The three body fragmentation of methane dication has been studied using the technique of cold target recoil ion momentum spectroscopy. The process is initiated by impact of energetic Ar9+ ions on neutral methane and the data is subsequently collected in coincidence with Ar8+ projectile. By analysing the dissociation channels leading to (H + H+ + CH2+) and (H + H2+ + CH+) fragments, it is concluded that these fragments are formed in a sequential manner via formation of molecular intermediates CH3+ and CH2+ respectively. It is shown that these molecular intermediates carry a few eVs as their internal energies, part of which is released when they emit an H-atom with the open possibility that the final detected fragments may still be internally excited. This was accomplished by analysing the two-steps of the sequential process in their own native frames. For a molecular system having three-dimensional structure, our results prove to be an ideal example to highlight the importance of using native frames for correct interpretation of the obtained results. Our results indicate that the dissociation of methane dication can be a major source of production of H-atoms in addition to H+ fragments with the probability of the two being of similar order.

The PELIICAEN (Platform for the Study of Ion Implantation Controlled and Analyzed at the Nanometric Scale) setup is a unique device, both for all of its in situ ultra-high vacuum equipment (focused ion beam column, secondary electron microscope, atomic force microscope, and scanning tunneling microscope) and for its nanostructuration performances on materials. The setup has been recently equipped with its own electron cyclotron resonance ion sources, a new position-controlled platform using pneumatic vibration insulators, and a fast pulsing device. Its performances were then deeply improved, providing access to a large choice of ions, an adjustable ion implantation depth up to a few hundred nanometers, an image resolution down to 25 nm, and an ion beam size on the sample down to 100 nm. With all this equipment, the PELIICAEN setup is in the international foreground to perform and analyze ion implantation and surface modification.

The ion-induced fragmentation of CH4 2+ into H+ and CH3 + is studied using a cold target recoil ion momentum spectroscopy in coincidence with the charge state of the post-collision projectile. Using constant velocity Ar9+ and N3+, results from four different datasets are presented, with a selection on the final charge state of the projectile (Ar8+ or Ar7+ and N2+ or N+). Three distinct dissociation pathways (I, II, and III) are observed for each dataset, with the mean kinetic energy release values of around 4.7, 5.8, and 7.9 eV, respectively. The electronic states that are populated correspond to electronic configurations (1t2)-2 and (2a1)-1(1t2)-1 of the methane dication, CH4 2+. The relative branching ratios between the three pathways are discussed as a function of the charge state of the post-collision projectile, and a strong correlation with the specific nature of the ion-molecule interaction is found. The existing ab initio calculations have provided an explanation only for pathway II. In this article, we propose an explanation for pathway III, but pathway I still remains unexplained and requires further theoretical efforts. A discussion of the dependence of dissociation on the mode of excitation is presented.

The fragmentation of carbon monoxide dimers induced by collisions with low energy Ar ions is investigated using the COLTRIMS technique. The presence of a neighbor molecule in the dimer serves here as a diagnostic tool to probe the lifetimes of the CO molecular dications resulting from the collision. The existence of metastable states with lifetimes ranging from 2 ps to 200 ns is clearly evidenced experimentally through a sequential 3-body fragmentation of the dimer, whereas fast dissociation channels are observed in a so-called concerted 3-body fragmentation process. The fast fragmentation process leads to a kinetic energy release distribution also observed in collisions with monomer CO targets. This is found in contradiction with the conclusions of a former study attributing this fast process to the perturbation induced by the neighbor molecular ion.

We report on experimental results obtained from collisions of slow highly charged Ar9+ ions with a carbon monoxide dimer (CO)(2) target. A cold target recoil ion momentum spectroscopy setup and a Coulomb explosion imaging approach are used to reconstruct the structure of the CO dimers. The three-dimensional structure is deduced from the two-body and three-body dissociation channels from which both the intermolecular bond length and the relative orientation of the two molecules are determined. For the three-body channels, the experimental data are interpreted with the help of a classical model in which the trajectories of the three emitted fragments are numerically integrated. We measured the equilibrium intermolecular distance to be R-e = 4.2 angstrom. The orientation of both CO molecules with respect to the dimer axis is found to be quasi-isotropic due to the large vibrational temperature of the gas jet.

