Microsolvation of the water cation in neon:: Infrared spectra and potential energy surface of the H2O+-Ne open-shell ionic complex

The intermolecular potential of the H2O+-Ne open-shell ionic dimer in its doublet electronic ground state has been investigated by infrared spectroscopy in the vicinity of the O-H stretch vibrations (nu (1) and nu (3)) and ab initio calculations at the unrestricted Moller-Plesset second-order (MP2) level with a basis set of aug-cc-pVTZ quality. The rovibrational structure of the photodissociation spectrum is consistent with a proton-bound planar H-O-H-Ne structure and a Ne-H separation of R-0=1.815(5) Angstrom. The complexation-induced redshifts are Delta nu (1)=-69 cm(-1) and Delta nu (3)=-6 cm(-1), respectively. Tunneling splittings observed in the perpendicular component of the nu (3) hybrid band of H2O+-Ne are attributed to hindered internal rotation between the two equivalent proton-bound equilibrium structures. The interpretation of the H2O+-Ne spectrum is supported by the spectrum of the monodeuterated species, for which both the proton-bound and the deuteron-bound isomers are observed (DOH+-Ne, HOD+-Ne). The equilibrium structure of the calculated potential energy surface of H2O+-Ne has a slightly translinear proton bond, which is characterized by a Ne-H separation of R-e=1.77 Angstrom, a bond angle of phi (e)=174 degrees, and dissociation energies of D-e=756 cm(-1) and D-0=476 cm(-1). According to the calculated potential, the exchange tunneling between the two equivalent minima occurs via the planar bridged transition state with C-2v symmetry and a barrier of 340 cm(-1). In general, the calculated properties of H2O+-Ne show good agreement with the experimental data. Initial steps in the microsolvation of the water cation in neon are discussed by comparing the calculated and experimental properties of H2O+-Ne-n (n=0-2) with neon matrix isolation data (n --> infinity). (C) 2001 American Institute of Physics.