Vibrational Mode-Dependent Circular Dichroism of Jet-Cooled Styrene Oxide

Vibrational mode-dependent circular dichroism (CD) effects in vibrational CD spectra are often used to determine the handedness of molecules with multiple chiral centers. Here, we investigate vibrational mode-dependent CD effects in the electronic CD spectra of jet-cooled (<i>R</i>)-(+)- and (<i>S</i>)-(-)-styrene oxide obtained by using resonant two-photon ionization CD (R2PICD) spectroscopy. Although most fundamental vibronic bands demonstrated CD signatures consistent with that of the origin band, the overtone and combination bands exhibited opposite CD signatures. Theoretical calculations suggest that CD in fundamental bands are primarily governed by Franck-Condon contributions, whereas Herzberg-Teller contributions, which reflect the influences of vibrational modes on CD values, become more significant in overtone and combination bands. These results underscore the potential of mode-dependent vibronic CD signals in R2PICD spectra for determining the absolute configurations of molecules with multiple chiral centers.