The entrance channel complex in the exothermic OH + CH → HO + CH reaction has been isolated in helium nanodroplets following the sequential pick-up of the hydroxyl radical and methane. The a-type OH stretching band was probed with infrared depletion spectroscopy, revealing a spectrum qualitatively similar to that previously reported in the gas phase, but with additional substructure that is due to the different internal rotation states of methane (j = 0, 1, or 2) in the complex. We fit the spectra by assuming the rotational constants of the complex are the same for all internal rotation states; however, subband origins are found to decrease with increasing j. Measurements of deuterated complexes have also been made (OD-CH, OH-CD, and OD-CD), the relative linewidths of which provide information about the flow of vibrational energy in the complexes; vibrational lifetime broadening is prominent for OH-CH and OD-CD, for which the excited OX stretching state has a nearby CY stretching fundamental (X, Y = H or D).
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