Reactions between chlorine atom and acetylene in solid para-hydrogen: Infrared spectrum of the 1-chloroethyl radical

Abstract

We applied infrared matrix isolation spectroscopy to investigate the reactions between Cl atom and acetylene (C(2)H(2)) in a para-hydrogen (p-H(2)) matrix at 3.2 K; Cl was produced via photodissociation at 365 nm of matrix-isolated Cl(2) in situ. The 1-chloroethyl radical (center dot CHClCH(3)) and chloroethene (C(2)H(3)Cl) are identified as the main products of the reaction Cl + C(2)H(2) in solid p-H(2). IR absorption lines at 738.2, 1027.6, 1283.4, 1377.1, 1426.6, 1442.6, and 2861.2 cm (1) are assigned to the 1-chloroethyl radical. For the reaction of Cl + C(2)D(2), lines due to the center dot CDClCH(2)D radical and trans-CHDCDCl are observed; the former likely has a syn-conformation. These assignments are based on comparison of observed vibrational wavenumbers and (13)C- and D-isotopic shifts with those predicted with the B3LYP/aug-cc-pVDZ and MP2/aug-cc-pVDZ methods. Our observation indicates that the primary addition product of Cl + C(2)H(2), 2-chlorovinyl (center dot CHCHCl) reacts readily with a neighboring p-H(2) molecule to form center dot CHClCH(3) and C(2)H(3)Cl. Observation of center dot CDClCH(2)D and trans-CHDCDCl from Cl + C(2)D(2) further supports this conclusion. Although the reactivity of p-H(2) appears to be a disadvantage for making highly reactive free radicals in solid p-H(2), the formation of 1-chloroethyl radical indicates that this secondary reaction might be advantageous in producing radicals that are difficult to prepare from simple photolysis or bimolecular reactions in situ. (C) 2011 American Institute of Physics. [doi:10.1063/1.3653988]