Triple F+ ejection from SF6 bombarded by swift ions
TL;DR: In this paper, the angular correlation between each F+ ion is used to figure out the nature of explosion, and the scalar product of three momentum vectors is determined for estimating the co-planarity of all three ejected F+ ions.
Abstract: Many-body explosion of SF3 +6 is investigated by the coincidence momentum imaging technique. Investigation is focused on the F+:F+:F+ dissociative channel. The momentum map of these channels indicates that the loss of neutral F from SF3 +6 occurs in the first step of the break-up followed by Coulomb explosion of the residue. The angular correlation between each F+ ion is used to figure out the nature of explosion. The scalar product of three momentum vectors is determined for estimating the co-planarity of all three ejected F+ ions. From the analysis of angular correlation for coplanar and orthogonal ejection of F+ ions, we conclude that there are two dominant conformations of SF3 +3.
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TL;DR: In this article, the shape and slope of the coincidence islands in the 2D coincidence map were estimated from the geometry of the precursor molecular ion undergoing three-body dissociation and inferred that bent dissociative states are involved in most of the fragmentation channels.
Abstract: Various dissociation channels of OCS
q+ (where q = 2 to 4), formed in the interaction of 5 MeV u-1 Si12+ ion beam with neutral OCS, have been studied using recoil–ion momentum spectroscopy. The concerted and/or sequential nature of dissociation is inferred from the shape and slope of the coincidence islands in the 2D coincidence map. It is observed that the C+ + S+ + O channel results from concerted as well as sequential decay of OCS2+. However the other channels originate purely from the concerted process in which the two terminal fragments (oxygen and sulphur) fly back to back and the central carbon fragment is left with negligible momentum. The kinetic energy release (KER) distributions for all the fragmentation channels arising from the dissociation of OCS
q+ (where q = 2 to 4) have been measured and compared with the available data in the literature. It is observed that the KER values for complete Coulomb fragmentation channels are much smaller than those of incomplete Coulomb fragmentation cases and the KER increases with the increasing charge states of the parent molecular ions. From the momentum correlation map, we estimated the geometry of the precursor molecular ion undergoing three–body dissociation and inferred that bent dissociative states are involved in most of the fragmentation channels of OCS
q+.
7 citations
TL;DR: Quantum chemical computations of field-distorted potential energy curves of SF6 and its molecular ion enable us to rationalize the authors' non-observation ofSF6(+), and have implications for high harmonic generation from SF6 in the few-cycle regime.
Abstract: It is well established that upon ionization of sulphur hexafluoride, the SF6+ ion is never observed in mass spectra. Recent work with ultrashort intense laser pulses has offered indications that when strong optical field are used, the resulting “bond hardening” can induce changes in the potential energy surfaces of molecular cations such that molecular ions that are normally unstable may, indeed, become metastable enough to enable their detection by mass spectrometry. Do intense, ultrashort laser pulses permit formation of SF6+? We have utilized intense pulses of 5 fs, 11 fs, and 22 fs to explore this possibility. Our results are negative: no evidence is discovered for SF6+. However, multiply charged sulphur and fluorine ions from highly charged SF6q+ ions are observed that enable us to resolve the controversy regarding the kinetic energy release accompanying formation of F+ fragment ions. Quantum chemical computations of field-distorted potential energy curves of SF6 and its molecular ion enable us to ra...
5 citations
05 Nov 2012
TL;DR: In this paper, the authors show that the evolution of an unstable molecular ion to an asymptotic many-body state occurs via pathways that are independent of the mechanism of formation of the molecular ion.
Abstract: We show experimentally, by interpretation of coincidence multiparticle momentum maps, that the evolution of an unstable molecular ion to an asymptotic many-body state occurs via pathways that are independent of the mechanism of formation of the molecular ion.
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TL;DR: A new method is developed that takes advantage of the large Coulomb repulsion of the nuclei within molecules rapidly stripped of their electrons to yield geometrical images of individual molecules.
Abstract: Most of our knowledge of the structures of free molecules comes from indirect observations that focus on other properties (for example, energy or mass spectra) that depend on structure. Recently, a new method has been developed that instead yields geometrical images of individual molecules. This method takes advantage of the large Coulomb repulsion of the nuclei within molecules rapidly stripped of their electrons. The first experiments with this new technique have already revealed structural images of several important species, such as positively charged methane ions.
267 citations
TL;DR: In this paper, two experiments producing three-dimensional histograms of time-of-flight correlations have recently been performed at the Daresbury Synchrotron Radiation Source (SRS).
Abstract: Two novel experiments producing three-dimensional histograms of time-of-flight correlations have recently been performed at the Daresbury Synchrotron Radiation Source. In the first, the two photoions from the double ionisation of SF6 were detected; in the second, the photoelectron and the O+ ion from the predissociation of O2+. This technique allows a visual insight into the details of dissociative photoionisation which has not been available previously.
101 citations
TL;DR: An experimental survey of peak shapes in two-parameter mass spectra from charge separation of doubly======charged ions has been combined with Monte-Carlo simulations of peak shape for different mechanisms as discussed by the authors.
Abstract: An experimental survey of peak shapes in two-parameter mass spectra from charge separation of doubly
charged ions has been combined with Monte-Carlo simulations of peak shapes for different mechanisms.
As a result, the major mechanisms, deferred charged separation, secondary dissociation and concerted
explosion, can now be recognised. Finer details and a number of recurrent peculiar peak shapes remain
unexplained.
76 citations
TL;DR: In this article, the dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV.
Abstract: The dynamics of He double ionization by 2 keV electron impact is studied experimentally for a momentum transfer of 0.6 a.u. at excess energies of 10 and 40 eV. Complete sets of fivefold differential cross sections are presented for all electron emission angles in coplanar geometry. Contributions beyond the first Born approximation are identified comparing experimental data with first order convergent close-coupling calculations which are in considerably better agreement with the present experiment than with the earlier measurement of Kheifets et al. [J. Phys. B 32, 5047 (1999)].
74 citations
TL;DR: In this article, the dipole oscillator cross sections for photoabsorption and photofragmentation of SF6 have been obtained over a range of energies up to an equivalent photon energy of 63 eV, from electron-ion coincidence measurements.
Abstract: Dipole oscillator strengths (cross sections) for photoabsorption and photofragmentation of SF6 have been obtained over a range of energies up to an equivalent photon energy of 63 eV, from electron-ion coincidence measurements. The photoionisation efficiency from the ionisation threshold to 63 eV is reported. These results have been combined with photoionisation branching ratios for the six lowest energy states of SF6+ to obtain a model for the dipole-induced fragmentation of valence-ionised SF6. The relative contributions of dissociative and non-dissociative double ionisation have also been investigated.
65 citations