Van der Waals clusters are weakly bound atomic/molecular systems and are an important medium for understanding micro-environmental chemical phenomena in bio-systems. The presence of neighboring atoms may open channels otherwise forbidden in isolated atoms/molecules. In hydrogen-bond clusters, proton transfer plays a crucial role, which involves mass and charge migration over large distances within the cluster and results in its fragmentation. Here we report an exotic transfer channel involving a heavy N+ ion observed in a doubly charged cluster produced by 1 MeV Ne8+ ions: (N2Ar)2+→N++NAr+. The neighboring Ar atom decreases the [Formula: see text] barrier height and width, resulting in significant shorter lifetimes of the metastable molecular ion state [Formula: see text]([Formula: see text]). Consequently, the breakup of the covalent N+-N+ bond, the tunneling out of the N+ ion from the [Formula: see text] potential well, as well as the formation of an N-Ar+ bound system take place almost simultaneously, resulting in a Coulomb explosion of N+ and NAr+ ion pairs.

Synopsis The Coulombic explosion of multi-charged (CO)3q+ molecular ions produced in low energy collisions with Ar9+ projectiles was investigated using recoil ion momentum spectrometry (RIMS). A preliminary analysis of the data clearly shows a dominant triangular cyclic structure. Events that may correspond to a linear chain are also observed, but the latter could as well originate from false coincidences, associated to the fragmentation of dimers. A careful analysis of this source of background is proposed to disentangle trimer fragmentation events from false coincidences.

We report our results from collisions between multiply charged Ar9+ and Xe20+ ions and atomic or molecular dimers. In such systems, the presence of a surrounding environment may give rise to specific energy relaxation mechanisms. For atomic dimers, we found that the low electron mobility along the dimer results in an asymmetry in the charge repartition among the two ionic fragments. Specific relaxation process such as radiative charge transfer has also been identified. For molecular nitrogen dimers, the role of the environment on molecular fragmentation has been investigated by comparing the fragmentation of multiply ionized monomers N-2(2+) and dimers (N-2)(2)((3)+).

Synopsis Weakly bound atomic or molecular clusters are of growing interest in the fields of atmospheric science, hadron-therapy or astrophysics. We will present our recent experimental results on the fragmentation of diatomic molecular dimers after irradiation by highly charged ions. For (N2)2 dimers, the measured KER spectrum is very similar to the one of the N2 monomers but is globally shifted towards higher energies. Moreover, sequential dissociation of the (CO)2 dimers has been observed when metastable states of the CO2+ dications are populated.

1 CIMAP, CEA-CNRS-ENSICAEN-UNICAEN, Normandie Université, BP5133, F-14050 Caen Cedex 04, France 2 Normandie Univ, ENSICAEN, UNICAEN, CNRS/IN2P3, LPC Caen, 14000 Caen, France 3 Chemical Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA-94720, USA 4 Department of Chemistry, Tokyo Metropolitan University, 1-1 Minami-Osawa, Hachioji, Tokyo, Japan 192-0397 5 Inter University Accelerator Center, Aruna Asaf Ali Marg, New Delhi 110067, India

We present a combined theoretical and experimental study of primary and postcollision mechanisms involved when colliding low-energy multiply charged ions with van der Waals dimers. The collision dynamics is investigated using a classical calculation based on theCoulombicOver-the-Barrier Model adapted to rare gas dimer targets. Despite its simplicity, the model predictions are found in very good agreement with experimental results obtained using COLd Target Recoil Ion Momentum Spectroscopy, both for the relative yields of the different relaxation processes and for the associated transverse momentum exchange distributions between the projectile and the target. This agreement shows to what extent van der Waals dimers can be assimilated to independent atoms.

