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. 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.