Theoretical study of multidimensional proton tunneling in the excited state of tropolone

摘要

Ab initio CIS/6-31G** and CIS/6-31++G** calculations have been carried out in the A state of tropolone for the stable and saddle point structures. The calculated energies and geometries have been compared with the previous results of Vener The energy barrier for the proton tunneling amounts to 12.0 kcal/mol from the CIS/6-31G** calculations, and 13.0 kcal/mol from the CIS/6-31++G** calculations. The normal mode frequencies have been computed including modes coupled to the proton tunneling mode. Two-dimensional and three-dimensional model potentials, formed from symmetric mode coupling potential and squeezed double well potential, have been fitted to the calculated energy barrier, geometries, and frequencies, and used to analyze proton dynamics. The calculated energy splittings for different vibrationally excited states have been compared with the available experimental data. The CIS/6-31++G** calculation gives good estimation of the tunneling energy splitting in the vibrationally ground state of tropolone. The model PES explain monotonic decrease in tunneling splittings with the excitation of the out-of-plane modes, however underestimate the actual splittings. The increase of the tunneling splitting with the excitation of the v(13) and v(14) modes is qualitatively correct. (C) 2000 American Institute of Physics. [S0021-9606(00)31113-8]. [References: 30]