Circular dichroism in the angle-resolved C 1s photoemission spectra of gas-phase carvone enantiomers.

The inner-shell C 1s photoionization of randomly oriented molecules of the chiral compound carvone has been investigated using circularly polarized synchrotron radiation up to 30 eV above threshold. Binding energies of the C_==O and C_H₂== carbon 1s orbitals were determined to be 292.8±0.2 and 289.8±0.2 eV, respectively. The remaining C_–H C 1s levels substantially overlap under an intense central peak centered at 290.5±0.2 eV. The angle-resolved photoemission from the carbonyl carbon C_==O core orbital in pure carvone enantiomers shows a pronounced circular dichroism of ∼6% at the magic angle of 54.7° to the light beam propagation direction. This corresponds to an expected 0°–180° forward-backward electron emission asymmetry of ∼10%. On changing between the R and S enantiomers of carvone the sense or sign of the asymmetry and associated dichroism effectively reverses. The observed circular dichroism, and its energy dependence, is well accounted for by calculations performed in the pure electric dipole approximation. [ABSTRACT FROM AUTHOR]