Gibbard Jemma A, Clarke Connor J, Verlet Jan R R
Department of Chemistry, Durham University, Durham, DH1 3LE, UK.
Phys Chem Chem Phys. 2021 Sep 14;23(34):18425-18431. doi: 10.1039/d1cp03075b. Epub 2021 Aug 23.
Two-dimensional photoelectron spectroscopy using nanosecond and femtosecond lasers has been used to study the protopophyrin IX dianion at photon energies between 1.8-4.1 eV. The photoelectron spectra indicated the presence of two direct detachment channels, tunnelling through the repulsive Coulomb barrier (RCB) and thermionic emission from monoanions. A direct detachment feature suggested a near 0 eV electron affinity, which may be attributable to the repulsive through space interaction of the unshielded carboxylate groups. The minimum height of the repulsive Coulomb barrier (RCB) was found to be between 1.4-1.9 eV. Adiabatic tunnelling through the RCB was seen to occur on a timescale faster than rotational dephasing of the molecule. The observation of thermionic emission below the RCB in the nanosecond spectra originated from monoanions, which were produced via photon-cycling of the dianion.
使用纳秒和飞秒激光的二维光电子能谱已被用于研究光子能量在1.8 - 4.1电子伏特之间的原卟啉IX二价阴离子。光电子能谱表明存在两个直接脱离通道，即隧穿通过排斥性库仑势垒（RCB）和单阴离子的热电子发射。一个直接脱离特征表明电子亲和能接近0电子伏特，这可能归因于未屏蔽的羧基之间通过空间的排斥相互作用。发现排斥性库仑势垒（RCB）的最小高度在1.4 - 1.9电子伏特之间。通过RCB的绝热隧穿发生的时间尺度比分子的旋转退相快。在纳秒光谱中观察到RCB以下的热电子发射源于单阴离子，其通过二价阴离子的光子循环产生。
