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Title: Bimolecular reaction of CH{sub 3} + CO in solid p-H{sub 2}: Infrared absorption of acetyl radical (CH{sub 3}CO) and CH{sub 3}-CO complex

We have recorded infrared spectra of acetyl radical (CH{sub 3}CO) and CH{sub 3}-CO complex in solid para-hydrogen (p-H{sub 2}). Upon irradiation at 248 nm of CH{sub 3}C(O)Cl/p-H{sub 2} matrices, CH{sub 3}CO was identified as the major product; characteristic intense IR absorption features at 2990.3 (ν{sub 9}), 2989.1 (ν{sub 1}), 2915.6 (ν{sub 2}), 1880.5 (ν{sub 3}), 1419.9 (ν{sub 10}), 1323.2 (ν{sub 5}), 836.6 (ν{sub 7}), and 468.1 (ν{sub 8}) cm{sup −1} were observed. When CD{sub 3}C(O)Cl was used, lines of CD{sub 3}CO at 2246.2 (ν{sub 9}), 2244.0 (ν{sub 1}), 1866.1 (ν{sub 3}), 1046.7 (ν{sub 5}), 1029.7 (ν{sub 4}), 1027.5 (ν{sub 10}), 889.1 (ν{sub 6}), and 723.8 (ν{sub 7}) cm{sup −1} appeared. Previous studies characterized only three vibrational modes of CH{sub 3}CO and one mode of CD{sub 3}CO in solid Ar. In contrast, upon photolysis of a CH{sub 3}I/CO/p-H{sub 2} matrix with light at 248 nm and subsequent annealing at 5.1 K before re-cooling to 3.2 K, the CH{sub 3}-CO complex was observed with characteristic IR features at 3165.7, 3164.5, 2150.1, 1397.6, 1396.4, and 613.0 cm{sup −1}. The assignments are based on photolytic behavior, observed deuterium isotopic shifts, and a comparison of observed vibrational wavenumbers and relative IR intensities with those predictedmore » with quantum-chemical calculations. This work clearly indicates that CH{sub 3}CO can be readily produced from photolysis of CH{sub 3}C(O)Cl because of the diminished cage effect in solid p-H{sub 2} but not from the reaction of CH{sub 3} + CO because of the reaction barrier. Even though CH{sub 3} has nascent kinetic energy greater than 87 kJ mol{sup −1} and internal energy ∼42 kJ mol{sup −1} upon photodissociation of CH{sub 3}I at 248 nm, its energy was rapidly quenched so that it was unable to overcome the barrier height of ∼27 kJ mol{sup −1} for the formation of CH{sub 3}CO from the CH{sub 3} + CO reaction; a barrierless channel for formation of a CH{sub 3}-CO complex was observed instead. This rapid quenching poses a limitation in production of free radicals via bimolecular reactions in p-H{sub 2}.« less
Authors:
 [1] ;  [1] ;  [2]
  1. Department of Applied Chemistry and Institute of Molecular Science, National Chiao Tung University, Hsinchu 30010, Taiwan (China)
  2. (China)
Publication Date:
OSTI Identifier:
22311287
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Chemical Physics; Journal Volume: 140; Journal Issue: 24; Other Information: (c) 2014 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL AND ANALYTICAL CHEMISTRY; ABSORPTION; ACETYL RADICALS; CARBON MONOXIDE; COMPLEXES; DEUTERIUM; DIFFUSION BARRIERS; DISSOCIATION; HYDROGEN; INFRARED SPECTRA; IRRADIATION; KINETIC ENERGY; METHYL IODIDE; PHOTOLYSIS; SOLIDS; SPECTRAL SHIFT