| Abstract
| - UV absorption, magnetic circular (MCD), and linear (LD) dichroism of an n-tetrasilane configurationallyconstrained to the ortho conformation (calculated SiSiSiSi dihedral angle ω ≃ 95 °) are reported, and theresults are compared with the theoretical expectation of four low-energy transitions. Two strong UV absorptionmaxima with similar intensity and positive MCD B terms are assigned to states of B symmetry. A thirdcalculated transition to an 2A state was clearly detected in the LD spectrum, but a calculated weak transitionto a 31A state at a higher energy was not observed. The results support a previous rationalization of theconformational properties of the n-tetrasilane chromophore, according to which one of two low-energytransitions into B-symmetry states is of σσ* and the other of σπ* type in the planar cis and anti limits, andthey undergo a strongly avoided crossing as ω changes from 0° to 180°, keeping their energies nearly constantbut interchanging their oscillator strengths.
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