Atomic site sensitive processes in low energy ion-dimer collisions

Electron capture processes for low energy Ar9+ ions colliding on Ar2 dimer targets are investigated, focusing attention on charge sharing as a function of molecule orientation and impact parameter. A preference in charge-asymmetric dissociation channels is observed, with a strong correlation between the projectile scattering angle and the molecular ion orientation. The measurements provide here clear evidences that projectiles distinguish each atom in the target and, that electron capture from near-site atom is favored. Monte Carlo calculations based on the classical over-the-barrier model, with dimer targets represented as two independent atoms, are compared to the data. They give a new insight into the dynamics of the collision by providing, for the di erent electron capture channels, the two-dimensional probability maps p(~b), where ~b is the impact parameter vector in the molecular frame

Interatomic Coulombic Decay as a New Source of Low Energy Electrons in slow Ion-Dimer Collisions

We provide the experimental evidence that the single electron capture process in slow collisions between O$^{3+}$ ions and neon dimer targets leads to an unexpected production of low-energy electrons. This production results from the interatomic Coulombic decay process, subsequent to inner shell single electron capture from one site of the neon dimer. Although pure one-electron capture from inner shell is expected to be negligible in the low collision energy regime investigated here, the electron production due to this process overtakes by one order of magnitude the emission of Auger electrons by the scattered projectiles after double-electron capture. This feature is specific to low charge states of the projectile: similar studies with Xe$^{20+}$ and Ar$^{9+}$ projectiles show no evidence of inner shell single-electron capture. The dependence of the process on the projectile charge state is interpreted using simple calculations based on the classical over the barrier model

Cooling dynamics of carbon cluster anions

A series of ion storage experiments on small carbon cluster anions was conducted to understand size-dependent cooling processes. The laser-induced delayed electron detachment time profile show clear even/odd alternation due to the presence of the electronic cooling. The time evolution of the internal energy distribution was simulated for Cn- (n=4 to 7) with a common procedure taking vibrational and electronic cooling into account

Coulombic and non-Coulombic fragmentation of highly charged benzene

Triple coincidence techniques have been used to measure the kinetic energies released (KER) upon fragmentation of C6Hq+6(q ≥ 4) molecules that are formed in collisions of benzene with 120 keV Ar8+ ions. The measured KER spectrum, which shows definitive structure rather than a continuous profile, is simulated using a simple Coulomb explosion model that accounts for all the permutations and combinations of states from which these fragment ions can be produced from the precursor molecular ion. The simulated spectrum correlates very well with the measurements but for disagreement in the low-KER regime that is attributed to non-Coulombic fragmentation pathways. Thus, in a single spectrum, both non-Coulombic and Coulombic regimes are accessed

Efficient polyyne formation by ns and fs laser-induced breakdown in ethylene and acetylene gas flow

The final publication is available at Elsevier via https://doi.org/10.1016/j.carbon.2019.06.013. © 2019. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/We studied polyyne formation by gas phase laser-induced breakdown in ethylene and acetylene gas flow using ns and fs lasers. The results show that acetylene is the most efficient target molecule for generating polyynes with high selectivity. Of the two lasers, the fs laser achieved higher selectivity for the production of hydrogen-capped polyynes. We also confirmed strong correlations between C2 radical and polyyne production, which have already been observed for larger hydrocarbon targets. In terms of the polyyne formation mechanism, we suggest decomposition of irradiated soot to be a possible pathway, in addition to carbon chain growth by binary collisions