Distribution of Articles published per year
(1997 - 2018)
(1997 - 2018)
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Article 1 Read 2 Citations Double photoionization of propylene oxide: A coincidence study of the ejection of a pair of valence-shell electrons Published: 21 March 2018
The Journal of Chemical Physics, doi: 10.1063/1.5024408
Propylene oxide, a favorite target of experimental and theoretical studies of circular dichroism, was recently discovered in interstellar space, further amplifying the attention to its role in the current debate on protobiological homochirality. In the present work, a photoelectron-photoion-photoion coincidence technique, using an ion-imaging detector and tunable synchrotron radiation in the 18.0–37.0 eV energy range, permits us (i) to observe six double ionization fragmentation channels, their relative yields being accounted for about two-thirds by the couple (C2H4+, CH2O+) and one-fifth by (C2H3+, CH3O+); (ii) to measure thresholds for their openings as a function of photon energy; and (iii) to unravel a pronounced bimodality for a kinetic-energy-released distribution, fingerprint of competitive non-adiabatic mechanisms.
Article 0 Reads 1 Citation Anisotropic forces and molecular dynamics Published: 31 January 2018
Rendiconti Lincei. Scienze Fisiche e Naturali, doi: 10.1007/s12210-018-0668-9
The focus of the present work is on the detailed characterization of the most relevant components of the intermolecular interaction, which determine anisotropic force fields driving the molecular dynamics under a variety of conditions. This target is here achieved by combining in a unifying picture the results of different type of experiments, probing complementary aspects of the intermolecular interactions involved. In particular, the analysis of high-resolution scattering data led to an accurate evaluation of the strength and anisotropy of non-covalent interaction components, due to the balance of size (or Pauli) repulsion with dispersion and induction attraction, to which electrostatic contributions must be added. Moreover, for the complete representation of the intermolecular interaction other components of covalent (chemical) nature, mostly affected by charge (electron) transfer effects, must be properly taken into account. Particular attention has been recently devoted to some experimental findings probing in detail the strength, range, anisotropy and role of the charge transfer effects. Obtained results have been important to develop suitable analytical representations for the potential energy surfaces (PESs), tested and improved by exploiting also the comparison with results of ab initio calculations, useful to provide an internally consistent description of the intermolecular interaction both in the most and less stable configurations of the interacting system. The complete and appropriate formulation of the PESs must be then considered crucial not only to describe the dynamics of elementary processes occurring in interstellar medium and in planetary atmospheres, but also to control equilibrium and non-equilibrium phenomena of applied interest, as those occurring in combustion, flames and plasmas.
Article 1 Read 1 Citation Application of Matched-Filter Concepts to Unbiased Selection of Data in Pump-Probe Experiments with Free Electron Lasers Published: 16 June 2017
Applied Sciences, doi: 10.3390/app7060621
Pump-probe experiments are commonly used at Free Electron Lasers (FEL) to elucidate the femtosecond dynamics of atoms, molecules, clusters, liquids and solids. Maximizing the signal-to-noise ratio of the measurements is often a primary need of the experiment, and the aggregation of repeated, rapid, scans of the pump-probe delay is preferable to a single long-lasting scan. The limited availability of beamtime makes it impractical to repeat measurements indiscriminately, and the large, rapid flow of single-shot data that need to be processed and aggregated into a dataset, makes it difficult to assess the quality of a measurement in real time. In post-analysis it is then necessary to devise unbiased criteria to select or reject datasets, and to assign the weight with which they enter the analysis. One such case was the measurement of the lifetime of Intermolecular Coulombic Decay in the weakly-bound neon dimer. We report on the method we used to accomplish this goal for the pump-probe delay scans that constitute the core of the measurement; namely we report on the use of simple auto- and cross-correlation techniques based on the general concept of “matched filter”. We are able to unambiguously assess the signal-to-noise ratio (SNR) of each scan, which then becomes the weight with which a scan enters the average of multiple scans. We also observe a clear gap in the values of SNR, and we discard all the scans below a SNR of 0.45. We are able to generate an average delay scan profile, suitable for further analysis: in our previous work we used it for comparison with theory. Here we argue that the method is sufficiently simple and devoid of human action to be applicable not only in post-analysis, but also for the real-time assessment of the quality of a dataset.
Article 1 Read 2 Citations Single Photon Thermal Ionization of C60 Published: 08 March 2017
Physical Review Letters, doi: 10.1103/PhysRevLett.118.103001
We report on experiments which show that C60 can ionize in an indirect, quasithermal boiloff process after absorption of a single photon. The process involves a large number of incoherently excited valence electrons and yields electron spectra with a Boltzmann distribution with temperatures exceeding 104 K. It is expected to be present for other molecules and clusters with a comparatively large number of valence electrons. The astrophysical consequences are briefly discussed. DOI:https://doi.org/10.1103/PhysRevLett.118.103001 © 2017 American Physical Society
Article 0 Reads 5 Citations The escape of O+ ions from the atmosphere: An explanation of the observed ion density profiles on Mars Published: 01 December 2016
Chemical Physics Letters, doi: 10.1016/j.cplett.2016.09.003
Article 2 Reads 4 Citations Molecular Dications in Planetary Atmospheric Escape Published: 26 August 2016
Atmosphere, doi: 10.3390/atmos7090112
Fundamental properties of multiply charged molecular ions, such as energetics, structure, stability, lifetime and fragmentation dynamics, are relevant to understand and model the behavior of gaseous plasmas as well as ionosphere and astrophysical environments. Experimental determinations of the Kinetic Energy Released (KER) for ions originating from dissociations reactions, induced by Coulomb explosion of doubly charged molecular ions (molecular dications) produced by double photoionization of CO2, N2O and C2H2 molecules of interest in planetary atmospheres, are reported. The KER measurement as a function of the ultraviolet (UV) photon energy in the range of 28–65 eV was extracted from the electron-ion-ion coincidence spectra obtained by using tunable synchrotron radiation coupled with ion imaging techniques at the ELETTRA Synchrotron Light Laboratory Trieste, Italy. These experiments, coupled with a computational analysis based on a Monte Carlo trajectory simulation, allow assessing the probability of escape for simple ionic species in the upper atmosphere of Mars, Venus and Titan. The measured KER in the case of H+, C+, CH+, CH2+, N+, O+, CO+, N2+ and NO+ fragment ions range between 1.0 and 5.5 eV, being large enough to allow these ionic species to participate in the atmospheric escape from such planets into space. In the case of Mars, we suggest a possible explanation for the observed behavior of the O+ and CO22+ ion density profiles.