Electronic spectra of mono-substituted chromates

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Abstract
The electronic spectra of monosubstituted chromate ion derivatives, CrO3X-, where X-=F-, Cl-, Br- and IO3 -, have been measured at liquid helium temperature, employing a variety of sample forms. The observed electronic transitions correlate simply and directly with those of CrO4 2-, the lowest-lying transitions being only very weakly perturbed. Of particular interest is that the lowest excited state 1 Ea retains the peculiarities of the 1 T 1 parent state of CrO4 2-. The sharp line spectrum observed in Cr2O7 2- between 18 000 and 19 000 cm-1 is identified as 1 Ea (1 T 1 in T d) ←1 A 1 in a single O3CrO= chromophore. It is suggested that the observed features of the low-lying absorption bands can be explained by assuming that two spin-triplet states [3 E, 3 A 2] are located a few hundred wave numbers above the sharp 0-0 line of 1 Ea ←1 A 1.