Pushing the boundaries of quantum knowledge
Quantum mechanical interference is an effect fundamental to a wide range of processes and applications in different branches of physics. For many processes in nature it causes dramatic counterintuitive observations, and fundamental research is needed to gain detailed understanding of this effect. Interference effects in molecular spectroscopy are realisations of the macroscopic double-slit experiment on the microscopic scale. Previous studies had demonstrated that coherent population and decay of overlapping vibrational resonances – known as lifetime vibrational interference (LVI) – is the dominant effect in solid-angle-averaged decay spectra. Meanwhile, there had been very little previous study into electronic state interference (ESI) in molecules. This consists of a coherent population of final decay states via different intermediate electronic resonances and via direct photo-ionisation. The Interference project led detailed theoretical and experimental investigations into different types of interference effects in the decay of inner-shell excited molecules. Research had shown that angularly resolved decay spectra of core-excited molecules provide conceptually new fundamental information on interference effects of both types. Project work concentrated on core-excitations of carbon monoxide (CO) and nitrogen monoxide (NO) molecules, with experiments performed by means of photon-induced fluorescence spectroscopy. The theory and computational approach for calculating angular distributions of the Auger electrons and fluorescence photons emitted by randomly oriented diatomic molecules excited by polarised radiation was developed within the project. The project showed that angularly resolved decay spectra of core-excited CO are much more sensitive to LVI and ESI than the angularly unresolved ones. All scientific results from the project were published in journals, presented at scientific conferences and reported to a wide society of specialists. The initiative also led to new international collaboration and considerably advanced this branch of physics. The outcomes could be used to stimulate further activities in the field and extend knowledge on fundamental interference effects.