Infrared Multiphoton Dissociation of Pentafluoroethane: Two-Channel Dissociation Process and Secondary Photolysis of Radical Products

Article abstract of DOI:10.1021/j150662a022

The dissociation yield and branching ratio in CO2 laser-induced multiphoton dissociation (MPD) of C2HF5 were investigated.In order to distinguish the two primary dissociation pathways (C2HF5 -> C2F4 + HF, E_a=71.6 kcal/mol; C2HF5 -> CF3 + CHF2, E_a=93.5 kcal/mol), Br2 was employed as an excellent scavenger of radicals and C2F4.The scavenged products were CBrF3, CHBrF2, CBr2F2, and C2Br2F4.The yield of C2Br2F4 originating from HF elimination was much smaller than those of CBrF3 and CHBrF2 from C-C bond rupture.The pulse energy dependence of the product distribution demonstrates that the primarily produced radicals were further photolyzed within the laser pulse (CF3 + nhν -> CF2 + F, and CHF2 + n'hν -> CF2 + H) to yield CBr2F2.The secondary photolysis of the radicals was also confirmed by real-time monitoring of infrared emission from HF^* and DF^* generated in the MPD of C2DF5 in the presence of H2 as an F atom scavenger.In the MPD of neat C2HF5, the formation of C2F4 was unexpectedly enhanced with increasing pulse energy; this was explained by assuming that C2F4 was mainly formed via recombination of CF2 radicals originating from the secondary photolysis of primarily produced radicals.