Accessing Different Binding Sites of a Multifunctional Molecule: IR Spectroscopy of Propargyl alcohol⋯Water 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 range 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 high-level ab initio calculations, performed at MP2/6-311++G(d,p) level of theory, reveal the formation of two local minimum structures for the 1:1 PA⋯D2O cluster. These structures are bound via O-H⋯O (with water as H-bond donor) and -C≡C-H⋯O (with propargyl alcohol as H-bond donor) interactions; and are less stable by 4.9 kJ/mol and 12.7 kJ/mol, respectively, as compared to the global minimum structure for the complex.