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Photoelectron spectroscopy of the protoporphyrin IX dianion

Gibbard, Jemma A. and Clarke, Connor J. and Verlet, Jan R. R. (2021) 'Photoelectron spectroscopy of the protoporphyrin IX dianion.', Physical Chemistry Chemical Physics, 23 (34).


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.

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Publisher statement:This article is Open Access. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence.
Date accepted:07 August 2021
Date deposited:16 November 2021
Date of first online publication:16 August 2021
Date first made open access:16 November 2021

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