Auger Spectroscopy Techniques in Molecular Systems

Auger spectroscopy exploits the relaxation of a core‐ionised atom in a molecule, monitoring the energy of emitted electrons as one electron fills the vacancy and a second is ejected. This process provides element‐specific electronic fingerprints that are highly sensitive to local chemical environment, bonding, and charge distribution. In molecular systems, Auger techniques have evolved from conventional fixed‐energy measurements to advanced coincidence and time‐resolved schemes. Coincidence methods, such as Auger–photoelectron coincidence spectroscopy, enable direct correlation of core‐level ionisation with subsequent decay channels, isolating site‐selective interactions. The advent of ultrafast X-ray free‐electron lasers has further extended capabilities by inducing and probing multi‐core excitations and transient hollow or double‐core‐hole states on femtosecond timescales. The resulting spectra yield insights into electronic relaxation pathways, interatomic charge transfer and non‐linear ionisation dynamics. Applications range from mapping adsorbate–surface bonds in heterogeneous catalysis to monitoring ultrafast chemical reactions and assessing radiation damage in biological molecules. Ongoing technical refinements continue to enhance energy resolution, temporal precision and orbital specificity, underpinning the global significance of Auger spectroscopy for molecular science and materials research.

Research from Nature Portfolio

Recent studies have revealed the creation and decay of resonant double‐core excitations in diatomic molecules using intense few‐femtosecond X-ray pulses. In these experiments, two core electrons from distinct atomic sites are promoted simultaneously, and the ensuing decay channels are mapped via characteristic Auger signatures. The observations agree closely with high‐level theoretical models, demonstrating state‐ and site‐selective control of core excitations and suggesting routes for chemical analysis and ultrafast reaction monitoring. Another investigation quantified the prevalence of triple ionisation resulting from double Auger decay across a range of light‐element molecules. It was found that up to one-fifth of all core holes lead to emission of three electrons, with the degree of triple ionisation correlating linearly with the count of valence electrons in the local environment. These findings refine predictive models of molecular charge dynamics and have implications for radiation‐chemistry and imaging techniques. A third report characterised double K-hole pre-edge states in small polyatomic molecules, uncovering systematic distinctions between direct and conjugate shake-up processes. Spectral features associated with these pre-edge transitions shed light on orbital relaxation and electron correlation effects near double inner‐shell vacancies.

Research from all publishers

A detailed study of nitrous oxide multilayers adsorbed on nickel surfaces employed Auger–photoelectron coincidence spectroscopy to disentangle molecule–substrate interactions with orbital specificity. The nitrogen Auger spectra revealed donation–back‐donation bonding consistent with a Blyholder model, while oxygen signals remained unaffected by film thickness. Ab initio and molecular dynamics calculations supported assignment of spectral features to distinct nitrogen sites, demonstrating the power of coincidence methods to probe heterogeneous catalysis at the molecular level. Investigations of iodine‐containing molecules using hard X-ray photoelectron spectroscopy extended measurements up to 35 keV, capturing deep inner‐shell photoelectrons and subsequent L-MM and M-NN Auger electrons. Analysis of core‐hole lifetimes and chemical shifts provided insight into charge redistribution following photoionisation and highlighted the need for relativistic corrections in heavy‐atom systems. An earlier seminal work introduced partial covariance mapping to visualise femtosecond dynamics of hollow‐atom formation under intense X-ray free‐electron laser irradiation. By correlating ion yields and emitted electrons, the study uncovered nonlinear sequences of photoionisation and Auger decay events, laying groundwork for time‐resolved Auger spectroscopy of complex molecular systems.

Auger Spectroscopy Techniques in Molecular Systems publication trend

The graph below shows the total number of articles in auger spectroscopy techniques in molecular systems across all publications each year (not limited to Nature Index journals).

Technical terms

Auger decay: Non-radiative relaxation in which an electron fills a core vacancy and a second electron is emitted.

Core hole: A vacancy created in an inner atomic shell following ionisation or excitation.

Auger–photoelectron coincidence spectroscopy (APECS): A technique correlating core-level photoelectrons with subsequent Auger electrons to achieve chemical and orbital specificity.

X-ray free-electron laser (XFEL): A source of ultrashort, intense X-ray pulses enabling time-resolved studies of electronic dynamics.

Double-core-hole state: A highly excited configuration with two vacancies in inner atomic shells, often produced via multi-photon or resonant excitation.

Shake-up process: A simultaneous excitation of a valence electron during core-ionisation, leading to additional spectral features.

References

1. A Blyholder mechanism in the chemisorption of N2O on Ni(111) – studied with Auger-photoelectron coincidence spectroscopy. Applied Surface Science (2024).
2. Observation of molecular resonant double-core excitation driven by intense X-ray pulses. Communications Physics (2024).
3. Abundance of molecular triple ionization by double Auger decay. Scientific Reports (2018).
4. Cationic double K-hole pre-edge states of CS2 and SF6. Scientific Reports (2017).
5. Hard x-ray photoelectron spectroscopy on heavy atoms and heavy-element containing molecules using synchrotron radiation up to 35 keV at SPring-8 undulator beamlines. New Journal of Physics (2019).
6. Dynamics of Hollow Atom Formation in Intense X-Ray Pulses Probed by Partial Covariance Mapping. Physical Review Letters (2013).