Fully versus constrained statistical fragmentation of carbon clusters and their heteronuclear derivatives

International audienceThe Microcanonical Metropolis Monte Carlo (MMMC) method has been shown to describe reasonably well fragmentation of clusters composed of identical atomic species. However, this is not so clear in the case of heteronuclear clusters as some regions of phase space might be inaccessible due to the different mobility of the different atomic species, the existence of large isomerization barriers, or the quite different chemical nature of the possible intermediate species. In this paper, we introduce a constrained statistical model that extends the range of applicability of the MMMC method to such mixed clusters. The method is applied to describe fragmentation of isolated clusters with high, moderate, and no heteronuclear character, namely, CnHm, CnN, and Cn clusters for which experimental fragmentation branching ratios are available in the literature. We show that the constrained statistical model describes fairly well fragmentation of CnHm clusters in contrast with the poor description provided by the fully statistical model. The latter model, however, works pretty well for both Cn and CnN clusters, thus showing that the ultimate reason for this discrepancy is the inability of the MMMC method to selectively explore the whole phase space. This conclusion has driven us to predict the fragmentation patterns of the C4N cluster for which experiments are not yet availabl

Charge and energy sharing in the fragmentation of astrophysically relevant carbon clusters

International audienceThe breakup of a molecule following a fast collision with an atom in gas phase can be understood as resulting from two steps. In the first step, the atom transfers energy to the molecule, which is thus electronically and vibrationally excited. In the second step, the molecule decays leading to different fragments, while the initial charge, energy, and angular momentum are conserved. Here, we demonstrate that, by maximizing the entropy of the system under these conservation laws, it is possible to reproduce the fragmentation yields resulting from collision experiments. In particular, our model is applied to investigate fragmentation of excited neutral and singly charged carbon clusters and mono-hydrogenated carbon clusters. These species are commonly exposed to energetic ionizing radiation in the interstellar medium, so understanding the key aspects of their fragmentation, in particular the way energy and charge are shared in the process, can be relevant to get a deeper insight on the evolution of carbonaceous species in the universe

Semiempirical breakdown curves of C2_2N(+)^{(+)} and C3_3N(+)^{(+)}molecules; application to products branching ratios predictions of physical and chemical processes involving these adducts

We constructed semiempirical breakdown curves (BDC) for C$_2$N, C$_3$N, C$_2$N$^+$ and C$_3$N$^+$ molecules. These BDC, which are energy dependent dissociation branching ratios (BR) curves, were used to predict products branching ratios for various processes leading to the formation of C$_2$N$^{(+)}$ and C$_3$N$^{(+)}$ excited adducts. These processes, of astrochemical interest, are neutral-neutral and ion-molecule reactions, dissociative recombination and charge transfer reactions with He$^+$. Model predictions of BR are compared to the literature data and to reported values in the kinetic database for astrochemistry KIDA. With the new BR values, the C$_n$N abundances in cold cores were simulated

Excitation and fragmentation in hight velocity CnN+ - He collisions

info:eu-repo/semantics/nonPublishe

Excitation and fragmentation in high velocity CnN+ - He collisions

We will present measurements and modeling for two aspects of the CnN+ - He collisions (n=1-3, v=2.25 a.u) :cross sections for electronic excitation processes and fragmentation branching ratios for the excited and ionized CnNq+ molecules produced in the collision (q=-1,0,1,2-5).SCOPUS: cp.jinfo:eu-repo/semantics/publishe

Central profile on a transverse slice of phantoms.

<p>Data are normalized to the maximum value intensity of the profile. No abnormality was seen.</p

Mean activity concentration estimated from 15 cm diameter circular Regions of Interest (ROIs) on 15 consecutive slices and accuracy.

<p>Data acquired on the 8 PET systems used in 3D mode. Activity concentration in images and in phantom expressed in kBq/mL. Standard deviation (SD), accuracy and maximum deviation are in %.</p

Mean activity concentration estimated from 15 cm diameter circular Regions of Interest (ROIs) on 15 consecutive slices and accuracy.

<p>Data acquired on the 4 PET systems used in 2D mode. Activity concentration in images and in phantom expressed in kBq/mL. Standard deviation (SD), accuracy and maximum deviation are in %.</p

Observed artefacts on images acquired on uniform phantom.

<p>Display scale is [0; 100%]. A: no artefacts (site 9), B: LOR-RAMLA concentric ring artefacts (site 6), C: FBP concentric ring artefacts (site 4).</p

Dose calibrator reproducibility and accuracy results.

<p>Repeated measurements of certified standard source (⁶⁸Ge) on the dose calibrators of 11 sites. Standard source activity was calculated by applying decay calculation between the calibration date and the measurements date. Measurements expressed in MBq. Standard deviation (SD) and accuracy are in %.</p