Infrared Multiphoton Photochemistry of Hexafluorobenzene Studied by Time-Resolved Visible Luminescence Spectroscopy

Article abstract of DOI:10.1021/j100245a015

C6F6 gas (0.15-3 torr) was irradiated with IR pulses at 1023 cm^-1, where C6F6 absorbs strongly, and the time evolution of the visible/near-UV luminescence spectrum was examined.IR pulse fluence ranged mostly from 100 to 900 J cm^-2, and square-pulse equivalent intensity from 2 to 18 GW cm^-2.By use of a plasma shutter to truncate IR pulses after ca. 60 ns, luminescence evolving during irradiation could be clearly distinguished from that emitted subsequently.Kinetic measurements at 360 nm showed that luminescence begins shortly (10-20 ns) after the start of the IR pulse.After pulse truncation, the initial decay of luminescence comprises two first-order lifetimes, τ_A ca. 15 ns and τ_B = 575+/-75 ns.Time-resolved spectroscopy shows that the 575-ns emission agrees closely with a well-characterized emission, previously assigned to C₃, seen in carbon furnaces and fuel-rich oxyacetylene flames.During the period 1.8-18.8 μs after the IR pulse, time-resolved spectra are dominated by broad-background emission, with sharp superposed intensity peaks assignable to C₂ Swan bands.The broad-background emission during this period agrees with blackbody radiation spectra for temperatures decreasing from 3640 to 3440 K.The luminescence yield for the background emission varies at the square of the initial C6F6 pressure.Final reaction products are mostly C2F4(g) and a black solid ("fluorocoal") of approximate composition (C2F)n.It is suggested that the final products indicate not how the parent molecules decompose but how the fragments formed from them reassemble afterward as the gas temperature returns to ambient.