Accessing different binding sites of a multifunctional molecule: IR spectroscopy of propargyl alcoholwater complexes in helium droplets.

We report high-resolution infrared spectroscopic studies on complexes of propargyl alcohol with water (D2O) molecules, formed in superfluid helium droplets. The spectra were recorded in the frequency ranges of 2605-2700 cm-1 and 2730-2820 cm-1, covering the symmetric and antisymmetric stretching vibrations of the bound D2O. Mass-selective infrared spectroscopic measurements, a variation of the band intensities with dopant partial pressures (pickup curves) and ab initio calculations, performed at the MP2/6-311++G(d,p) level of theory, reveal the formation of two local minimum structures for the 1 : 1 PAD2O cluster. These structures are bound via O-HO (with water as the H-bond donor) and -C[triple bond, length as m-dash]C-HO (with propargyl alcohol as the H-bond donor) interactions and are less stable by 4.9 kJ mol-1 and 12.7 kJ mol-1, respectively, as compared to the global minimum structure for the complex.