Department of Chemistry and Institute for Molecular Science and Fusion Technology, Kangwon National University, Chuncheon 24341, Korea.
Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Korea.
J Chem Phys. 2018 Nov 7;149(17):174302. doi: 10.1063/1.5051682.
Isobutanal is an aliphatic aldehyde which has been extensively studied as an important intermediate in isomerization reactions as well as in astrochemically relevant models in the interstellar medium. Herein, we report on the conformer-specific photoionization and conformational stabilities of isobutanal utilizing one-photon mass-analyzed threshold ionization (MATI) spectroscopy with vacuum ultraviolet (VUV) pulses. The conformational population of isobutanal under different supersonic expansion conditions was explored to identify the conformers, from which their intrinsic photoionizations can be directly elucidated by measuring the VUV-MATI spectrum corresponding to each conformer. The observed MATI spectra could be analyzed through Franck-Condon simulations at the B3LYP/cc-pVTZ level for the isobutanal conformers, and , for which the adiabatic ionization energies were precisely determined to be 78 133 ± 3 cm (9.6873 ± 0.0004 eV) and 78 557 ± 3 cm (9.7398 ± 0.0004 eV), respectively. Notably, only the conformer undergoes a unique geometrical change upon ionization, resulting in the progression of the CHO torsional mode in the MATI spectra. Consequently, we determined the conformational stabilities of isobutanal by conformer-specific photoionization, given that the is more stable than the by 162 ± 50 cm in the neutral ground state, while the cationic is less stable than the cationic by 262 ± 50 cm.
异丁醛是一种脂肪族醛，它作为异构化反应以及星际介质中相关天体化学模型中的重要中间体而被广泛研究。在此，我们利用真空紫外（VUV）脉冲的单光子质量分析阈值电离（MATI）光谱法，报告了异丁醛的构象特异性光致电离和构象稳定性。通过探索异丁醛在不同超音速膨胀条件下的构象分布，我们确定了构象体，从中可以通过测量与每个构象体相对应的 VUV-MATI 谱，直接阐明其固有光致电离。观察到的 MATI 谱可以通过在 B3LYP/cc-pVTZ 水平上进行 Franck-Condon 模拟进行分析，对于异丁醛构象体 和 ，精确确定了它们的绝热电离能分别为 78133±3cm（9.6873±0.0004eV）和 78557±3cm（9.7398±0.0004eV）。值得注意的是，只有 构象体在光致电离时经历独特的几何变化，导致在 MATI 谱中 CHO 扭转模式的进展。因此，我们通过构象特异性光致电离确定了异丁醛的构象稳定性，因为在中性基态下， 比 稳定 162±50cm，而阳离子 比阳离子 不稳定 262±50cm。
