Intermolecular Coulombic decay after photoionization of carbon-dioxide dimers and oxygen dimers

What is it about?

We have investigated the fragmentation dynamics of CO2 dimer and O2 dimer targets after single photon absorption. More specifically, we focused on the investigation of the symmetric fragmentation channels of the doubly charged dimers. A COLd Target Recoil Ion Momentum Spectroscopy (COLTRIMS) was employed to measure in coincidence the 3D momenta of the emitted ions and electrons. We found that the direct dissociation or autoionization of a single site of a CO2 dimer is suppressed due to the fast relaxation of the dimer via intermolecular Coulombic decay. For both, CO2 dimers and O2 dimers, the kinetic energy of the dissociating ions and of the emitted electrons enabled us to deduce the geometry of the dimers and to coarsely identify the contributing electronic states.

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Why is it important?

Excited systems embedded in an environment can efficiently transfer their energy to neighboring species via an ultrafast de-excitation mechanism known as the Inter-Coulombic Decay (interatomic Coulombic decay or intermolecular Coulombic decay (ICD) depending of the target system under study). Theoretical and experimental investigations have shown that ICD is a very common decay route in nature as it occurs after exciting a loosely bound system (e.g. van der Waals or Hydrogen bonds) by ion, electron, or photon impact. A lot of studies have been carried out on atomic clusters, but significantly less progress is made for molecular clusters. Compared to atomic clusters, new questions arise in the investigation of molecular clusters. For example, how does the higher structural complexity of molecular clusters affect ICD? What other ultrafast relaxation processes can be present, and how do they compete with ICD? In this paper, we go deeper in answering those questions.