Determination of isotope shifts in 2,4-, 3,4- and 2,6-dichlorotoluene isomers in a supersonic beam

By using resonance-enhanced two-photon ionization in a supersonic beam, photoionization spectra of the m/z 160, 162 and 164 species of the 2,4-, 3,4- and 2,6-dichlorotoluene isomers at 0.8 K rotational temperature have been obtained in the 2800 Å spectral region. The ions have been analyzed according to their masses in a time-of-flight mass spectrometer. Isotope shifts of the order of tenths of cm⁻¹ have been determined for the first time for the studied molecules. The spectra obtained have been interpreted by considering the geometrical structure and symmetry of every isotopomer, and values for the rotational constants in the upper and lower states of the electronic transition have been obtained in agreement with the experimental results.