School of Chemistry, Norwich Research Park, University of East Anglia, Norwich NR4 7TJ, United Kingdom.
Department of Chemistry, Temple University, 1901 N 13th Street, Philadelphia, Pennsylvania 19122, United States.
J Phys Chem Lett. 2021 Dec 16;12(49):11811-11816. doi: 10.1021/acs.jpclett.1c03532. Epub 2021 Dec 6.
Internal conversion between valence-localized and dipole-bound states is thought to be a ubiquitous process in polar molecular anions, yet there is limited direct evidence. Here, photodetachment action spectroscopy and time-resolved photoelectron imaging with a heteropolycyclic aromatic hydrocarbon (hetero-PAH) anion, deprotonated 1-pyrenol, is used to demonstrate a subpicosecond (τ = 160 ± 20 fs) valence to dipole-bound state internal conversion following excitation of the origin transition of the first valence-localized excited state. The internal conversion dynamics are evident in the photoelectron spectra and in the photoelectron angular distributions (β values) as the electronic character of the excited state population changes from valence to nonvalence. The dipole-bound state subsequently decays through mode-specific vibrational autodetachment with a lifetime τ = 11 ± 2 ps. These internal conversion and autodetachment dynamics are likely common in molecular anions but difficult to fingerprint due to the transient existence of the dipole-bound state. Potential implications of the present excited state dynamics for interstellar hetero-PAH anion formation are discussed.
价定域态和偶极束缚态之间的内转换被认为是极性分子阴离子中普遍存在的过程，但直接证据有限。在这里，使用杂多环芳烃（杂-PAH）阴离子、去质子化的 1-蒽醇的光电子离解作用光谱和时间分辨光电子成像来证明，在激发第一个价定域激发态的本征跃迁后，亚皮秒（τ=160±20 fs）价到偶极束缚态的内转换。内转换动力学在光电子能谱和光电子角分布（β 值）中显而易见，因为激发态的电子特性从价态变为非价态。随后，偶极束缚态通过特定模式的振动自动离解衰减，寿命τ=11±2 ps。这些内转换和自动离解动力学在分子阴离子中可能很常见，但由于偶极束缚态的瞬态存在，很难识别。本文讨论了目前激发态动力学对星际杂-PAH 阴离子形成的潜在影响。
