The GeOH+–HGeO+ system: A detailed quantum mechanical study

Abstract

The ground state potential energy hypersurface of the GeOH+–HGeO+ system has been investigated employing ab initio electronic structure theory. First, geometries of two equilibrium and isomerization (1,2 hydrogen shift) reaction transition state were determined at the self-consistent-field (SCF), configuration interaction with single and double excitations (CISD), coupled cluster with single and double excitations (CCSD), and CCSD with perturbative triple excitations [CCSD(T)] levels of theory using four basis sets. A qualitatively incorrect geometry is predicted for GeOH+ unless f functions are included in the basis set. Second, physical properties including dipole moments, harmonic vibrational frequencies, and infrared (IR) intensities of three stationary points were evaluated at the optimized geometries. The effects of electron 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 triple zeta plus double polarization with diffuse and higher angular momentum 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 for zero-point vibrational energies (ZPVEs), this energy difference becomes 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 (with 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 HGeO+ ion may be suitable for a microwave spectroscopic investigation. On the other hand, the GeOH+ ion may be suitable for an IR spectroscopic study due to the strong IR intensities of the three vibrational modes. The geometrical and energetic features are compared with those of the valence isoelectronic HCO+–COH+ and SiOH+–HSiO+ systems.