Infrared spectra of propargyl alcohol dimers in helium nanodroplets

Propargyl alcohol (HC≡C-C(H2)-OH) and its clusters have been isolated in helium nanodroplets and probed using infrared spectroscopy. The global energy minimum of the dimer, in which a strong hydrogen bond forms between the two OH groups, does not yield the most intense spectral features. Instead, bands from a higher energy structure are prominent and derive from dimers held together primarily by a single and far weaker -C≡C-H⋯O-H hydrogen bond. This suggests that helium nanodroplet encapsulation kinetically traps the dimers in a local minimum on account of the rapid cooling and low temperature. This provides access to an unusual part of the potential energy surface of the dimer and, more generally, allows the probing of weak hydrogen bonding interactions.