Breakup of theSF63+photoion revealed by momentum correlation between fragments (original) (raw)
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The Journal of Chemical Physics, 2004
The partial ionization cross section for the formation of SF3+ fragment ions following electron impact on SF6 is known to have a pronounced structure in the cross section curve slightly above 40 eV. We used the mass-analyzed ion kinetic energy (MIKE) scan technique to demonstrate the presence of a channel contributing to the SF3+ partial ionization cross section that we attribute to the Coulomb explosion of doubly charged metastable SF42+ ions into two singly charged ions SF3+ and F+, with a threshold energy of about 45.5 eV. Thus the observed unusual shape of the SF3+ partial ionization cross section is the result of two contributions, (i) the direct formation of SF3+ fragment ions via dissociative ionization of SF6 with a threshold energy of 22 eV and (ii) the Coulomb explosion of metastable SF42+ ions with a threshold energy of about 45.5 eV. A detailed analysis of the MIKE spectrum reveals an average kinetic energy release of about 5 eV in the Coulomb explosion of the SF42+ ions...
Dissociative photoionization dynamics of SF6 by ion imaging with synchrotron undulator radiation
Chemical Physics Letters, 1999
The technique of photofragment imaging, widely used in the study of neutral photochemistry, has been adapted to use on a vacuum ultraviolet undulator beamline at the advanced light source, affording a new approach to the study of dissociative ionization processes. The technique allows direct inversion of the raw data to yield angular and translational energy distributions for the product ions. The method is applied here to study the dissociative ionization of SF at photon energies 6 from 15 to 28 eV. The experiment allows for detailed characterization of the angular and translational energy distributions of the fragments, providing insight into the decay mechanisms of these excited ionic states. q 1999 Elsevier Science B.V. All rights reserved.
Journal of Physics B: Atomic, Molecular and Optical Physics, 2013
We investigate the multiphoton ionization and the subsequent fragmentation of SF 6 molecules with intense x-ray-free electron laser pulses at different photon energies. We observe highly charged molecular and atomic ions which were absent in previous experiments with conventional x-ray sources. The observation of fully stripped fluorine ions suggests sequential multiphoton ionization processes with intermediate 1s electron excitation. We measure the average momentum and kinetic energy of each fragment, the comparison of which implies many-body fragmentation pathways of the molecular ions. The observed non-monotonic dependence of the kinetic energy on the charge states of fluorine indicates the multiphoton ionization of 'isolated' atomic neutral fluorine or fluorine ions resultant from bond cleavages and also implies the fragmentation of highly charged molecular ions that are produced at a later time during a single pulse.
Fragmentation of valence electronic states of SF + 6 studied with synchrotron radiation
Journal of The Chemical Society, Faraday Transactions, 1991
Fragmentation of the seven valence electronic states of SF: has been studied in the range 440410 A by photoionisation mass spectrometry. The ion yield for SF; shows two thresholds at the adiabatic ionisation energy of the ground (z 2Tlg) and first two excited states (A 2T, and B 2T2,) of SF:. SF: shows a threshold at the third state (c 2E,) of SF:, SF,f shows two thresholds at the fourth and fith states (b2T2, and F2Tlu), and SF: turns on at the sixth state (F2Al,). Thus in all cases the appearance energy of a fragment ion occurs at the adiabatic ionisation potential of an electronic state of SF: , and not at the lower-lying thermochemical energy of the fragment ion. Kinetic energy releases have been measured in SF; , SF: and SF: at photon energies just above threshold for production of each ion. In the case of SF; a substantial fraction of the available energy is converted into translational energy of the fragments. The relative photoionisation yields of SF;, SF: and SF: are compared with values expected from the photoelectron branching ratios of electronic states of SF:. The latter results overestimate the yields of SF,f and SF: relative to SF;, and possible explanations are discussed.
Multielectron dissociative ionization of SF 6 in an intense femtosecond laser field
International Journal of Mass Spectrometry, 2004
The multielectron dissociative ionization of sulphur hexafluoride was investigated using 130 fs laser pulses at 810 nm wavelength. The pattern of the observed mass spectrum is explained based on the molecular structure symmetry and atomic ionization potentials. The kinetic energies of the atomic ions F + and F 2+ are consistent with a Coulomb explosion at a single critical internuclear distance. High precision angular distributions of atomic ions are obtained and the geometric alignment is responsible to the observed anisotropic angle distribution of energetic atomic ions.
The Journal of Chemical Physics, 1977
Ever since SF 6 has been observed to dissociate in an isotopically selective manner following multiphoton absorption from an intense infrared radiation field, 1,2 there has been considerable effort, both experimental and theoretical, to understand the mechanism responsible for this process. 3 Of particular importance is the identification of the initial photofragments. From mass spectrometric and infrared studies Kompa and co-workers 4 suggested that SF 6 initially decomposes into SF 4 + Fa, while from molecular beam studies Coggiola, Schulz, Lee, and Shen 5 concluded that dissociation proceeds via the lower energy path, SFs+ F. Further work by the same CO 2 LASER
3D Coincidence Imaging Disentangles Intense Field Double Detachment of SF6–
The efficient intense field double detachment of molecular anions observed in SF 6 − is studied by 3D coincidence imaging of the dissociation products. The dissociation anisotropy and kinetic energy release distributions are determined for the energetically lowest double detachment channel by virtue of disentangling the SF 5 + + F fragmentation products. The observed nearly isotropic dissociation with respect to the linear laser polarization and surprisingly high kinetic energy release events suggest that the dissociation occurs on a highly excited state. Rydberg (SF 6 + )* states composed of a highly repulsive dication core and a Rydberg electron are proposed to explain the observed kinetic energy release, accounting also for the efficient production of all possible cationic fragments at equivalent laser intensities.
Collisional decomposition of the sulfur hexaflouride anion (SF[sub 6][sup −])
The Journal of Chemical Physics, 2001
Insulating gas mixtures containing SF6 have been promoted to serve as replacements for pure SF6 in order to reduce SF6 atmospheric emission. It has been argued that some synergism may be achieved by choosing proper buffer gases in mixtures with SF6 such that the buffer gases efficiently slow down electrons into an energy range where the electron attachment cross section for SF6 is large. A complete understanding of the dielectric properties of SF6 mixtures obviously requires information about electron detachment from SF6" as collisional electron detachment may be the principal source of discharge initiation in SF6 mixtures. In this paper, we report total cross-section measurements for electron detachment and collision induced dissociation for collisions of SF6"with N2 for collision energies ranging up to a few hundred eV. The experimental results are analyzed using a two-step collision model where the unimolecular decomposition of collision ally excited SF6" ions is described in a statistical framework.
3D Coincidence Imaging Disentangles Intense Field Double Detachment of SF6–
Journal of Physical Chemistry A, 2015
The efficient intense field double detachment of molecular anions observed in SF 6 is studied by 3D coincidence imaging of the dissociation products. By disentangling specific product channels, the dissociation anisotropy and kinetic energy release distributions are determined for the SF 5 + + F fragmentation products, corresponding to the energetically lowest double detachment channel. The observed nearly isotropic dissociation with respect to the linear laser polarization and surprisingly high kinetic energy release events suggest that the dissociation occurs on a highly excited state. Rydberg (SF 6 +)* states composed of a highly repulsive dication core and a Rydberg electron are proposed to explain the observed kinetic energy release, accounting also for the efficient production of all possible cationic fragments at equivalent laser intensities.