A molecular level study of the aqueous microsolvation of acetylene

We present an analysis of the structural, energetic and spectral features associated with the different hydrogen bonded networks found in the first few acetylene–water clusters AWn (n=1–4) from first principles calculations. Contrary to the predictions of an empirical interaction potential, acetylene is incorporated into a hydrogen bonded ring when it clusters with two or three water molecules. This structural pattern changes for n=4 with the formation of a water tetramer interacting with acetylene. This structural transition from n=3 to 4 is spectroscopically manifested by a qualitative change in the appearance of the infrared spectra of the corresponding global minima.