Rate constant for H-atom tunneling in the fluorene–acridine system based on DFT potential energy surface

Abstract

Abstract The dependence of the H-transfer rate constant of a solid phase tunneling reaction on temperature is analytically treated within the framework of a modified theory of radiationless transitions. Several intermolecular and soft intramolecular vibrations of reagents are taken into account, which result in oscillations of the potential barrier for the tunneling atom and thereby affect the value and temperature dependence of the rate constant. This treatment is used to interpret the experimental kinetic data of the fluorene–acridine reaction system involving hydrogen atom tunneling. It is shown that the correct estimations of the contributions related to both the reorganization of reagents and four types of promoting low-frequency vibrations (translational, librational and two intramolecular modes at 95 and 238 cm−1) are needed to reproduce the observed data. The reaction system parameters required for such analysis are extracted from the results of quantum-chemical calculations of two-dimensional potential energy surfaces carried out at the DFT-B3LYP/6-31G* level.