Combined Effects from Solvation and Nuclear Quantum Fluctuations on Autoionization Mechanisms in Aqueous Clusters

RODRIGUEZ, J; LARIA, D; TURI L.

JOURNAL OF PHYSICAL CHEMISTRY B - (Print)

AMER CHEMICAL SOC

Lugar: WASHINGTON DC; Año: 2020 vol. 124 p. 2198 - 2208

1520-6106

Using Path Integral Molecular Dynamics simulations we examine isomerization paths involving collective proton transfers in [H2O]5 and [H2O]8 clusters at cryogenic conditions. We focused attention on combined effects derived from solvation and nuclear quantum fluctuations on the characteristics of free energy barriers and relative stabilities of reactants and products. In particular, we analyzed two different processes: the first one involves the exchange of donoracceptor hydrogen bond roles along cyclic moieties, whereas the second one corresponds to charge separation leading to stable [H3O]+[OH]- ion pairs. In the first case, the explicit incorporation of quantum tunneling introduces important modifications in the classical free energy profile. The resulting quantum profile presents two main contributions, one corresponding to compressions of O-O distances, and a second one ascribed to nuclear tunneling of the light protons. Solvation effects promote a moderate polarization of the cyclic structures and a partial loss of concertedness in the collective modes, most notably, at the onset of tunneling. Still, the latter effects are also sufficiently strong to promote the stabilization of ion pairs along the classical trajectories. Contrasting, the explicit incorporation of nuclear quantum fluctuations brings charge separated configurations marginally stable. As such, the latter states could be also regarded as short-lived intermediate states along the reactive exchange path.