AB-INITIO STUDIES ON HYDROGEN-TRANSFER TUNNELING FOR CL+HCL ABSTRACTION HYDROGEN REACTION

This article presents a treatment scheme of the tunneling of hydrogen between two molecular centers (Cl ... Cl). The purpose is to calculate the tunneling probabilities of hydrogen atom transfer from the initia l (the proceeding complex) to the final-state energy minima (the succe eding complex) in two anharmonic vibrational states (0 --> 0 and 1 --> 1) in terms of the time-dependent perturbation theory expression and to see whether spectroscopic signatures of tunneling persist in the fo rm of splittings of the vibrational modes. The analysis uses the reali stic potential energy function calculated at the HF/6-31 + G* self-co nsistent-field basis-set level for the interaction between transferred hydrogen and its molecular skeleton (Cl ... H ... Cl). This potential energy surface is calibrated by comparing its properties with those f rom sf-POLCI and the LEPS potential-energy surfaces. The anharmonic vi brational state is characterized by the corrected vibrational energy l evels and a set of linear combination coefficients obtained via pertur bation theory. The tunneling probabilities for two transitions (0 --> 0 and 1 --> 1) were calculated and compared with those from Gamow's eq uation. Applicability of the time-dependent perturbation theory expres sion and Gamow's equation to the [Cl-H ... Cl] system is discussed. Th e vibrational splitting energies are obtained, and a spectroscopic sig nature caused by tunneling is expected and should be observable. (C) 1 996 John Wiley & Sons, Inc.