CONICET | Buscador de Institutos y Recursos Humanos

We present results of ring polymer molecular dynamics simulations that shed light on the effectsof nuclear quantum fluctuations on tunneling motions in cyclic [H$_2$O]$_3$ and [D$_2$O]$_3$,at the representative temperature of $T=75$ K. In particular, we focus attention on freeenergies associated with two key isomerization processes: The first one corresponds toflipping transitions of dangling OH bonds, between up and down positions with respectto the O-O-O plane of the cluster; the second involves theinterchange between connecting and dangling hydrogen bond character of the H-atoms ina tagged water molecule. Zero point energy and tunneling effects lead tosensible reductions of the free energy barriers.Due to the lighter nature of the H nuclei, these modifications are moremarked in [H$_2$O]$_3$ than in [D$_2$O]$_3$. Estimates of the characteristic timescalesdescribing the flipping transitions are consistent with those predicted based on standardtransition-state-approximation arguments.