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Lack of resolution often limits the information that can be retrieved from electronic-excitation spectra of doped helium nanodroplets. The measurement of magnetic circular dichroism is a highly refined method to defeat spectral broadening by clever use of magnetic selection rules and associated sum rules [1]. The strong spectra observed in the presence of ground-state spin-degeneracy and excited-state spin orbit-coupling make the technique ideal to study alkali atoms and their high-spin oligomers (triplet dimers, quartet trimers) on the surface of He nanodroplets. We present a detailed analysis of these spectra, and show how they allow to explore different aspects such as optical pumping, excited-state dynamics, the Jahn-Teller effect, and the surface temperature of He nanodroplets. These measurements set the stage for optically-detected magnetic resonance, which we present separately. [1] Susan B. Piepho and Paul N. Schatz, Group theory in spectroscopy with applications to magnetic circular dichroism. Wiley 1983. |
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