Fragmentation dynamics of tetrachloromethane molecule induced by highly charged Ar7+-ion impact.

The ion impact multiple ionization and subsequent dissociation of CCl4 is studied using a beam of Ar7+ ion having the energy of about 1 MeV in a linear time- of-flight mass spectrometer, coupled with a position-sensitive detector. The complete, as well as incomplete Coulomb explosion pathways, for CCl4 2+ and CCl4 3+ ions are identified and studied. The kinetic energy release distributions of channels, kinetic energies, and momentum distributions of fragmented ions, as well as neutrals, are also calculated. Possible modes of fragmentation pathways, i.e., concerted and/or sequential, for all the identified channels are studied using Newton diagrams, Dalitz plots, and kinetic energy distributions. The dynamical information and fragmentation pathways were analyzed with the Dalitz plot and Newton diagram for the three-body dissociation channel. The nature of the fragmentation process is further investigated with simulated Dalitz plots and Newton diagrams using the simple classical mechanical model.

Exploring three-body fragmentation of acetylene trication.

The three-body breakup of [C2H2]3+ formed in collision with Xe9+ moving at 0.5 atomic units of velocity is studied by using recoil ion momentum spectroscopy. Three-body breakup channels leading to (H+, C+, CH+) and (H+, H+, C2 +) fragments are observed in the experiment and their kinetic energy release is measured. The breakup into (H+, C+, CH+) occurs via concerted and sequential modes, whereas the breakup into (H+, H+, C2 +) shows only the concerted mode. By collecting events coming exclusively from the sequential breakup leading to (H+, C+, CH+), we have determined the kinetic energy release for the unimolecular fragmentation of the molecular intermediate, [C2H]2+. By using ab initio calculations, the potential energy surface for the lowest electronic state of [C2H]2+ is generated, which shows the existence of a metastable state with two possible dissociation pathways. A discussion on the agreement between our experimental results and these ab initio calculations is presented.

Fragmentation dynamics of CH3Clq+ (q = 2,3): theory and experiment.

A combined theoretical and experimental study of the dissociation of the di- and trication of the CH3Cl molecule has been performed. Experimentally, these multi-charged ions were produced after interactions of a CH3Cl effusive jet with a mono-energetic beam of H+ or Ar9+ projectile ions. Theoretically, we mapped the multi-dimensional potential energy surfaces of CH3Cl2+, H2CClH2+ and CH3Cl3+ species in their electronic ground and electronically excited states using post-Hartree-Fock configuration interaction methods. In addition to the obvious bond-breaking ionic fragments (i.e. H+ + CH2Cl+, H+ + CH2Cl2+ and CH3+ + Cl+), the formation of H2+ (+CHCl+ or CHCl2+), H3+ (+CCl+) and HCl+ (+CH2+) was observed upon bond rearrangement after ion impact of CH3Cl. The interaction strength of the incident projectiles is found to affect the relative yields on the observed dissociation channels, however, it has no effect on the kinetic energy releases of the fragmentation pathways. For the observed dissociation channels, plausible formation mechanisms were proposed. These reaction pathways take place on the ground and/or electronic excited potential energy surfaces of the doubly and triply charged CH3Cl ions, where spin-orbit and vibronic couplings are in action. Moreover, this work suggests that the mechanisms undertaken may depend on the multiply charged ion preparation by valence or inner-shell single photon photoionization, fast ion beam impact or ultrafast intense laser ionization.

Hydrogen migration in triply charged acetylene.

We report on the direct experimental evidence of hydrogen migration in triply charged acetylene. The roaming hydrogen atom in a triply charged molecular ion is counter intuitive. The three body breakup channel C2H2 3+→H++C++CH+ is studied using the technique of recoil ion momentum spectroscopy. The triply charged ion was generated in collisions of the neutral parent with a slow highly charged Xe9+ ion. Three different dissociation pathways have been identified and separated, namely, concerted breakup in an acetylene configuration, concerted breakup in a vinylidene configuration, and sequential breakup via a [C2H]2+ intermediate, and the branching ratio for all three pathways are determined.

A new technique for measurement of subrotational lifetime of molecular ions.

Singly and multiply charged molecular ions are found in diverse environments and hold relevance for a wide range of research areas like combustion chemistry, accelerator physics, atmospheric sciences, plasma physics, astrophysics etc. Molecular dications are of special significance as they can be generated and studied comparatively easily in laboratory experiments. And they have enabled exploration of new and exciting phenomenon such as hydrogen migration, inter-atomic Coulombic decay, plasmonic excitations, orbital tomography etc. The lifetime of a molecular dication is one of its fundamental characteristics, whose measurement contributes to strengthening ab initio calculations and in predicting the concentration of its dissociation products. Most of the already reported lifetimes of molecular dications are in the range of nanoseconds to seconds and metastable states with lifetimes of the order of picoseconds have only been theoretical predicted and an experimental verification is pending. We present a method of measuring subrotational lifetimes of molecular dications formed in three-body sequential breakup of polyatomic molecular precursors. Specifically, we have measured the subrotational lifetime of [Formula: see text] , which is formed as an intermediate in the three-body sequential fragmentation of [Formula: see text]. The lifetime against dissociation is determined to be a fraction of the rotational period of [Formula: see text] and is of the order of few picoseconds. The method proposed is general and is not restricted to triatomic precursors.

Three-body dissociation of OCS3+: Separating sequential and concerted pathways.

Events from the sequential and concerted modes of the fragmentation of OCS3+ that result in coincident detection of fragments C+, O+, and S+ have been separated using a newly proposed representation. An ion beam of 1.8 MeV Xe9+ is used to make the triply charged molecular ion, with the fragments being detected by a recoil ion momentum spectrometer. By separating events belonging exclusively to the sequential mode of breakup, the electronic states of the intermediate molecular ion (CO2+ or CS2+) involved are determined, and from the kinetic energy release spectra, it is shown that the low lying excited states of the parent OCS3+ are responsible for this mechanism. An estimate of branching ratios of events coming from sequential versus concerted mode is presented.

Study of K-line radiation of thick titanium produced in collisions of keV electrons.

The characteristic K-line yields Y(E0) of a pure thick titanium (Z=22) element target are measured for 8-18 keV electron impact and compared with the simulation calculations using PENELOPE code. A fair agreement between experiment and simulation results is found within the existing experimental uncertainty of measurements. The ratio F of indirectly produced characteristic Ti K X-ray yield to its total (directly+indirectly) yield is determined by employing an approximate analytical formulation of Hanson and Cowan (Hanson, H.P., Cowan, D.J., 1961. Phys. Rev. 124, 22-26). It is found that F changes strongly with impact energy E0 for normal angle of incidence in contrast to a mild change predicted by the simulation calculations. Furthermore, experimental and simulation results for peak to effective continuum ratio R of Ti K-line are compared and discussed for the energy range of impact of the present investigation.