Resumen de Coherence in molecular photoionization
We present a theoretical study of light-induced phenomena in gas-phase molecules. We explore the physical phenomena arising in two distinct contexts: using synchrotron radiation and ultrashort laser pulses. This theoretical work has been done in close collaboration with Piero Decleva, from Universit a di Trieste. We rst present a study of inner-shell photoionization of diatomic (CO) and small polyatomic (CF4, BF3) molecules at high photoelectron energies performed in collaboration with the experimental the groups of Edwin Kukk (Turku University), Catalin Miron (Soleil Synchrotron), Kiyosi Ueda (SPring8 Synchrotron) and Thomas Darrah Thomas (Oregon State University). The combination of state-of-the-art Density Functional Theory (DFT)-like calculations capable to describe photoionization accounting for the nuclear degrees of freedom together with high-resolution third-generation synchrotron facilities has enabled the investigation of non-Franck-Condon e ects observable in vibrationally resolved photoionization measurements. We demonstrate that the nuclear response to intramolecular electron di raction is observable and can be used to obtain structural information. As a proof-of-principle, by using the DFT calculations as an analysis tool to t the experimental data, we have accurately determined the equilibrium distance of the CO molecule and the bond contraction that takes place upon C 1s ionization. This is a surplus of photoelectron spectroscopy with respect to more conventional spectroscopic techniques, which usually can only provide structural information of neutral molecular species. Furthermore, we have explored the di erent phenomenon arising when an electron is emitted from a delocalized orbital: multicenter emission. The results on molecular uorine coming from our numerical simulations are in good qualitative agreement with those provided by the simple formula proposed by Cohen and Fano in the sixties. We have employed the same DFT-based methodology together with timedependent rst-order perturbation theory and a reduced density matrix formalism to report the rst demonstration of purely electron dynamics in a biological molecule: the amino acid phenylalanine, in collaboration with the experimental groups of Mauro Nisoli (Politecnico di Milano), Luca Poletto (IFN-CNR, Padova) and Jason Greenwood (Queen's University, Belfast). The use of attosecond pulses in combination with novel detection techniques has enabled the capture of purely electron motion at its intrinsic time scale. Because of their wide energy bandwidth, attosecond pulses are ideal sources to generate coherent superpositions of states, triggering an ultrafast electronic response that can be later tracked with attosecond resolution. Our theoretical study enabled to interpret the experimental ndings in terms of charge migration, thus con rming the rst observation of purely electron dynamics in a biomolecule. The work presented here has been extended to treat the amino acids glycine and tryptophan, which has allowed the investigation of radical substitution e ects in the charge migration mechanism
