THE GEOH-HGEO+ SYSTEM - A DETAILED QUANTUM-MECHANICAL STUDY()

The ground state potential energy hypersurface of the GeOH+-HGeO+ syst em has been investigated employing ab initio electronic structure theo ry. First, geometries of two equilibrium and isomerization (1,2 hydrog en shift) reaction transition state were determined at the self-consis tent-held (SCF), configuration interaction with single and double exci tations (CISD), coupled cluster with single and double excitations (CC SD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using four basis sets. A qualitatively incorrect geometry is p redicted for GeOH+ unless f functions are included in the basis set. S econd, physical properties including dipole moments, harmonic vibratio nal frequencies, and infrared (IR) intensities of three stationary poi nts were evaluated at the optimized geometries. The effects of electro n correlation reduce the dipole moment of HGeO+ by 1.25 Debye. At the highest level of theory employed in this study, CCSD(T) using the trip le zeta plus double polarization with diffuse and higher angular momen tum functions [TZ2P(f,d)+diff] basis set, linear GeOH+ is predicted to be more stable than linear HGeO+ by 71.7 kcal/mol. After correction f or zero-point vibrational energies (ZPVEs), this energy difference bec omes 70.3 kcal/mol. With the same method the classical barrier height for the exothermic isomerization (1,2 hydrogen shift) reaction HGeO+-- >GeOH+ is determined to be 30.3 kcal/mol and the activation energy (wi th the ZPVE correction) is 28.0 kcal/mol. The predicted dipole moments of GeOH+ and HGeO+ are 0.61 and 4.64 Debye, respectively. Thus, the H GeO+ ion may be suitable for a microwave spectroscopic investigation. On the other hand, the GeOH+ ion may be suitable for an LR spectroscop ic study due to the strong IR intensities of the three vibrational mod es. The geometrical and energetic features are compared with those of the valence isoelectronic HCO+-COH+ and SiOH+-HSiO+ systems. (C) 1995 American Institute of Physics.