Quantitative Atom-Atom Potentials from Rotational Tunneling: Their Extraction and Their Use

Abstract

Key Words tunneling, force fields, quantum chemistry, neutron scattering s Abstract Rotational tunneling of small molecular groups has been the subject of considerable theoretical and experimental activity for several decades. Much of this activity has been driven by the promise of exploiting the extreme sensitivity of quantum tunneling to interatomic potentials, but until recently, there was no straightforward means by which quantitative information about these potentials could be extracted. This review explains how a quantitative method, suitable for general application, was developed. It then goes on to show how this has been used to understand tunneling systems for which no previous satisfactory explanation had been found. The application of the methodology, and its results, to other disciplines is discussed.

X-ray diffraction and inelastic neutron scattering study of 2,6-dimethylpyrazine (DMP) chloranilic acid (CLA) complex

“…A confirmation of the outlined interpretation requires a mathematical modeling of the lattice dynamics similar to Refs. [9,16] based on a precise knowl- The mode assignment is based on consistent interpretation of methyl rotational energies and earlier Gaussian calculations. edge of the low temperature crystal structure and appropriate force fields.…”

“…The tunnel splitting which is strictly correlated with the potential shape can be recorded by high resolution inelastic neutron spectroscopy (INS) at energy transfers of the order of leV. With the exponential dependence on the height of the rotational barrier rotational tunneling spectroscopy is the most sensitive methods to probe in our molecular alloy the presence and amount of charge transfer and, more general, to test or/and improve atom-atom potentials [15,16].…”

Rotational Tunneling States and the Non-Debye Specific Heat of Dipolar Glasses

“…In principle, the tunneling data can be used to get details of the hindering potential V(θ) experienced by NH + 4 ion. 22,34,35 We are, however, largely concerned with establishing a correlation between the tunneling spectra and non-Debye specific heat and will thus not get into the calculation of potentials etc.…”

Dynamics of Atoms and Molecules

“…When tunneling can be observed however, it gives a very precise measure of the potential-energy surface that controls the quantum motion as illustrated in the review article [48]. First, as the temperature increases, the coherence between the tunneling sites is usually lost rapidly and the motion becomes more classical-like and diffusive.…”