Zeeman effect of single-molecule lines

The spectral line shifts induced by a magnetic field were measured for single terrylene molecules in the Shpol’skiĭ matrix n-hexadecane at liquid-helium temperatures. Quadratic red shifts with magnitudes between about 0 and −8 MHz/T2 were observed. The red shift is tentatively ascribed to a predominant contribution of van Vleck paramagnetism. The broad variation between the molecules is due to the random molecular orientations in different samples. The magnitude of the shift is much smaller than in porphyrins, since terrylene does not have two closely spaced excited states.