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We have performed classical molecular dynamics simulations of 3 keV Ar + (C24H12)n(C60)m collisions where (n,m) = (3,2),(1,4),(9,4) and (2,11). The simulated mass spectra of covalently bound reaction products reproduce the main features of the corresponding experimental results reported by Domaracka et al., Phys. Chem. Chem. Phys., 2018, 20, 15052-15060. The present results support their conclusion that molecular growth is mainly driven by knockout where individual atoms are promptly removed in Rutherford type scattering processes. The so formed highly reactive fragments may then bind with neighboring molecules in the clusters producing a rich variety of growth products extending up to sizes containing several hundreds of atoms, and here we show examples of such structures. In addition, knocked out atoms may be absorbed such that e.g. hydrogenated coronene and fullerene molecules are formed. [ABSTRACT FROM AUTHOR]

We have investigated the fragmentation dynamics of the organometallic ferrocene molecule after interaction with multiply charged ions using multicoincidence mass spectrometry and quantum chemistry calculations. We observed unexpected fragmentation dynamics of the two-body breakup channels from ferrocene dications revealing a charge screening effect from the iron atom and delayed fragmentation dynamics. These observations are rationalized through the population of a specific long-lived excited state, where one positive charge is located on each cyclopentadienyl ring. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study of the fragmentation of singly and doubly N-methylated glycine (sarcosine and N,N-dimethyl glycine, respectively) induced by low-energy (keV) O6+ ions. Multicoincidence mass spectrometry techniques and quantum chemistry simulations (ab initio molecular dynamics and density functional theory) allow us to characterise different fragmentation pathways as well as the associated mechanisms. We focus on the fragmentation of doubly ionised species, for which coincidence measurements provide unambiguous information on the origin of the various charged fragments. We have found that single N-methylation leads to a larger variety of fragmentation channels than in no methylation of glycine, while double N-methylation effectively closes many of these fragmentation channels, including some of those appearing in pristine glycine. Importantly, the closure of fragmentation channels in the latter case does not imply a protective effect by the methyl group. [ABSTRACT FROM AUTHOR]

The properties of mixed water–uracil nanoaggregates have been probed by core electron–photoemission measurements to investigate supramolecular assembly in the gas phase driven by weak interactions. The interpretation of the measurements has been assisted by multilevel atomistic simulations, based on semi-empirical tight-binding and DFT-based methods. Our protocol established a positive-feedback loop between experimental and computational techniques, which has enabled a sound and detailed atomistic description of such complex heterogeneous molecular aggregates. Among biomolecules, uracil offers interesting and generalized skeletal features; its structure encompasses an alternation of hydrophilic H-bond donor and acceptor sites and hydrophobic moieties, typical in biomolecular systems, that induces a supramolecular core–shell-like organization of the mixed clusters with a water core and an uracil shell. This structure is far from typical models of both solid-state hydration, with water molecules in defined positions, or liquid solvation, where disconnected uracil molecules are completely surrounded by water. [ABSTRACT FROM AUTHOR]

We propose to combine quantum chemical calculations, statistical mechanical methods, and photoionization and particle collision experiments to unravel the redistribution of internal energy of the furan cation and its dissociation pathways. This approach successfully reproduces the relative intensity of the different fragments as a function of the internal energy of the system in photoelectron–photoion coincidence experiments and the different mass spectra obtained when ions ranging from Ar+ to Xe25+ or electrons are used in collision experiments. It provides deep insights into the redistribution of the internal energy in the ionized molecule and its influence on the dissociation pathways and resulting charged fragments. The present pilot study demonstrates the efficiency of a statistical exchange of excitation energy among various degrees of freedom of the molecule and proves that the proposed approach is mature to be extended to more complex systems. [ABSTRACT FROM AUTHOR]

The laboratory study of prebiotic molecules interacting with solar wind ions is important to understand their role in the emergence of life in the complex context of the astrochemistry of circumstellar environments. In this work, we present the first study of the interaction of hydantoin (C3N2O2H4, 100 a.m.u.) with solar wind minority multi-charged ions: O6+ at 30 keV and He2+ at 8 keV. The fragmentation mass spectra as well as correlation maps resulting from the interaction are presented and discussed in this paper. Prompt and delayed dissociations from metastable states of the ionized molecule have been observed and the corresponding lifetimes measured. Experimental results are completed by quantum Density Functional Theory (DFT) calculations for energies, structures and dynamics (Internal Reaction Coordinates and Dynamic Reaction Coordinates) of the molecule for its different reachable charge states and the major observed fragmentation pathways. These calculations show that the molecule can only support two charges before spontaneously dissociating in agreement with the experimental observations. Calculations also demonstrate that hydantoin's ring opens after double ionization of the molecule which may enhance its reactivity in the background of biological molecule formation in a cirmcumstellar environment. For the major experimentally observed fragmentations (like 44 a.m.u./56 a.m.u. dissociation), Internal Reaction Coordinate (IRC) calculations were performed pointing out for example the important role of hydrogen transfer in the fragmentation processes. [ABSTRACT FROM AUTHOR]

