Simultaneous comparison of fluorescence spectrometry with multiphoton ionization spectrometry using a supersonic jet spectrometer

The ratio of the signal intensities obtained in multiphoton ionization spectrometry and fluorescence spectrometry is compared semi-quantitatively for several aromatic compounds. The ratios, normalized against N-ethylaniline, are 0.2-1 for aniline derivatives, however, the value for anthracene is 7 × 10^-6 in a one-colour ionization scheme and 7 × 10^-4 in a two-colour ionization scheme. The small value obtained for the] large' aromatic compound is ascribed to the high ionization potential relative to the two-photon energy for excitation and subsequent ionization; three photons are required in the one-colour scheme and an additional laser with sufficient energy must be aligned temporally and spatially for ionization in the two-colour scheme.