We measured the Q-value and the scattering angle distributions for non-dissociative state selective single electron capture in collisions of 7.5 keV H$^+$ and 15 keV H$_2^+$ with He. The experimental data are compared with semiclassical close-coupling calculations and predictions from the classical trajectory Monte Carlo simulations. By analogy with Fraunhofer diffraction, we also developed a toy model to reconstruct an imaginary screen that reflects the reaction impact-parameter dependence, in channels where the magnetic quantum number remains unchanged. It is well established that H$_2^+$ acts as a molecular double-slit in scattering processes. By demodulating the Young's double-slit-type interference pattern, we extracted the individual slit diffraction pattern of H$_2^+$ and compared it with that of the H$^+$ atomic single-slit. For ground state electron capture, we found that the single and the double slit diffraction patterns have equal fringe width, whereas for excited state electron capture, diffraction patterns are quite different.

In the present study, we compare the absolute double differential cross-sections (DDCS) of electron emission from methane molecule by the impact of two projectiles at same velocities but different charge states, i.e., proton and He ^2+ ions having energy of 100 keV/u. Methane is the simplest multi-electron hydrocarbon molecule. The electron DDCS are measured using the electron spectroscopy technique for emitted electron energy range of 0.1 eV–360 eV at different scattering angles. The single differential cross-section (SDCS) and the total cross-section (TCS) are obtained by integrating DDCS and SDCS, respectively. The continuum distorted wave-eikonal initial state model (CDW-EIS), using molecular orbital (MO) approach for target description, has been used to compare with the measurements. The chosen collision systems allow us to test the well-developed model at the border of the intermediate-to-fast collision regime (with projectile velocity ( v_p ) = 2 a.u.) and at slightly higher perturbations for doubly charged He-ion impact. It helps to explore the limit of its applicability. In the energy distribution spectrum, the agreement with theory looks better for the H ^+ data but shows drastic deviations for the doubly charged He ^2+ data. The deviation increased even more towards the extreme backward angles, perhaps owing to the fact that the backward emission is highly influenced by back scattering from the molecule. The TCS is, however, well reproduced by the CDW-EIS. The angular distribution and the forward-to-backward DDCS ratio indicating the dynamics of post collision interaction (PCI) show gross and drastic deviation from the model, particularly for the He-ions. The DDCS ratios obtained for He ^2+ and protons bring out the limitations of the model for the two-center electron emission (TCEE) regime of the electron spectrum.

We present an experimental investigation of the state-selective single-electron capture process in 10 and 40 keV NO2+ + {He,H2} collision systems. Using the cold target recoil ion momentum spectroscopy technique, we measure the non-dissociative state populations following electron capture and the corresponding scattering angle distributions. To interpret the observed structures in the scattering angle distributions, we estimated the impact parameter dependence using a 'toy' model inspired by Fraunhofer matter-wave diffraction from a circular aperture. This model estimated the wavefront alteration in the scattering processes and provided a qualitative insight into the role of the molecular double-slit in the state-selective electron capture process.

Abstract We present a comprehensive study on the multiple ionization and fragmentation of a PAH molecule, coronene (C24H12) with special emphasis on dehydrogenation and multiple ionization, in collisions with protons of energy 100-300 keV, relevant for solar wind. Dehydrogenetaion i.e. loss of H-atoms or H2 are also investigated from the measured spectra of cation, di-cation and tri-cation using a Wiley-McLaren-type time-of-flight mass spectrometer. H2 loss is found to be dominant mechanism over single H-loss in, with up to three molecules being lost. This observation is in line with some of the predictions and may provide important inputs towards the astrochemistry regarding the abundance of H2 in the inter stellar medium. The relative cross sections were determined for the recoil ion production. The ionization cross sections and their ratios were also calculated theoretically using continuum distorted wave–eikonal initial state (CDW-EIS) model and compared with the experimental results. The ratios of double-to-single and triple-to-single charged recoil-ions are found to be much higher compared to those for the gaseous atoms. The significant enhancement in the yields of di-cation (and tri-cation) may be related to multielectron correlation and plasmonic behaviour.

