Soft X-Ray Photoelectron Spectroscopy
Kai Siegbahn pioneered the electron spectroscopy for chemical analysis (ESCA) which has been developed into an indispensable analytical technique for surface science. The value of this powerful method, which was named later photoelectron spectroscopy (PES) was recognized in the 1981 Nobel Prize awarding in Physics. Nevertheless, the need for high vacuum prohibited PES of volatile liquids and only allowed for investigation of low-vapor-pressure molecules attached to a surface (or close to a surface) or liquid films of low volatility. With the invention of the liquid micro-jet technique by Faubel and co-workers, liquids became compatible under high-vacuum conditions, allowing PES investigations. Furthermore, PES from the solid/liquid interface under ambient conditions has been established at the Advanced Light Source of Berkeley lab by Bluhm et al. In 2006, Faubel and Winter reviewed the gas-to-liquid PES showing how one can extract valuable information about the MOs via the peak shifts (representing MO shifts), peak broadening (hybridization of MOs), and photoionization cross sections. PES can reveal charge- and site-specific electronic structural information of biomolecules in aqueous solution as well, e.g., for monitoring charge density modifications caused by proton attachment.
Illustration of a valence PES process
occuring in a transition metal ion.
Image taken from Lange et al.
- Aziz, Emad F., Niklas Ottosson, Manfred Faubel, Ingolf V. Hertel, and Bernd Winter. “Interaction Between Liquid Water and Hydroxide Revealed by Core-hole De-excitation.” Nature 455, no. 7209 (September 4, 2008): 89–91. doi:10.1038/nature07252.