Anharmonicity effects in the vibrational CD spectra of propylene oxide

This study reports the first vibrational circular dichroism (VCD) spectra of propylene oxide isolated in an argon matrix. The narrow bandwidth achieved, in addition to the rich VCD features, allows a thorough analysis of the spectra and detailed comparison with the calculated harmonic and anharmonic IR and VCD spectra. Several bands in the fingerprint region are identified as nonfundamental modes based on the harmonic calculation, and three of them feature significant VCD intensity. Anharmonic VCD intensity calculations were carried out using a newly developed methodology based on the second-order level of vibrational perturbation theory. All new bands observed can be undoubtedly assigned to combination or overtone modes except the band at 1486.4 cm -1, which is tentatively identified to contain contributions from an overtone and a combination mode. The study also reveals that the current theoretical approach for anharmonic contributions to VCD spectra needs to be further improved when there is an accidental resonance involved.