• What is the problem/issue being addressed?
Currently, the structure of nanodroplets is probed using mass spectrometry. Droplets are ionized (usually by electron impact) and undergo fragmentation. However, the fragmentation dynamics is fairly complex and determining the structure of the droplets from the mass spectrum is not straightforward. Several theoretical works have focused on the structure and the dynamics of pure and doped droplets, either in the description of the droplets formation and pick-up processes or on understanding the fragmentation dynamics. An obstacle in modeling the latter is that the number of charges and the distances between them are not known. In the case of multiple ionization the explosion of the droplets depends strongly on the distance between the charges. Models have thus to rely on some kind of statistical averaging over the distances. Even in the case of singly-ionized droplets, simulating the fragmentation dynamics is difficult since important quantum effects are expected. A better control of the number of charges and their location is therefore desirable. One of the goals of this project is to investigate Interatomic Coulombic Decay (ICD) as means to control the charges in nanodroplets.
• Why is it important for society?
The project is primarily of fundamental importance and no direct impact for society is expected. However, helium nanodroplets are widely used in many applications. Our project establishes a new spectroscopic tool to measure the size of nanodroplets. A better characterization of the droplets contributes to the progress in these applications.
• What are the overall objectives?
The aim of the project is to assess the applicability of Interatomic Coulombic decay as a spectroscopic tool for probing the structure of nanodroplets. To answer this question, the electronic decay and subsequent fragmentation dynamics of pure helium nanodroplets of different sizes have been simulated from first principles. From these simulations, the kinetic-energy distributions (KER spectra) of the ionic fragments, which are the main observables, are obtained and compared with available experimental data in order to establish a relationship between the observables and the size of the initial droplets. It is expected that this project provides enough detailed information to propose a new spectroscopic tool for characterizing nanodroplets. Moreover, this investigation will be a first step towards the study of doped nanodroplets. ICD spectroscopy may help to determine the number of the dopants as well as their location and thus lead to a better control of the isolation technique.
