ELECTRONIC EXCITED-STATES OF BIS(ETA(6)-ARENE) TUNGSTEN - AN INVESTIGATION BY ULTRAVIOLET PHOTOABSORPTION SPECTROSCOPY IN THE VAPOR AND SOLUTION PHASES

The electronic absorption spectra of (Bz)(2)W and (Tol)(2)W (Bz = eta( 6)-C6H6, Tol = eta(6)-C(6)H(5)Me) in the gas phase show comparatively narrow bands which are absent from the spectra in heptane solution. Th ese bands form two Rydberg series converging on the first ionization p otential. Series 1 is characterized by the quantum defect delta = 3.40 in both compounds. Series 2 shows delta = 3.15 in (Bz)(2)W and delta = 3.21 in (Tol)(2)W. Series 1 arises from the a(1g) --> Rnp(e(1u)) tra nsitions. Its first and second members are split into two components o n going from (Bz)(2)W to (Tol)(2)W. Series 2 corresponds to the a(1g) --> Rnp(a(2u)) excitations. In addition to these two series, the (Tol) (2)W vapour-phase spectrum contains the a(1g) --> R6s and a(1g) --> R6 d transitions which were interpreted on the basis of their term values . The first member of the Rnp(a(2u)) series is broadened beyond detect ion by admixture of valence-shell transitions. The interaction between electronic excited states results in deviation of the position of the second Rnp(e(1u)) series member from that predicted by the Rydberg fo rmula. The frequency of the lowest Rnp(e(1u)) transition deviates also from the theoretical value but this is mainly due to stronger penetra ting properties of the corresponding terminating orbital in comparison with the higher Rydberg orbitals. The vapour-phase spectra of (Bz)(2) W and (Tol)(2)W show no Rydberg features which might be considered a c onsequence of spin-orbit coupling caused by the presence of the heavy metal atom.