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 (R)–(+)– and (S)–(−)–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.

中文翻译：

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射流冷却苯乙烯氧化物的振动模式依赖性圆二色性


振动 CD 光谱中的振动模式依赖性圆二色性 （CD） 效应通常用于确定具有多个手性中心的分子的旋向性。在这里，我们研究了通过使用谐振双光子电离 CD （R2PICD） 光谱获得的喷射冷却 （R）–（+）– 和 （S）–（−）–苯乙烯氧化物的电子 CD 光谱中的振动模式依赖性 CD 效应。尽管大多数基本振动带表现出与原始带一致的 CD 特征，但泛音和组合带表现出相反的 CD 特征。理论计算表明，基频带中的 CD 主要受 Franck-Condon 贡献的影响，而 Herzberg-Teller 贡献（反映振动模式对 CD 值的影响）在泛音和组合频带中变得更加重要。这些结果强调了 R2PICD 光谱中模式依赖性振动 CD 信号在确定具有多个手性中心的分子的绝对构型方面的潜力。