In the present study, we report the experimentally measured double differential cross section (DDCS) of electron emission from methane (CH4) in collisions with proton beams of three different energies i.e. 75, 150 and 300 keV covering intermediate to fast collision regime, which is quite a sensitive energy range to test the theoretical models. The energy and angular distributions of the DDCS are compared with the theoretical calculation based on the continuum-distorted-wave-eikonal-initial-state (CDW-EIS) model. Two different approximations of the CDW-EIS model are implemented, such as, complete neglect of differential overlap (CNDO) and molecular orbital (MO) approach with two different internuclear distance scaling parameters. In general, the qualitative agreement with the experimental data is found to be better for the MO based model with the scaling parameter value d = 1.0, where 'd' is the theoretical scaling parameter related to the C-H internuclear distance. The single differential cross section (SDCS) and the total cross section (TCS) are deduced from the measured DDCS data. The TCS data shows a decreasing trend with projectile energy, which qualitatively follows the existing data which seems to be higher than the present data. The CDW-EIS (MO) with d=1.0 provides a better agreement with the present TCS data. The post-collision interaction process is also probed by analyzing the forward-backward asymmetry as a function of projectile velocity ( vp), electron velocity ( ve) and the scaled velocity ( vp/ve). The CDW-EIS (MO) model predicts a much steeper fall in the asymmetry compared to the experimental slope. This indicates the partial inability of the CDW-EIS model to predict the influence of the two-center effect correctly in the intermediate-to-fast collisions.

Multiple ionization and fragmentation of a large polycyclic aromatic hydrocarbon (PAH) molecule, i.e. coronene (C 24 H 12 ) under the impact of fast (1.5–5.5 MeV/u) O ions are investigated as a function of the perturbation strength (charge state/velocity). The mass spectra from a Wiley-McLaren type time-of-flight mass spectrometer have been measured for different energy and charge state of the projectile. We have observed a dramatically large enhancement in the ratios (2+/1+) of doubly-to-singly charged parent recoil ion yields and similarly in the 3+/1+ recoil ion ratios which are discussed in the context of highly correlated electrons in the PAH and resulting collective excitations in coronene. These ratios are well-reproduced by a classical over-the-barrier (COB) model. The nearly linear dependence of the measured cross-sections on the projectile charge state is linked to the collective plasmon excitation in the coronene molecule based on a model originally developed for the fullerene. The measured absolute cross sections, obtained using a novel normalization technique, based on complementary electron spectroscopy experiments, are compared with the CTMC-COB (Classical trajectory Monte Carlo calculations including classical over-the-barrier model), as well as with a more sophisticated state-of-the-art quantum-mechanical CDW-EIS (continuum distorted wave eikonal initial state) model. The absolute partial cross sections for the singly, doubly and triply ionized recoil-ions exhibit a good quantitative agreement with the CDW-EIS calculations - a step toward the development of quantum mechanical model for such large molecule. The present observation will also have implications towards the study of astrochemistry of the interstellar medium.

Results of our experimental study of the 24Mg(p,γ)25Al resonance reaction at E=plab223 keV are presented. The proton beam energy is varied from 220 to 265 keV. An evaporated Mg target with thick Ta backing is used. We remeasure a mean lifetime of τ=6.04−2.65+3.03 fs for the E=x2485.3 keV level of 25Al, using Doppler shift attenuation (DSA) method. Three most successfully used empirical effective interactions developed for the sd shell by Wildenthal (w), Chung-Wildenthal (cw) and Preedom-Wildenthal (pw), are utilized to calculate energy spectra, spectroscopic factors, beta decay properties, transition probabilities and the lifetime of the resonance state in 25Al within the framework of nuclear shell model. The theoretical results agree reasonably well with the experimental data. However, a detailed study for each set to identify the most preferred interaction for this nucleus is performed. Calculated lifetimes using two of the interactions (w, cw) agree better with the central value of the experimental lifetime of the resonance state measured in the present work.

We present an experimental study of multiple-electron capture-induced fragmentation dynamics of Ar2m+ (4 ≤m≤ 7) dimer ions in 4 keV/u Ar8+–Ar2 collisions. The fragment recoil ion pairs and the charge-changing projectiles are coincidentally measured using a double coincidence technique. The branching ratios between the different charge-sharing fragmentation channels show an inherent enhancement of the asymmetric channels. The kinetic energy release (KER) distributions for the associated electron capture process show a shift in the mean KER values toward the higher side with increasing capture stabilization. The interplay between the different projectile autoionization processes sheds light on the energy depositions to the system during collisions. The Coulomb potential energy curves give a physical insight into the role of the projectile final states in the dimer fragmentation dynamics. The dimer-axis orientation-dependent cross sections for the asymmetric fragmentation channels reveal a forward–backward asymmetry that arises from the geometry of the collision system. Our findings thus give insight into the impact parameter-controlled fragmentation dynamics of multiply charged Ar2m+ dimer ions in highly charged ion–dimer slow collisions.

