Computation of the Tunneling Time in Tautomerization Reactions Based on Proton Transfer Through Static and Dynamical Barriers

ABSTRACT In the last decade, the rapid evolution of ultrafast laser spectroscopy has provided new impetus to the branch of chemistry dealing with tunneling processes involving electrons and light atoms. The possibility of measuring the time required by a particle to cross a barrier opens new perspectives for understanding the kinetics and dynamics of tunneling processes. In this study, a model is developed to estimate the tunneling time in tautomerization reactions based on proton transfer through a classically forbidden barrier. The proposed approach uses the asymptotic values of the wavefunction to compute the dwell time, which is the average time spent by the proton inside the potential barrier. The theory is formulated for both static barriers, which are good approximations for isolated molecules, and dynamic barriers to account for the effects of the chemical bath. The model performance is evaluated by two numerical simulations, in which a proton is transferred via tunneling in a double‐well potential; the tunneling barrier is approximated by a static and dynamical rectangular potential. A possible extension of the theory to open systems is briefly discussed within the framework of the Caldeira–Leggett model.