciences Moleculaires UMR 5255 CNRS ́ − Universitéde Bordeaux, cofunded by the Nouvelle Aquitaine region.