MAGNETIC VIBRATIONAL CIRCULAR DICHROISM: EXPERIMENTAL STUDIES OF THE FARADAY

EFFECT IN MOLECULAR VIBRATIONS

Devine, Timothy Raymond

Abstract

A new magneto-optic, infrared, spectroscopic technique, magnetic vibrational circular dichroism (MVCD), is discussed. Theories of the origin of MVCD are reviewed and the experimental method is detailed. Experimental results are given for three systems of molecules in dilute solution.

MVCD results are detailed for four methyl halides, three haloforms, ammonia, methanol, and methanethiol in the C-H stretching and deformation regions. These are dominated by monosignate, positive and negative, MVCD B terms.

A series of aromatic molecules, including benzene, 1,3,5-trisubstituted benzenes, triphenylene, B-trichloroborazine, symtriazine, and several lower symmetry substituted benzenes and heterocycles are investigated in the ring stretching and C-H streching regions. The ring modes are dominated by A-term signals, positive and negative. Overtones of the fundamental ring stretches are found to have oppositely signed A terms from the fundamental.

MVCD results for three metal hexacarbonyls, (M(CO)₆, M = Cr, Mo, W) are given for the v₆(t_1u) C=O stretching mode. These spectra are dominated by large positive A terms. Results of combination bands at ~ 4000 cm^-1 are also presented. Finally, iron pentacarbonyl in the C=O stretching region and ferrocene in the C-H stretching region are found to give B-term MVCD.

The results are compared to predictions of the fixed partial charge and vibronic coupling models of MVCD. Strong correlations are found between methyl halide, haloform, and benzene-family molecules' MVCD in certain transitions and excited electronic state data.