Coronene molecules have been bombarded with protons of energy ranging from 100 to 300 keV. The time of flight mass spectra have been recorded using a two stage Wiley McLaren type spectrometer. A significant enhancement in the yields of doubly and triply ionized recoil ions is observed compared to the singly ionized ones. The single, double and triple ionization cross sections are also calculated theoretically using the continuum distorted wave eikonal initial state (CDW EIS) and are compared with the experimental results. The experimental ratios of yields of double to single charged and triple to single charged recoil ions are found to be much higher compared to those for the gaseous atoms. Evaporation peaks corresponding to the loss of several neutral C2H2 molecules are observed for singly, doubly and triply charged coronene recoil ions. Multi fragmentation peaks corresponding to smaller masses of carbohydrates CnHx (n = 3 to 7), appear in the spectra due to higher energy transfer from the projectile to the molecule. The yields of evaporation and fragment products exhibit a pronounced dependence on projectile energy, with a significant decrease observed at higher energies. Dehydrogenetaion i.e. loss of H atoms or H2 molecules are also investigated from the measured spectra. It is observed that hydrogen molecule losses are preferred over H loss in the cation and dication coronene peak structures, with up to three molecules being lost. This observation is in line with some of the predictions and may provide important inputs towards the astrochemistry regarding the observed abundance of H2 in the inter stellar medium.

We have measured the absolute cross section for L-MM Auger electron emission in chlorinated methanes and benzene chloride molecules in collision with keV energy protons. The measurements have been performed with four different chlorine containing organic molecules viz CCl4, CHCl3, CH2Cl2 and C6H5Cl. We have measured the angular distribution of chlorine L-MM Auger electrons at backward emission angles (90° – 150°). The angular distribution shows an isotropic character. We also studied the projectile energy dependence of the total L-MM Auger yield for proton energy ranging from 125 keV to 275 keV. Carbon K-LL Auger yield was also obtained in the same experiments.

In low energy ion-molecule collisions, electron capture is one of the most important channels. A new experimental setup was developed to study the electron capture process using low-energy ion beams extracted from an electron cyclotron resonance (ECR) plasma-based ion accelerator. Experiments were carried out with the proton beam colliding with water vapor in the energy range of 70–300 keV. Capture events were detected using a position-sensitive detection system comprising micro channel plates (MCPs) and a delay line detector (DLD). These e-capture events can be a result of pure capture reactions as well as transfer ionization. The capture cross section was found to decrease sharply with the beam energy and agreed well with previous measurements. The setup was also used to detect the events that gave rise to the single and multiple e-capture (integrated over all recoil-ion charge states) of C4+ ions. The capture cross-sections for one, two, three, and four electrons were measured for 100 keV C4+ ions. The ratio of multielectron capture yield to that for single e-capture decreased with the number of captured electrons.

The energy and angular distribution of electron emission from a RNA base molecule, uracil ( C 4 H 4 N 2 O 2 ), are investigated in collisions with 2.5-MeV/u Si 12+ ions under high perturbation strength. The absolute double differential cross sections (DDCS) are measured using electron spectroscopy for emission angles between 20° to 160° in the electron energy range 1-620 eV. The single differential cross sections (SDCS) are evaluated by integrating the DDCS over emission angles or energies. The measured cross sections (DDCS and SDCS) are compared with the state-of-the-art continuum distorted wave-eikonal initial state (CDW-EIS) theoretical model. The DDCS obtained by the CDW-EIS is found to provide better agreement with the measurements in the backward angles. With an increase in perturbation strength from 0.5 to 1.19 a.u., the DDCS is found to increase by 10 times in comparison to the earlier reported uracil data for 3.5-MeV/u bare C-ions [Phys. Rev. A 87, 032716 (2013)]. The significant enhancement in the TCS is found for the total cross section in case of Si 12+ ions over that predicted by a scaling law as derived for lower charge state projectiles. The forward-backward angular asymmetry is found to increase monotonically with the velocity of emitted electrons and shows very good agreement with the model. For a comparative study, the DDCS is also measured for oxygen molecule using same ion impact, which is found to be about ten times lower than that for the uracil. The forward-backward angular asymmetry for oxygen is found to be almost the same as uracil.