We ionize small mixed pinene–water clusters by electron impact or by using photons after sodium doping and analyze the products by mass spectrometry. Electron ionization results in the formation of pure pinene, mixed pinene–water and protonated water cluster cations. The “fragmentation free” photoionization after sodium doping results into the formation of only water–Na+ clusters with a mean cluster size below that observed after electron ionization. We show that protonated water clusters are formed both directly and indirectly via pinene ionziation. The latter pathway is detailed by ab intio calculations, demonstrating the feasibility of proton transfer from pinene for larger water clusters. In small clusters, the proton transfer reaction is controlled by proton solvation energy and we can thus estimate its value for finite size clusters. The observed stabilization mechanism of water clusters may contribute to the formation of cloud condensation nuclei in the atmosphere. [ABSTRACT FROM AUTHOR]

The fragmentation of glycine (NH2CH2COOH) has been studied by photoelectron–photoion coincidence, PEPICO, experiments at 60 eV photon energy. Glycine practically fragments at the ionization threshold, with the charge being on the H2NCH2+ moiety, due to ejection of an electron from the nitrogen lone pair of the highest occupied molecular orbital. To observe the formation of the complementary cation COOH+ further energy is needed. The flexibility with respect to rotation about the C–C, C–N and C–O bonds makes glycine exist in the gas phase in several conformers of both Cs and C1 point group symmetry in the neutral as well as ion states. The ionization can lead to stabilization of some conformations, rearrangements and, last but not least, H migration between the two moieties. The results of these experiments prove the sensitivity of PEPICO to pin point all these processes. [ABSTRACT FROM AUTHOR]

Ionization, fragmentation and molecular growth have been studied in collisions of 22.5 keV He2+- or 3 keV Ar+-projectiles with pure loosely bound clusters of coronene (C24H12) molecules or with loosely bound mixed C60–C24H12 clusters by using mass spectrometry. The heavier and slower Ar+ projectiles induce prompt knockout–fragmentation – C- and/or H-losses – from individual molecules and highly efficient secondary molecular growth reactions before the clusters disintegrate on picosecond timescales. The lighter and faster He2+ projectiles have a higher charge and the main reactions are then ionization by ions that are not penetrating the clusters. This leads mostly to cluster fragmentation without molecular growth. However, here penetrating collisions may also lead to molecular growth but to a much smaller extent than with 3 keV Ar+. Here we present fragmentation and molecular growth mass distributions with 1 mass unit resolution, which reveals that the same numbers of C- and H-atoms often participate in the formation and breaking of covalent bonds inside the clusters. We find that masses close to those with integer numbers of intact coronene molecules, or with integer numbers of both intact coronene and C60 molecules, are formed where often one or several H-atoms are missing or have been added on. We also find that super-hydrogenated coronene is formed inside the clusters. [ABSTRACT FROM AUTHOR]

The fragmentation of the isolated 5-bromouracil (5BrU) molecule and pure and nano-hydrated 5BrU clusters induced by low energy 12C4+ ions has been studied. A comparison indicates that the environment, on the one hand, protects the system against the complete break-up into small fragments, but, on the other hand, triggers ‘new’ pathways for fragmentation, for example the loss of the OH group. The most striking result is the observation of several series of hydrated fragments in the hydrated cluster case, with water molecules bound to hydrophilic sites of 5BrU. This highlights the strong interaction between 5BrU and water molecules and the blocking of specific fragmentation pathways, such as the loss of the BrC2H group for example. [ABSTRACT FROM AUTHOR]

We report on studies of collisions between 3 keV Ar+ projectile ions and neutral targets of isolated 1,3-butadiene (C4H6) molecules and cold, loosely bound clusters of these molecules. We identify molecular growth processes within the molecular clusters that appears to be driven by knockout processes and that could result in the formation of (aromatic) ring structures. These types of reactions are not unique to specific projectile ions and target molecules, but will occur whenever atoms or ions with suitable masses and kinetic energies collide with aggregates of matter, such as carbonaceous grains in the interstellar medium or aerosol nanoparticles in the atmosphere. [ABSTRACT FROM AUTHOR]

