Rotational Tunneling and Neutron Spectroscopy: A Compilation.

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.

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

Publisher Summary This chapter focuses on hole burning spectroscopy and physics of proteins. This chapter deals with the general aspects of the technique and the physics involved. This chapter also highlights the specific contributions from hole burning experiments to the understanding of photosynthesis. This chapter also discusses on the power of the hole burning technique in investigating disorder phenomena in proteins. By comparing proteins with crystals and glasses, this chapter shall try to characterize the specific features of the protein state of matter. This chapter presents the conclusion that even if such pronounced optical changes as the shift of a peak on the order of the inhomogeneous width are induced; the associated average structural changes are just at the resolution limit of X-rays as obtained from an analysis of the associated Debye-Waller Factors.

[10] Hole burning spectroscopy and physics of proteins

By applying an external electric field, we have studied the dc Stark shifts at the two states of a low-temperature single-molecule optical switch. We observe a reversible change from a mainly quadratic field dependence to a linear field dependence. The data analysis provides the S1-S0 dipole moment and polarizability differences of both the original and photoproduct state. On the basis of these data, a detailed microscopic scenario for the underlying nonphotochemical hole burning mechanism is discussed.

Nonphotochemical Hole Burning Investigated at the Single-Molecule Level: Stark Effect Measurements on the Original and Photoproduct State

Spectral hole burning is used to measure spin‐conversion relaxation of methyl groups attached to a dye probe. The dye is dimethyl‐s‐tetrazine, the host is n‐octane, which is, at low temperatures, a Shpol’skii‐matrix. The temperature dependence of the spin‐conversion relaxation follows the same pattern for the protonated and the perdeuterated methyl‐rotor. However, the relaxation rates of the perdeuterated rotor are higher by almost two orders of magnitude. Partial deuteration destroys the rotor symmetry and leads to a breakdown of the correlation between nuclear spin and rotational wave function.

Spin‐conversion relaxation in dimethyl‐s‐tetrazine doped n‐octane: Deuteration and symmetry breaking

We report a novel approach to measure rotational tunneling in condensed phases. High-resolution optical spectroscopic methods are used to unravel the tunneling level structure and to measure the rate of the nuclear-spin conversion. The method is demonstrated in experiments on the rotational motion of methyl groups in a crystal of durene doped with di-methyl-s-tetrazine but it can readily be transposed to other tunneling systems.

Oppenländer A

Papers

Optical measurements of methyl-group tunneling and nuclear-spin conversion.