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

Area of Science:

• Quantum chemistry
• Atomic and molecular physics
• Condensed matter physics

Background:

• Interchange tunneling splitting is a quantum mechanical phenomenon crucial for understanding molecular dynamics in clusters.
• Helium clusters provide a unique environment for studying fundamental quantum effects due to their weakly interacting nature.

Purpose of the Study:

• To investigate the effect of helium atom number (n=1-10) on the interchange tunneling splitting of (4)He(n)(HF)(2) clusters.
• To compare calculated results with experimental measurements of hydrogen fluoride dimer tunneling in helium nanodroplets.

Main Methods:

• Diffusion quantum Monte Carlo (DQMC) calculations were employed to determine the tunneling splitting.
• The study focused on the (4)He(n)(HF)(2) cluster system with varying numbers of helium atoms.

Main Results:

• Tunneling splitting decreases rapidly for n=1-4 helium atoms and much more slowly for n>4.
• Calculated reduction in tunneling splitting for (4)He(n)(HF)(2) accounts for 74% of the experimentally observed reduction in large helium nanodroplets.
• The first four helium atoms efficiently quench tunneling by occupying the equatorial ring around the transition state.

Conclusions:

• The initial solvation of helium atoms around the hydrogen fluoride dimer plays a critical role in suppressing interchange tunneling.
• The findings provide insights into the quantum behavior of small molecules in superfluid helium environments.
• DQMC calculations accurately reproduce experimental trends, validating the theoretical approach for studying such systems.