Direct Access to the Dipole-Forbidden nπ∗T1 State of p-Benzoquinone by Photodetachment Photoelectron Spectroscopy
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S. Siegert
Abstract
In this work we show that photodetachment photoelectron (PD-PE) spectroscopy on radical anions allows direct access to dark states, such as dipole-forbidden nπ∗ triplet and singlet states. p-benzoquinone (BQ) was chosen as model molecule because it is experimentally and theoretically well investigated and its lowest electronic states are electric dipole-forbidden nπ∗ triplet and singlet states. Because of the high density of electronic states we observe a dense structure with many transitions in our PD-PE spectrum. We identify the first peak at 2.3 eV above the S0 onset as the T1 state origin, in good agreement with previous data. We are not able to resolve the splitting between the states T1 (13B1g) and T2 (13Au) as well as the corresponding S1 (11Au) and S2 (11B1g) states, but perform a tentative assignment of the singlet-triplet splitting on the basis of literature data. The fact that the spectral features in our PD-PE spectrum cover a broad energy range is taken as a strong experimental evidence for the presence of the T3ππ∗ state, which has been predicted to lie in this energy range. Our investigations on BQ show that in principle, by starting spectroscopy in radical anions most of the selection rules, valid in neutral BQ molecules, can be circumvented and nπ∗ states, triplet states and other dipole-forbidden states become directly accessible with bright intensity. Much higher electron energy resolution is required to allow unambiguous assignments and make PD-PES of radical anions a valuable method for the spectroscopy dark states of neutral closed-shell molecules.
© by Oldenbourg Wissenschaftsverlag, München, Germany
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Artikel in diesem Heft
- Editorial
- Reactions between Cold CHx+ and Slow H and H2
- Reactions in Trifluoropropene and Trifluoropropyne Triggered by Low-Energy (0–12 eV) Electrons: From Single Bond Cleavages to Complex Unimolecular Decompositions
- Direct Access to the Dipole-Forbidden nπ∗T1 State of p-Benzoquinone by Photodetachment Photoelectron Spectroscopy
- Quantitative Study of 4He Real Gas Effects Using Supersonic Beams
- Large Amplitude Motions in Cyclopentene and 1-Butene: Quantum Chemical Insights into the Ground- and Excited State Potential Energy Surfaces
- Coherent Excitation Transfer Driven by Torsional Dynamics: a Model Hamiltonian for PPV Type Systems
- H-Bonding Cooperativity Effects in Amyloids: Quantum Mechanical and Molecular Mechanics Study
- Ultrafast Charge Separation at the CdSe Quantum Dot/Methylviologen Interface: Dependence on Electron Acceptor Concentration
- Circular Dichroism in Ion Yields in Multiphoton Ionization of (R)-Propylene Oxide Employing Femtosecond Laser Pulses
- The Interaction of the Dipeptide Carnosine With Alkali Metal Ions Studied by Ion Trap Mass Spectrometry
- Nonequilibrium NMR Methods for Monitoring Protein and RNA Folding
