Hannover 2013 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 11: Infrared and Microwave Spectroscopy

MO 11.4: Vortrag

Dienstag, 19. März 2013, 11:45–12:00, F 107

Internal Rotation and Nuclear Quadrupole Splitting in p-halo-toluenes (chloro-,bromo-,iodo-) — •V. Alvin Shubert, David Schmitz, Thomas Betz, and Melanie Schnell — Center for Free-Electron Laser Science, Hamburg, and Max-Planck-Institut für Kernphysik, Heidelberg, Germany

The presence of internal rotors and quadrupolar nuclei within a molecule give rise to microwave spectra exhibiting complex splitting patterns. These patterns offer insights into the internal dynamics and the influence of different substituents on the chemical and physical properties of large molecules. For example, the effect that the electronegativity of the halogen atoms has on the magnitude of the methyl group internal rotation barrier and the coupling between internal rotation and a quadrupolar nucleus. Such molecules containing both moieties have been previously studied,¹ and in order to further elucidate the combined effect, a series of p-halotoluenes (chloro-, bromo-, and iodo) were studied. We report the rotational spectra of these molecules in the frequency range 2-8.5 GHz obtained via the broadband microwave technique. The halogen atoms yield nuclear hyperfine splittings and the hindered methyl rotor with a barrier height, V₆, gives rise to additional splittings in the spectra. We will discuss the effect of the halogen group on the internal rotation barrier, the coupling between the quadrupolar nuclei and internal rotation, and compare our results to ab initio calculations.

¹M. Schnell, J.-U. Grabow, Angew. Chem. Int. Ed. 45, 3465-3470 (2006).