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Circular dichroism in K-shell ionization of fixed in space CO and N2 molecules

We have measured the angular distributions of 1s-photoelectrons excited by circularly and linearly polarized light from fixed-in-space CO and N2 molecules, in the vicinity of their shape resonances. A strong circular dichroism, i.e. a strong dependence on the sense of rotation of the polarization vector of the photons, is found for both molecules.
State-of-the-art one-electron multiple scattering and partially-correlated random phase approximation calculations are in good agreement with many, but not all, aspects of the experimental data.

(a) and (b) - Angular distributions of C(1s) photo-electrons (10 eV kinetic energy, on shape resonance) emitted from a CO molecule by absorption of left and right circularly polarized photons. The sense of rotation of the polarization vector is indicated by the spiral, where the photon propagation vector lies along the + x-axis (i.e., into the page) in all cases. The molecule is aligned along the z-axis, with the carbon atom at negative z in panels (a) and (b).
Each vertex of the three-dimensional shape represents one data point. The data have not been smoothed, with the maximum corresponding to about 1000 counts.
(c) Analogous distribution of N(1s) photoelectrons (9 eV, on resonance) from N2.

(a-c) Angular distribution of C(1s) photo electrons emitted from a CO molecule by absorption of right circularly polarized photons where the propagation vector of the light is into the page. The molecule lies along the horizontal axis as indicated, and both electrons and molecules lie within 10 degrees of the plane of the page.
The electron energies are (a)1.6, (b) 10.0 and (c) 24.6 eV. Panels (d-f) show the corresponding circular dichroism. Electron angle 0 corresponds to the direction of the carbon. Full lines: Theoretical multiple scattering calculations for the two higher energies, convoluted with the experimental resolution.