Vibrational relaxation of acetylene produced by the photolysis of vinyl bromide

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Abstract
Vibrational relaxation of the ν2 and 2ν2 CC stretch vibrational states in the ground electronic state of acetylene has been investigated using infrared kinetic spectroscopy. Excited vibrational states of acetylene are produced by 193 nm ArF excimer laser photolysis of vinyl bromide in a room-temperature helium buffer gas. Vibrational state populations are probed by direct absorption with the continuous single-frequency output of a color center laser operating in the 3 μm region. The vibrational transitions observed were the ν2+ν3−ν2 and the 2ν2+ν3−2ν2 combination bands. Rate constants for He vibrational relaxation are 1.5(3)×10−14 and 2.1(7)×10−14 cm3 molecule−1 s−1 for ν2 and 2ν2, respectively.