Vibrationally mediated photodissociation of 1-butyne initially excited to the 3ν ₁ state

The vibrational spectrum of 1-butyne in the region of the second overtone of the C-H acetylenic stretch, 3ν ₁, was studied, for the first time, at room temperature by photoacoustic spectroscopy and under jet-cooled conditions by vibrationally mediated photodissociation. The latter resulted in a narrowed H action spectrum enabling observation of a splitting between 3ν ₁ and a close resonating state. The splitting and the simulation of the spectra contours allowed retrieving time scales for energy redistribution and interaction matrix elements. The low average translational energy extracted from the Doppler profile of the H atom argues against a direct dissociation process.