Polarized single-crystal electronic spectra for tripotassium tetrasulfatodimolybdate-3. 5-water

Low-temperature polarized spectra for the band of K/sub 3/Mo/sub 2/(SO/sub 4/)/sub 4/ 3.5H/sub 2/O in the near-infrared region, between 5700 and 9000 cm/sup -1/, are reported. This band has rather remarkable vibrational structure which provides an exceptional picture of vibrations in the excited state. The data are consistent with an assignment of the band as the delta* reverse arrow delta, /sup 2/B/sub lu/ reverse arrow /sup 2/B/sub 2g/, dipole-allowed transition. The information, including hot bands developed in spectra above 80 K, indicates that the 0--0 lines of the two crystallographic sites are at 6311 and 6418 cm/sup -1/. However, there is no observed splitting of symmetry-related crystal (Davydov) states. Extended Franck--Condon progressions for each site based on a metal--metal stretching vibration of 350 cm/sup -1/ are observed. In addition, Franck--Condon terms of three other vibrations are seen. There are also weak featureless bands in the visible region at 16800 and 24000 cm/sup -1/.