HF dimer in small helium clusters: Interchange-tunneling dynamics in a quantum environment

The diffusion quantum Monte Carlo calculations of the interchange tunneling splitting of ⁴He_n(HF)₂ clusters, n = 1-10, were presented. It was found that the tunneling splitting decreases rapidly for n = 1-4 clusters, and slowly for n > 4 and this decrease represented 74% of the reduction in the tunneling splitting measured for HF dimer in nanodroplets of more than 2000 He atoms. The results showed that the first four He atoms quenched the interchange tunneling efficiently by virtue of occupying the equatorial ring which encircled the C_2h transition state of the tunneling pathway.