Quantum Dynamics of H2 Trapped within Organic Clathrate Cages

Abstract

The rotational and translational dynamics of molecular hydrogen trapped within β-hydroquinone clathrate (H2@β-HQ)—a practical example of a quantum particle trapped within an anisotropic confining potential—were investigated using inelastic neutron scattering and Raman spectroscopy. High-resolution vibrational spectra, including those collected from the VISION spectrometer at Oak Ridge National Laboratory, indicate relatively strong attractive interaction between guest and host with a strikingly large splitting of rotational energy levels compared with similar guest-host systems. Unlike related molecular systems in which confined H2 exhibits nearly free rotation, the behavior of H2@β-HQ is explained using a two-dimensional (2D) hindered rotor model with barrier height more than 2 times the rotational constant (−16.2  meV).