Ion-pair dissociation dynamics in electron collision with carbon dioxide probed by velocity slice imaging (original) (raw)
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Fragmentation dynamics in dissociative electron attachment to CO probed by velocity slice imaging
Physical chemistry chemical physics : PCCP, 2015
Complete dissociation dynamics in electron attachment to carbon monoxide (CO) have been studied using the newly developed velocity slice imaging (VSI) technique. Both kinetic energy and angular distributions of O(-) ions formed by dissociative electron attachment (DEA) to CO molecules have been measured for 9, 9.5, 10, 10.5, 11, and 11.5 eV incident electron energies around the resonance. Detailed observations conclusively show that two separate DEA reactions lead to the formation of O(-) ions in the ground (2)P state along with the neutral C atoms in the ground (3)P state and the first excited (1)D state, respectively. Within the axial recoil approximation and involving four partial waves, our angular distribution results clearly indicate that the two reactions leading to O(-) formation proceed through the specific resonant state(s). For the first process, more than one intermediate state is involved. On the other hand, for the second process, only one state is involved. The observ...
Dissociation dynamics in the dissociative electron attachment to carbon dioxide
Physical Review A, 2015
Dissociative electron attachment (DEA) to gas phase CO 2 has been probed using a velocity slice imaging technique. DEA to CO 2 produces only an O − ionic fragment and shows two major resonances located at 4.4 and 8.2 eV, respectively. The kinetic energy and angular distribution of the O − ions are measured around the second resonance with higher efficiency and sensitivity that provide details of the DEA dynamics. The kinetic energy distributions are in good agreement with the previous reports. However, the distinct angular distributions show substantial difference from the two recent studies within the limited electron energies. Our angular distribution results show two negative ion resonant states are involved in the underlying DEA process at the entire electron energies over the second resonance. We discussed the recent conflicting findings in the angular distribution results. The forward-backward asymmetry observed in the angular distributions is explained due to the interference effect of different partial waves associated with the attaching electron.
COLTRIMS Imaging of Molecular Fragmentation Dynamics of CO Molecules Induced by Slow He 2 + Ions
2015
We study the multiple ionization and fragmentation of CO in collisions with slow He ions. Correlated measurements of all fragment ions and the projectile final charge state were performed using our coincidence COLTRIMS imaging technique coupled to projectile charge state separation. Complete fragmentations of CO, following double electron capture, into C+O with a total charge of 4 were investigated. The kinetic energy release (KER) distributions and their dependence on the molecule-axis orientation and on the projectile ion velocity were studied. A strong dependence of the kinetic energy release on the velocity of the He ions is observed. Furthermore, we find that the KER values are shifted toward higher energies when the molecule is aligned with the beam direction.
Ion kinetic energy spectroscopy of the doubly charged ion of carbon monoxide
The Journal of Chemical Physics, 1984
Spontaneous and collision-induced dissociation processes of C02+ ions, formed by electron impact, have been studied in a double-focusing mass spectrometer using techniques of ion kinetic energy spectroscopy. The predissociation process, responsible for unimolecular dissociation of C02+ on the microsecond time scale, is almost certainly electronically adiabatic tunneling through a potential barrier, though predissociation via electronic curve crossing cannot be entirely ruled out. Semiempirical potential curves for states ofC0 2 + were revised in order to better accommodate all of the available data, including Auger spectra, appearance energies, and kinetic energy release. Collision induced dissociation processes with Ar, N 2 , and H2 proceed via charge exchange, and involve predissociation of the D 2II state by the C 2..1 state ofCO+. When He is used as collision gas, the dissociation processes involving charge exchange are different, and require an energetic contribution from the relative kinetic energy (kinetic energy loss). In addition, He is quite different in inducing dissociation of C0 2 + without prior charge exchange, from states ofC02+ up to 13 eV above the dissociation limit.
Ion-induced molecular fragmentation: beyond the Coulomb explosion picture
Journal of Physics B: Atomic, Molecular and Optical Physics, 2000
The fragmentation of the CO molecule by O 7+ ion impact is investigated in two different energy regimes by fragment ion momentum spectroscopy. The improved resolution of the present kinetic energy release measurement together with application of a time-dependent wavepacket dynamics method used in conjunction with new high-level computations of a large number of dication potential energy curves enables one to unambiguously assign each line to an excited state of the transient molecular dication produced during the collision. This is the first direct experimental evidence of the limitations of the Coulomb explosion model to reproduce the molecular fragmentation dynamics induced by ion impact. Electron removal due to a capture process is shown to transfer less excitation to the target than direct ionization. At low collision velocity, the three-body interaction between the projectile and the two fragments is also clearly highlighted.
