Study of the CH3⋯H2O radical complex stabilized in helium nanodroplets

Abstract

The weakly bound CH₃⋯H₂O radical complex has been investigated by infrared laser spectroscopy. The complex is stabilized in helium nanodroplets and prepared by sequential pick up of a methyl radical and water molecule. Partially rotationally resolved spectra corresponding to the v = 1 ← 0 excitation of the symmetric H₂O stretching vibration within the complex show a significant red shift (25.06 cm⁻¹) when compared with the symmetric stretch of H₂O monomer, in agreement with the hydrogen bonded like structure derived by theory. Additional broad features were observed in the region predicted by theory for the antisymmetric stretch supporting our assignment. The B rotational constant is found to be 3.03 times smaller than predicted by ab initio calculations, with the reduction being attributed to the effects of helium solvation. The permanent electric dipole moment of the complex is experimentally determined to be 2.1 ± 0.3 D using Stark spectroscopy. Ab initio calculations are also reported that provide support to the experimental results, as well as investigate the nature of large amplitude vibrational motion within the complex.