STRUCTURES OF RYDBERG TRANSITIONS IN THE ABSORPTION-SPECTRA OF METHYL-SUBSTITUTED DERIVATIVES OF BIS(ETA(6)-BENZENE) CHROMIUM

The effect of methylation of ligands in bis(eta(6)-benzene)chromium (1 ) on the structure of Rydberg transitions in absorption spectra has be en studied. A detailed analysis and interpretation of all Rydberg elem ents of the vapor-phase spectra of bis(eta(6)-toluene)chromium (2), bi s(eta(6)-o-xylene)chromium (3), bis(eta(6)-m-xylene)chromium (4), and bis(eta(6)-mesitylene)chromium (5) was carried out. The vapor-phase el ectronic absorption spectrum of bis(eta(6)-p-xylene)chromium (6) was m easured, and the assignment of the Rydberg bands was made for the firs t time. The first ionization potentials of complexes 2-5 were refined. The energy of detachment of the 3d(z2) electron and the parameters of the Rydberg excitations for molecule 6 were determined. The vibronic components of the 3d(z2)-->R4p(x,y) transition in the spectra of compl exes 2 and 6 were assigned. The differences in the Rydberg structure o f the spectra of compounds 2-6 were analyzed in terms of the selection rules for optical transitions in the corresponding symmetry groups. T he vapor-phase spectra correspond to conformers with the symmetry grou ps C-2 nu and C-2 for complexes 2-4, with the symmetry groups D-3h and D-3 for compound 5, and with the symmetry group D-2d for complex 6.