Isotope effect on the spectral shifts of C-13 substituted p-xylene

The carbon-13 isotope effect in the excitation spectra of p-xylene in the unseparated mixture as given by the natural abundance of C-13 was studied in a pulsed supersonic jet experiment with two-color resonance enhanced two-photon ionization, and analyzed in a reflectron time-of-flight mass spectrometer. The observed blue shifts in the spectra for the three isotopic configurations in the first electronic excited S-1 state relative to the p-xylene without a C-13 atom are 1.62, 3.64 and 5.12 cm(-1) respectively. From the shifts, the relative intensities of the peaks and theoretical calculations the position of the C-13 in the molecule could be identified and the spectra assigned. (C) 2000 Published by Elsevier Science B.V.