Multiconfiguration Molecular Mechanics Studies for the Potential Energy Surfaces of the Excited State Double Proton Transfer in the 1:1 7-Azaindole:H2OComplex

Abstract

The multiconfiguration molecular mechanics (MCMM) algorithm was used to generate potential and vibrationally adiabatic energy surfaces for excited-state tautomerization in the 1:1 7-azaindole:H2O complex. Electronic structures and energies for reactant, product, transition state were computed at the CIS/6-31G(d,p) level of theory. The potential and vibrationally adiabatic energies along the reaction coordinate were generated step by step by using 16 high-level Shepard points, which were computed at the CIS/6-31G(d,p) level. This study shows that the MCMM method was applied successfully to make quite reasonable potential and adiabatic energy curves for the excited-state double proton transfer reaction. No stable intermediates are present in the potential energy curve along the reaction coordinate of the excited-state double proton transfer in the 1:1 7-azaindole:H2O complex, indicating that these two protons are transferred concertedly. The change in the bond distances along the reaction coordinate shows that two protons move very asynchronously to make an H3O + -like moiety at the transition state.