CALCULATION OF NONADIABATIC MATRIX ELEMENTS CONSIDERING THE ANHARMONICITY EFFECTS OF MOLECULAR VIBRATIONS

The contribution of anharmonicity to the accepting and promoting modes in the tetraoxa[8]circulene molecule has been estimated. The estimates were made for the characteristic modes corresponding to the stretching vibrations of the X-H bonds, deformation vibrations, and stretching vibrations of the C-C bond. It was determined that the contribution of anharmonicity corrections is most pronounced for the promoting modes. Tetraoxa[8]circulene has only 2 accepting modes and 8 promoting modes. For these modes, the contribution of the anharmonicity from the partial derivatives of the potential energy with respect to the normal coordinates is insignificant, allowing for the use of the approximation of non-interacting modes when calculating the internal conversion rate constant. Expressions for calculating the internal conversion rate constant have been derived within the framework of first-order perturbation theory, taking into account the contribution of anharmonicity.