Magnetic resonance of a single molecular spin

Magnetic-resonance spectroscopy on single molecules represents the ultimate limit in sensitivity of electron spin resonance: the detection of a single molecular spin. This is achieved by combining single molecule spectroscopy and optically detected magnetic resonance. Experimental results on pentacene in p-terphenyl both in zero-field and in the presence of a weak magnetic field demonstrate that magnetic-resonance spectroscopy on single molecules adds on to the specificity of single-molecule spectroscopy. It proved possible to identify single molecules which contain C-13 nuclei in natural abundance and to observe the splitting of the electron spin resonance line resulting from the hyperfine intercation of a single molecular spin with a single C-13 nuclear spin. From the Zeeman effect the orientation of the symmetry axes of individual molecules with respect to the direction of the external magnetic field is obtained. This allows to compare the orientation of individual molecules with their substitutional-site specific transition frequencies depending on the quality of the host crystal. (C) 1999 Elsevier Science B.V. All rights reserved.