In a combined theoretical and experimental study, we give evidence that the self-organized electric potential in tapered glass capillaries has the strength to focus a low-energy ion beam. Similar to Einzel lenses, the on-axis injected beam is focused by an axis-symmetric potential, generated by the charge accumulated in the insulating capillary. We argue that for capillaries with large aspect ratio, the mechanism responsible for the focusing in our experiment is different from the one shown in earlier experiments. We found that the potential inside the capillary had to reach about 70% of the extraction potential of the ion source in order to be strong enough to focus the beam through the capillary. With increasing injected current intensities, the transmitted current density is shown to increase up to a factor 10 with respect to the injected one. An original experimental setup is used to monitor the accumulated total charge in the capillary linking the latter to the transmitted fraction of the beam. This way, we can clearly identify the different stages of the transmission in real time, and in particular the Coulomb blocking, and explain why it occurred inevitable in this setup. The experimental data are corroborated by our simulations, which allow a valuable and comprehensive insight into the dynamics of the self-organized Coulomb potential. The latter controls the focusing effect and explains many features such as why the transmitted fraction increases with the injected intensity.

The angular distribution of fragment emission with respect to the incoming beam direction is measured. In case of two body breakup of di-cationic molecular ions, such as D2O2+ and C2H22+, a strong anisotropy is observed when one of the fragments is an H+ or D+. These molecular ions were produced by impact of slow highly charged ions on neutral species. The technique of recoil ion momentum spectroscopy was used to measure the complete momentum vectors of all fragments in coincidence.

We report studies on stabilities of dimer and trimer of polycyclic aromatic hydrocarbon PAH in a small electrostatic storage device. Different nslaser energies were used at different time delays as the probe to determine the dissociation energy. The effect of dehydrogenation on the stability is also studied.

Fragmentation of molecular nitrogen dimers (N_{2})_{2} induced by collision with low energy 90 keV Ar^{9+} ions is studied to evidence the influence of a molecular environment on the fragmentation dynamics of N_{2} cations. Following the capture of three or four electrons from the dimer, the three-body N_{2}^{+}+N^{m+}+N^{n+} [with (m,n)=(1,1) or (1, 2)] fragmentation channels provide clean experimental cases where molecular fragmentation may occur in the presence of a neighbor molecular cation. The effect of the environment on the fragmentation dynamics within the dimer is investigated through the comparison of the kinetic energy release (KER) spectra for these three-body channels and for isolated N_{2}^{(m+n)+} monomer cations. The corresponding KER spectra exhibit energy shifts of the order of 10 eV, attributed to the deformation of the N^{m+}+N^{n+} potential energy curves in the presence of the neighboring N_{2}^{+} cation. The KER structures remain unchanged, indicating that the primary collision process is not significantly affected by the presence of a neighbor molecule.

Insulating glass capillaries have been shown to lead to ion transmission without any change in either the ion charge state or in the ion kinetic energy. This surprising process has been attributed to a self-organized distribution of charge patches creating the necessary guiding electric potential on the capillary walls. By the use of our original electrometer, it has been possible to measure and monitor simultaneously and in a nondestructive way the electric potential and the transmitted beam intensity during the charging up by an ${\mathrm{Ar}}^{+}$ ion beam. We show that glass microcapillaries can reach potentials higher than 500 V, even in the case of singly charged ions, opening the possibility of high transmission rates and providing a renewed sight into ion beam transport by tapered capillaries. The setup, also suitable for the determination of leakage currents governing the capillary potential dynamics, allowed one to evidence that secondary electrons may strongly affect the rise of the capillary potential and consequently avoid Coulomb blocking of the beam transmission across insulating capillaries.

Silicates are the dominant surface material of many Solar System objects, which are exposed to ion bombardment by solar wind ions and cosmic rays. Induced physico-chemical processes include sputtering which can contribute to the formation of an exosphere. We have measured sputtering yields and velocity spectra of secondary ions ejected from nepheline, an aluminosilicate thought to be a good analogue for Mercury's surface, as a laboratory approach to understand the evolution of silicate surfaces and the presence of Na and K vapor in the exosphere. Experiments were performed with highly charged ion beams (keV/u–MeV/u) delivered by GANIL using an imaging XY-TOF-SIMS device under UHV conditions. The fluence dependence of sputtering yields gives information about the evolution of surface stoichiometry during irradiation. From the energy distributions N(E) of sputtered particles, the fraction of particles which could escape from the gravitational field of Mercury, and of those falling back and possibly contributing to populate the exosphere can be roughly estimated.