Collisions of 375 keV Xe25+ ions with trapped mass/charge selected poly-anions of the cytochrome C protein (∼12.5 kDa) were studied by coupling a linear quadrupole ion trap with low-energy ion beam facility. Tandem mass spectra were recorded for the protein precursor charge states ranging from −9 to −17. The present work reports the first study of slow highly charged ion collisions with poly-anions. A high signal to noise ratio allowed the study of the intensity of single and multiple electron removal by a projectile, as well as associated neutral losses, as a function of the target charge state. Relative single and double electron detachment cross sections were found to increase with increasing charge state of the precursor anion. The experimental findings are supported by the calculations of the total electron capture cross sections, based on the classical over-the-barrier model, restricted to a simple uniformly charged linear protein structure and a near-end electron capture. [ABSTRACT FROM AUTHOR]

We present a combined experimental and theoretical study of the fragmentation of multiply-charged γ-aminobutyric acid molecules (GABAz+, z = 2, 3) in the gas phase. The combination of ab initio molecular dynamics simulations with multiple-coincidence mass spectrometry techniques allows us to observe and identify doubly-charged fragments in coincidence with another charged moiety. The present results indicate that double and triple electron capture lead to the formation of doubly-charged reactive nitrogen and oxygen species (RNS and ROS) with different probabilities due to the different charge localisation and fragmentation behaviour of GABA2+ and GABA3+. The MD simulations unravel the fast (femtosecond) formation of large doubly charged species, observed on the experimental microsecond timescale. The excess of positive charge is stabilised by the presence of cyclic X-member (X = 3–5) ring structures. 5-Member cyclic molecules can sequentially evaporate neutral moieties, such as H2, H2O and CO2, leading to smaller doubly charged fragments as those observed in the experiments. [ABSTRACT FROM AUTHOR]

The fragmentation of uracil molecules and pure and nano-hydrated uracil clusters by 12C4+ ion impact is investigated. This work focuses on the fragmentation behavior of complex systems and the effect of the environment. On the one hand, it is found that the environment in the form of surrounding uracil or water molecules has a significant influence on the fragmentation dynamics, providing an overall ‘protective’ effect, while on the other hand we observe the opening of specific fragmentation channels. In particular, we report on the first observation of a series of hydrated fragments. This indicates a strong interaction between uracil and water molecules, holding the water clusters bound to the observed molecular fragments. [ABSTRACT FROM AUTHOR]

We present new experimental results on thermal and ion irradiation processing of frozen ammonia–carbon dioxide mixtures. Some mixtures were deposited at low temperatures (T≈ 16 K). Upon warming up to 160 K, complex chemical reactions occur leading to the formation of new molecules and, in particular, of ammonium carbamate. We also show that the same species are produced when water is the dominant species in the ternary mixture with ammonia and carbon dioxide. The samples have been irradiated with 144 keV S9+ ions at 16 K and 50 K. Also in this case, new chemical species are formed as e.g. ammonium formate, CO and OCN−. The results are discussed in the light of their relevance to the chemical evolution of ices in the interstellar medium and in the solar system. In particular, we suggest searching for them among the gas phase species sublimating from grains around young stellar objects and from the cometary nuclei approaching the Sun. [ABSTRACT FROM AUTHOR]

An experimental study of the interaction of highly charged, energetic ions (52 MeV 58Ni13+and 15.7 MeV 16O5+) with mixed H2O : C18O2astrophysical ice analogs at two different temperatures is presented. This analysis aims to simulate the chemical and the physicochemical interactions induced by cosmic rays inside dense, cold astrophysical environments, such as molecular clouds or protostellar clouds as well at the surface of outer solar system bodies. The measurements were performed at the heavy ion accelerator GANIL (Grand Accelerateur National d'Ions Lourds) in Caen, France. The gas samples were deposited onto a CsI substrate at 13 K and 80 K. In situanalysis was performed by a Fourier transform infrared (FTIR) spectrometer at different fluences. Radiolysis yields of the produced species were quantified. The dissociation cross section at 13 K of both H2O and CO2is about 3–4 times smaller when O ions are employed. The ice temperature seems to affect differently each species when the same projectile was employed. The formation cross section at 13 K of molecules such as C18O, CO (with oxygen from water), and H2O2increases when Ni ions are employed. The formation of organic compounds seems to be enhanced by the oxygen projectiles and at lower temperatures. In addition, because the organic production at 13 K is at least 4 times higher than the value at 80 K, we also expect that interstellar ices are more organic-rich than the surfaces of outer solar system bodies. [ABSTRACT FROM AUTHOR]