Physical Review A
In this work, we experimentally study the angle-dependent single ionization of carbon dioxide (CO 2) by linearly and circularly polarized pulses. The angle dependence of the ionization probability by linearly polarized pulses extracted from time-domain measurements on an impulsively excited rotational wave packet is compared with data obtained from a direct angle-scan measurement. The results from the measurement with linear and circular polarization are consistent with the adiabatic ionization approximation. We extend the time-domain method to extract the dependence of the asymptotic momentum distribution of fragment ions on the orientation of the molecular axis, and apply it to investigate dissociative double ionization of CO 2. We show that such measurements can directly test the validity of the axial recoil approximation.
Dissociative multiple ionization of carbon dioxide dimers in intense femtosecond laser fields
Physical Review A
Molecular dimers have attracted much attention in the study of molecular structure and dynamics due to their complex interactions involving both weak van der Waals and strong covalent bonds. We investigate the dissociative ionization of carbon dioxide dimers exposed to intense femtosecond laser fields. The angular distributions of ionic fragments of the breakup channels (CO 2) 2 2+ → CO 2 + + CO 2 + and (CO 2) 2 3+ → CO 2 2+ + CO 2 + strongly depend on the laser intensity. Simulations based on time-dependent density-functional theory reproduce the experimental observations qualitatively and show that the angular distribution of fragments is determined by the angle-dependent orbital ionization probability and the relative contributions of different orbitals, both of which are intensity sensitive. By comparing the ionization of the dimer with CO 2 monomer, we find that the weak van der Waals bond and molecular geometry in the dimer play considerable roles. This work extends significantly earlier studies of simple linear covalent bond molecules.
The Journal of Chemical Physics
The fragmentation of the doubly-charged carbon dioxide molecule is studied after photoexcitation to the C 1s(1)2π(u) and O 1s(1)2π(u) states using a multicoincidence ion-imaging technique. The bent component of the Renner-Teller split states populated in the 1s→ π* resonant excitation at both the carbon and oxygen 1s ionization edges opens pathways to potential surfaces in highly bent geometries in the dication. Evidence for a complete deformation of the molecule is found in the coincident detection of C(+) and O(2)(+) ions. The distinct alignment of this fragmentation channel indicates rapid deformation and subsequent fragmentation. Investigation of the complete atomization dynamics in the dication leading to asymmetric charge separation shows that the primary dissociation mechanisms, sequential, concerted, and asynchronous concerted, are correlated to specific fragment kinetic energies. The study shows that the bond angle in fragmentation can extend below 20°.
Triple-differential cross sections for single ionization of CO2 by 100 eV electron impact
Journal of Physics B: Atomic, Molecular and Optical Physics, 2018
We present a combined experimental and theoretical study for electron-impact ionization of carbon dioxide (CO 2) for the projectile energy E 0 =100 eV. Experimental triple-differential cross sections (TDCS) are obtained using a multi-particle momentum spectrometer (reaction microscope). For projectile scattering angles between −5°and −20°a large part of the full solid angle is covered for the slow ejected electron with energies between 5 and 15 eV. The experimental data are measured for the ionization of the three outer valence molecular orbitals 1π g , 1π u , and 3σ u which lead to a non-dissociating CO 2 + ion. The measured TDCS summed over all three orbitals are internormalized across the scattering angles and ejected electron energies. They are compared to the theoretical results from the multi-center distorted wave (MCDW) approximation, and from the MCDW-WM approximation which includes post-collision interaction using the Ward-Macek factor (WM). Reasonable good agreement is found between the experiment and the MCDW-WM calculations for the angular dependence and the relative magnitude of the cross sections in the coplanar plane, while for the perpendicular and full perpendicular planes larger discrepancies exist. Since post-collision interaction is not considered the MCDW method shows strong discrepancies with experiment for small mutual angles of the two outgoing electrons in the final state.electron impact, ionization, kinematically complete (e, 2e) experiment, CO 2 , MCDW