Isomer-Selective Vibrational Spectroscopy of Jet-Cooled Phenol–Acetylene Aggregates

The structures of the phenol (Ph)-acetylene (A) clusters PhA1,2,3 and Ph2A1 are assigned on the basis of isomer and mass specific IR-UV double resonance spectroscopy and compared to the structure of the PhA cocrystal. The structures of the PhA1,2,3 clusters are dominated by phenol-acetylene π-hydrogen bonds whereas Ph2A1 binds via OH···OH···C≡C interaction with dominating Ph-Ph hydrogen bond like in the phenol dimer and acetylene attached to the free OH group of the proton acceptor phenol. The macroscopic crystal is a clathrate of phenol with acetylene with hydrogen bridges only between the phenol molecules and not between phenol and acetylene. (1) A possible aggregation pathway is proposed in which larger phenol clusters like Ph6 are cyclic with no free OH available anymore to which acetylene could attach as proton acceptor.