We measure double differential cross sections (DDCS) of electrons emitted from CH4 molecules in collisions with 250 keV protons. The projectile ions are obtained from a 400 kV electron cyclotron resonance-based ion accelerator (ECRIA). We study the energy and angular distributions of the electron DDCS. The observed double and single differential and the total cross section are compared with the state-of-the-art continuum distorted wave eikonal initial state (CDW-EIS) model predictions. Two different approaches are used considering the different target descriptions: complete neglect of differential overlap (CNDO) and molecular orbital (MO) approximations. The MO model uses two different scaling parameters (d = 0.7 and 1.0). In the energy distribution of the DDCS, the carbon KLL Auger line is also observed at 240 eV. The single differential cross section (SDCS) and total cross section (TCS) are derived. Both the MO-based CDW-EIS models are in good agreement with the experimental results; however, the CNDO approach overestimates the data.

We report the development of a supersonic jet assembly to study electron transfer collisions with atoms, molecules, and van der Waals clusters. A comparative study of Ar monomer and dimer cations is presented for different capture-associated channels with a 2.5 keV/u O2+ projectile beam. For the Ar+ + Ar+ fragmentation channel, the interatomic relaxation channels are discussed. The vacancies of the dimer single site or double site show the dependence on capture mechanisms. In the Ar2+ + Ar+ fragmentation channel, double capture, in addition to the single ionization process, dominates. The orientation effect reflects the maximum yield at around 50 and 130 degrees, and angular distributions are nearly symmetric about the axis perpendicular to the dimer axis.

We report the characterisation of the efficiency and resolution of a high-resolution bent crystal spectrometer under Johannson geometry, using ray-tracing simulations. The spectral resolution is measured experimentally from electron-beam and fast ion-beam interactions with thin solid foils. The X-rays emitted by target atoms as well as projectile ions are studied. The results of the ray-tracing simulations are in very good agreement with the beam-foil spectroscopy experiments. The geometrical factors affecting the resolution are also discussed in detail. We also characterise the detection efficiency of the spectrometer by simultaneous measurements of X-rays using a semiconductor detector, i.e. Si(Li) detector, with known detection efficiency. These results are also compared with the ray-tracing simulation results.

We study the electron capture-induced fragmentation of N-2 molecules upon impact with Ar8+ projectiles at collision velocities 0.4 and 1.0 a.u. The recoil ions and the charge-changing projectiles are recorded in coincidence by combining a cold target recoil ion momentum spectrometer with a projectile final charge state analyzer. The relative contributions between projectile autoionizations and radiative decays are measured for the individual dissociation pairs. The reaction windows and corresponding final projectile states for multiple-electron capture processes are estimated using the extended classical over-the-barrier model. The various dissociation pairs' kinetic energy release (KER) is measured for the associated capture processes. For the dissociating N-2(m+) (2 <= m <= 6) molecular ions, the mean KER values shifted to higher values as capture stabilization increased. The populations of the higher KER regions are explained by the recapture of the loosely bound electrons into the target highly excited states. A simple classical capture model is employed to understand the role of the different projectile states on the KER distributions (KERDs). Our findings thus demonstrate the collision velocity dependence of the projectile's final state populations and its impact on the KERDs in the highly perturbative regime.

We have studied the absolute double differential cross section (DDCS) of electrons ejected from the methane molecule (CH4) under the impact of highly charged fast projectile ions. The energy and angular distributions of electrons have been measured in interactions with 70 MeV Si12+ ions. These DDCS data together with the derived single differential cross sections and the total cross section (TCS) have been compared with predictions of the continuum distorted wave-eikonal initial state model using different approaches for the molecular orbitals. It has been found that the theories overestimate the measured DDCS values at low ejection energies, which may indicate shortcomings of the model in the case of strong perturbation. At the same time, applying the model to a previous measurement using fast C ions having a lower perturbation strength, excellent agreements have been obtained with the experimental data. Considering the scaling properties, the available TCS data have been plotted with a scaled parameter, namely the perturbation strength, q/v (where q= charge state, v=velocity of the projectile). The KLL Auger e-emission as well as the KLL hyper-satellite peaks are analyzed for different emission angles. The double K-vacancy production shows a considerable enhancement i.e. 37% of the single production cross section which is consistent with some of the recent experiments on K-ionization using x-ray techniques.

We report on the measurement of absolute cross sections and angular distribution of electron emission in the K-LL Auger region, upon electron impact ionization of molecular (CH4 and N-2) and atomic (Ne) targets. Differential cross sections in the K-LL Auger energy range were measured at 6 keV and 8 keV impact energies. The angular distribution of the K-LL Auger yield is shown to be isotropic for all the three targets. Total K-LL Auger emission cross sections were estimated by integrating the measured differential cross sections over the entire energy and angular range. The estimated cross sections are in good agreement with the theoretical estimates.