Theory of Ultrafast Interatomic (Intermolecular) Electronic Decay Processes in Polyatomic Clusters

摘要

This thesis is devoted to the study of the non-radiative process of Interatomic (Intermolecular) Coulombic Decay (ICD) in clusters. The aims of this thesis are two-fold: firstly we study ICD in the inner-valence-ionised endohedral fullerene complexes, such as (2s^1)Ne^+@C_60, where it is ultrafast due to the many available decay channels. We investigate the open question of the dependence of the ICD rate on the location of the endohedrally confined ion. Qualitative analysis shows that once the symmetry of the endohedral system is lowered by the departure of a rare gas atom from its equilibrium position in the centre of the cage, multipole plasmon resonances can be excited by energy transfer from the inner-valence-ionised ion to the cage. Nevertheless, our quantitative analytical and ab initio numerical studies lead to the conclusion that the total ICD width is remarkably stable across broad range of geometries. It turns out that the multipole plasmon excitation is negligible and the well-known dipole fullerene plasmon is the one defining the ICD time scale.ududSecondly we focus our attention onto inner-valence vacancies that are not energetic enough to decay via ICD. We propose that under such conditions, an ICD-like electronic process may still be induced by an incident photon. We call the new process single photon laser-enabled ICD (spLEICD). We for the first time investigate spLEICD in a series of van der Waals and hydrogen-bonded clusters. Our results demonstrate that the spLEICD cross-sections in hydrogen-bonded systems are larger than in van der Waals ones, whereas polyatomic van der Waals clusters lead to a more efficient spLEICD process than the van der Waals diatoms. We analyse the dependence of the spLEICD cross-section on the inter-atomic distance in a cluster showing analytically that it obeys the 1/R^6 law at large distances. This analysis is confirmed by our extit{ab initio} numerical calculations. This strong distance-dependence may allow spLEICD to be used as a novel spectroscopic technique for the study of processes which occur in different spatial regions of molecules or clusters.