Photoelectron Spectroscopy of Organic Molecules

Photoelectron spectroscopy (PES) has emerged as a cornerstone technique for probing the electronic structure of organic molecules, offering direct measurement of binding energies and orbital character. By irradiating a sample with photons of known energy—ranging from ultraviolet to soft X-rays—and analysing the kinetic energy of the emitted electrons, researchers can map valence and core-level spectra with high precision. In organic chemistry, PES illuminates how conjugation, heteroatoms and substituents modulate frontier orbitals, revealing details of electron delocalisation, intramolecular charge transfer and the influence of local chemical environment.

Advances in light sources and electron analysers have broadened the scope of PES. Synchrotron radiation facilities now enable angle-resolved and time-resolved measurements, tracing ultrafast electron dynamics and core-hole lifetimes. Laboratory-based laser sources facilitate resonant multiphoton ionisation studies that capture shape resonances and transient excited states. Together, these developments underpin applications in organic electronics, photovoltaics, surface science and astrochemistry, where a precise understanding of molecular ionisation underpins design of functional materials and interpretation of extraterrestrial spectra.

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Photoelectron Spectroscopy of Organic Molecules publication trend

The graph below shows the total number of articles in photoelectron spectroscopy of organic molecules across all publications each year (not limited to Nature Index journals).

Technical terms

Photoelectron Spectroscopy: Experimental method to measure kinetic energies of electrons emitted by photon impact, yielding binding energies and orbital information.

Binding Energy: The energy required to remove an electron from a specific molecular orbital or atomic core level.

Rydberg State: An excited electronic state in which an electron occupies an orbital with high principal quantum number, converging to an ionic limit.

Vibrational Progression: A series of spectral features corresponding to different vibrational excitations accompanying an electronic transition.

Shape Resonance: A transient trapping of an outgoing photoelectron by a molecular potential barrier, manifesting as a resonance in the continuum.

References

1. The vacuum UV photoabsorption spectroscopy of the cis-1,2-dichloroethylene (1,2-ClHC=CHCl) in the 5-20 eV range. An experimental and theoretical investigation. AIP Advances (2019).
2. A generic π* shape resonance observed in energy-dependent photoelectron angular distributions from two-colour, resonant multiphoton ionization of difluorobenzene isomers. The Journal of Chemical Physics (2013).
3. The vacuum UV photoabsorption spectrum of the geminal dichloroethylene (1,1-C2H2Cl2) in the 5–20 eV range. A vibrational analysis of the valence and Rydberg states. Journal of Physics Communications (2017).