Circular dichroism of an optically active benzene chromophore-1-methylindan

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Abstract
The gas phase circular dichroism and absorption spectra of a conformationally stable, optically active benzene chromophore, S‐(+)‐1‐methylindan, has been measured from 280 to 170 nm. The structure of the CD spectrum differs from that of the absorption in the B1u region and this observation is interpreted as evidence for the presence of a σ−π* or π−σ* E1g state in addition to the π−π* B1u state. Also, the CD spectrum near 190 nm requires the conclusion that an additional electronic state is located between the analogs of the B1u and E1u states. This state is assigned as E2g, in agreement with consistent theoretical predictions. The observed CD spectra can be accounted for in a consistent manner on the basis of a scheme which uses the results of parametrized calculations of coupled‐oscillator contributions and one‐electron term calculation results due to Caldwell and Kauzmann for the molecule studied.