title: Investigation of multiple electronic excited state relaxation pathways following 200 nm photolysis of gas-phase imidazole.
abstract: Imidazole acts as a subunit in the DNA base adenine and the amino acid histidine-both important biomolecules which display low fluorescence quantum yields following UV excitation. The low fluorescence quantum yields are attributed to competing non-radiative excited state relaxation pathways that operate on ultrafast timescales. Imidazole is investigated here as a model compound due to its accessibility to high level ab initio calculations and time-resolved gas-phase spectroscopic techniques. Recent non-adiabatic dynamics simulations have identified three non-radiative relaxation mechanisms which are active following 6.0-6.2 eV excitation. Presented herein is a comprehensive investigation of each mechanism using a combination of femtosecond time-resolved ion yield and total kinetic energy release spectroscopies to monitor the formation of associated photoproducts. Relaxation along the (1)πσ state constitutes the predominant deactivation pathway. Timescales for NH-dissociation are extracted and distinguished from alternative H-atom sources based on their kinetic energy distributions. Larger photoproducts are observed to a lesser extent and attributed to ring fragmentation following NH-puckering and CN-stretching relaxation paths.
authors.affiliation: Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602, USA.
authors.forename: Hui
authors.initials: H
authors.lastname: Yu
authors.forename: Nicholas L
authors.initials: NL
authors.lastname: Evans
authors.forename: Vasilios G
authors.initials: VG
authors.lastname: Stavros
authors.forename: Susanne
authors.initials: S
authors.lastname: Ullrich
mesh_terms: D003116:Color; D004583:Electrons; D005740:Gases / Q000737:chemistry*; D007093:Imidazoles / Q000737:chemistry*; D007700:Kinetics; D010782:Photolysis; D013057:Spectrum Analysis
chemical_list: D005740:Gases; D007093:Imidazoles; C029899:imidazole