Electronic resonances commonly decay via internal conversion to vibrationally hot anions and subsequent statistical electron emission. We observed vibrational structure in such an emission from the nitrobenzene anion, in both the 2D electron energy loss and 2D photoelectron spectroscopy of the neutral and anion, respectively. The emission peaks could be correlated with calculated nonadiabatic coupling elements for vibrational modes to the electronic continuum from a nonvalence dipole-bound state. This autodetachment mechanism via a dipole-bound state is likely to be a common feature in both electron and photoelectron spectroscopies.
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 observed forward-backward asymmetry is explained in terms of the interference between the different partial waves that are involved in the processes.
We probe the transient anion states (resonances) in the dielectric gas C4F7N by the electron energy loss spectroscopy and the dissociative electron attachment spectroscopy. The vibrationally inelastic electron scattering leads to two excitation types. The first is the excitation of specific vibrational modes that are assigned with the help of an infrared spectrum of this molecule and quantum chemistry calculations. In the second type of vibrational excitation, the excess energy is randomized via internal vibrational redistribution in the temporary anion, and the electrons are emitted statistically. The electron attachment proceeds in three different regimes. The first is the formation of the parent C4F7N− anion at energies close to 0 eV. The second is a statistical evaporation of the F-atom, leading to the defluorinated anion C4F6N−. Finally, the third is dissociative electron attachment proceeding via the formation of several resonances and leading to a number of fragments. The present data explain the puzzling recent results of the pulsed-Townsend experiments with this gas.
Focused ion beams
are becoming important tools in nanofabrication.
The underlying physical processes in the substrate were already explored
for several projectile ions. However, studies of ion interaction with
precursor molecules for beam-assisted deposition are almost nonexistent.
Here, we explore the interaction of various projectile ions with iron
pentacarbonyl. We report fragmentation patterns of isolated gas-phase
iron pentacarbonyl after interaction with 4He+ at a collision energy of 16 keV, 4He2+ at
16 keV, 20Ne+ at 6 keV, 20Ne4+ at 40 keV, 40Ar+ at 3 keV, 40Ar3+ at 21 keV, 84Kr3+ at 12 keV,
and 84Kr17+ at 255 keV. These projectiles cover
interaction regimes ranging from collisions dominated by nuclear stopping
through collisions dominated by electronic stopping to soft resonant
electron-capture interactions. We report a surprising efficiency of
Ne+ in the Fe(CO)5 decomposition. The interaction
with multiply charged ions results in a higher content of parent ions
and slow metastable fragmentation due to the electron-capture process.
The release of CO groups during the decomposition process seems to
take off a significant amount of energy. The fragmentation mechanism
may be described as Fe being trapped within a CO cluster.
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