A diabatic state model for double proton transfer in hydrogen bonded complexes

TL;DR

This paper introduces a simple diabatic state model for double proton transfer in hydrogen bonded complexes, highlighting how key parameters influence the potential energy surface and transfer mechanism.

Contribution

It develops a minimal model using four diabatic states to analyze double proton transfer, revealing different transfer mechanisms based on system parameters.

Findings

Model describes four types of potential energy surfaces.

Transition from concerted to sequential transfer occurs as parameters change.

In the limit, the model simplifies to two decoupled hydrogen bonds.

Abstract

Four diabatic states are used to construct a simple model for double proton transfer in hydrogen bonded complexes. Key parameters in the model are the proton donor-acceptor separation R and the ratio, D_1/D_2, between the proton affinity of a donor with one and two protons. Depending on the values of these two parameters the model describes four qualitatively different ground state potential energy surfaces, having zero, one, two, or four saddle points. In the limit D_2=D_1 the model reduces to two decoupled hydrogen bonds. As R decreases a transition can occur from a concerted to a sequential mechanism for double proton transfer.