Accessing different binding sites of a multifunctional molecule: IR spectroscopy of propargyl alcohol⋯water complexes in helium droplets

Abstract

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 PA⋯D₂O cluster. These structures are bound via O–H⋯O (with water as the H-bond donor) and –CC–H⋯O (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.