Hydrogen-atom tunneling reactions with methyl formate in solid para-hydrogen: Infrared spectra of the methoxy carbonyl [•C(O)OCH3] and formyloxy methyl [HC(O)OCH2•] radicals

Karolina A Haupa; Aaron I Strom; David T Anderson; Yuan-Pern Lee

doi:10.1063/1.5133089

Hydrogen-atom tunneling reactions with methyl formate in solid para-hydrogen: Infrared spectra of the methoxy carbonyl [•C(O)OCH₃] and formyloxy methyl [HC(O)OCH₂•] radicals

J Chem Phys. 2019 Dec 21;151(23):234302. doi: 10.1063/1.5133089.

Authors

Karolina A Haupa¹, Aaron I Strom², David T Anderson², Yuan-Pern Lee¹

Affiliations

¹ Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan.
² Department of Chemistry, University of Wyoming, Laramie, Wyoming 82071-3838, USA.

PMID: 31864267
DOI: 10.1063/1.5133089

Abstract

We investigated the reaction of methyl formate, HC(O)OCH₃, with hydrogen atoms in solid para-hydrogen (p-H₂) at 1.74 and 3.3 K with infrared absorption spectroscopy. Hydrogen atoms were produced either upon direct photolysis of HC(O)OCH₃ at 193 nm or upon irradiation of Cl₂, codeposited with HC(O)OCH₃ in p-H₂, with light at 365 nm to produce Cl atoms that react with the p-H₂ host via the reaction Cl + H₂ (ν = 1) → HCl + H induced by subsequent IR irradiation of the p-H₂ matrix. We assigned lines at 1785.2, 1170.6, 1104.6, and 879.4/880.5 cm^-1 and five additional weak lines to the methoxy carbonyl radical, •C(O)OCH₃, and three weak lines at 1751.3, 1152.9, and 994.4/996.8 cm^-1 to the formyloxy methyl radical, HC(O)OCH₂•, according to the consideration of possible reactions, correlated variations in intensities after each experimental step, and comparison of observed vibrational wavenumbers and IR intensities with values predicted with the B3LYP/aug-cc-pVTZ method. Unlike most reported H-atom diffusion tunneling reactions, the reaction H + HC(O)OCH₃ in solid p-H₂ at 3.3 K was found to diminish rapidly after IR irradiation, but, similar to reactions of H + N₂O and H + HC(O)OH, this reaction was reinitiated when the matrix temperature was decreased from 4.0 K to 1.5 K. We confirmed that the method used to generate the mobile H atoms does not affect the subsequent chemistry. A possible reaction mechanism and the role of this reaction in dark interstellar clouds are discussed.