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Ionization and Photofragmentation of Isolated Metalloporphyrin Cations Investigated by VUV Action Spectroscopy

Schbert, K; Schwob, L; Dorner, S; Girod, M; MacAleese, L; Pieterse, C L; Schlatholter, T; Techert, S; Bari, S (2021) Ionization and Photofragmentation of Isolated Metalloporphyrin Cations Investigated by VUV Action Spectroscopy. Chemistry – A European Journal, 27 (48). pp. 12371-12379.

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Abstract

The isolated metalloporphyrin cations FePPIX+, CoPPIX+ and ZnPPIX+ have been studied in the gas phase by action spectroscopy in the vacuum-ultraviolet (VUV) range using electrospray ionization tandem mass spectrometry and synchrotron radiation. The ionization energy of each compound has been measured. Photoexcitation and photoionization lead to strikingly different fragmentation pathways. Evidence for non-statistical dissociation processes including water losses were identified. Fragment assignments have been supported by additional high-resolution collision-induced dissociation experiments on a hybrid quadrupole-orbital mass spectrometer.
We investigated the photoionization and fragmentation of isolated metal protoporphyrin IX cations (MPPIX+ with M=Fe, Co, Zn) by means of vacuum-ultraviolet (VUV) action spectroscopy in the energy range of 8.5–35 eV. Experiments were carried out in the gas phase by interfacing an electrospray ionization tandem mass spectrometer with a synchrotron beamline. The mass spectra and partial ion yields show that photoexcitation of the precursor ions predominantly leads to .CH2COOH radical side-chain losses of the macrocycle with additional methyl radical (.CH3) side-chain losses. Ionization, in contrast, leads to the formation of the intact ionized precursor and various doubly charged fragments which are mostly due to side-chain cleavages. Although statistical fragmentation dominates, we found evidence for non-statistical processes such as new fragments involving for example single and double H2O losses, indicating that different relaxation mechanisms are at play upon photoionization compared to photoexcitation. The measured ionization energies were 9.6±0.2 eV, 9.4±0.2 eV and 9.6±0.2 eV for FePPIX+, CoPPIX+ and ZnPPIX+, respectively.

Item Type: Article
Subjects: Nanoscience > Surface and Nanoanalysis
Divisions: Chemical & Biological Sciences
Identification number/DOI: 10.1002/chem.202101515
Last Modified: 04 May 2022 14:42
URI: http://eprintspublications.npl.co.uk/id/eprint/9435

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