New and Renewable Energy Research Center, Ewha Womans University, Seoul 03760, South Korea.
Department of Chemistry and Nanoscience, Ewha Womans University, Seoul 03760, South Korea.
J Phys Chem A. 2021 Mar 25;125(11):2356-2363. doi: 10.1021/acs.jpca.1c01093. Epub 2021 Mar 16.
2-Cyclopenten-1-one (2CP), which is a cyclic enone, has been considered an important precursor because of its versatile functionality in the synthesis of natural products and materials for biofuels. Here, we report the adiabatic ionization energy (AIE) and cationic structure of 2CP in the ionic transition between the neutral S and the cationic D states probed by high-resolution vacuum ultraviolet mass-analyzed threshold ionization (VUV-MATI) spectroscopy. From the 0-0 band position in the VUV-MATI spectrum supported by the VUV-photoionization efficiency curve, the AIE of 2CP was determined to be 9.3477 ± 0.0004 eV (75,395 ± 3 cm), which is in good agreement with the reference value but much more accurate. The measured MATI spectrum combined with the Franck-Condon fitting at the B3LYP/cc-pVTZ level revealed that the cationic structure of 2CP is twisted with the C symmetry, whereas the neutral 2CP has the C symmetry. The results indicate that geometrical changes induced by ionization are mainly attributed to the electron removal from the highest occupied molecular orbital, which consists of nonbonding orbitals on the oxygen atom in the carbonyl group interacting with the σ orbitals in the molecular plane of 2CP. Consequently, lowering the C symmetry for cationic 2CP led to the promotions of the ring-bending and ring-twisting modes in the MATI spectrum, which correspond to the ring puckering and C═C twisting in the S state, respectively.
2-环戊烯-1-酮（2CP）是一种环状烯酮，由于其在天然产物合成和生物燃料材料中的多功能性而被认为是一种重要的前体。在这里，我们报告了通过高分辨率真空紫外光电离效率曲线支持的真空紫外质量分析阈值电离（VUV-MATI）光谱在中性 S 和阳离子 D 态之间离子跃迁中 2CP 的绝热电离能（AIE）和阳离子结构。从 VUV-MATI 光谱的 0-0 带位置确定 2CP 的 AIE 为 9.3477 ± 0.0004 eV（75,395 ± 3 cm），与参考值吻合良好，但精度更高。测量的 MATI 光谱结合在 B3LYP/cc-pVTZ 水平下的 Franck-Condon 拟合表明，2CP 的阳离子结构是扭曲的，具有 C 对称性，而中性 2CP 具有 C 对称性。结果表明，电离引起的几何变化主要归因于从最高占据分子轨道中除去电子，该轨道由羰基中非键轨道与 2CP 分子平面中的σ轨道相互作用组成。因此，阳离子 2CP 的 C 对称性降低导致 MATI 光谱中环弯曲和环扭曲模式的提升，分别对应于 S 态中环的褶皱和 C═C 的扭曲。
