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 pentace ne 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 poss ible to identify single molecules which contain C-13 nuclei in natural abun dance and to observe the splitting of the electron spin resonance line resu lting from the hyperfine intercation of a single molecular spin with a sing le C-13 nuclear spin. From the Zeeman effect the orientation of the symmetr y axes of individual molecules with respect to the direction of the externa l magnetic field is obtained. This allows to compare the orientation of ind ividual molecules with their substitutional-site specific transition freque ncies depending on the quality of the host crystal. (C) 1999 Elsevier Scien ce B.V. All rights reserved.