Resonances in nitrobenzene probed by the electron attachment to neutral and by the photodetachment from anion

We probe resonances (transient anions) in nitrobenzene with the focus on the electron emission from these. Experimentally, we populate resonances in two ways: either by the impact of free electrons on the neutral molecule or by the photoexcitation of the bound molecular anion. These two excitation means lead to transient anions in different initial geometries. In both cases, the anions decay by electron emission and we record the electron spectra. Several types of emission are recognized, differing by the way in which the resulting molecule is vibrationally excited. In the excitation of specific vibrational modes, distinctly different modes are visible in electron collision and photodetachment experiments. The unspecific vibrational excitation, which leads to the emission of thermal electrons following the internal vibrational redistribution, shows similar features in both experiments. A model for the thermal emission based on a detailed balance principle agrees with the experimental findings very well. Finally, a similar behavior in the two experiments is also observed for a third type of electron emission, the vibrational autodetachment, which yields electrons with constant final energies over a broad range of excitation energies. The entrance channels for the vibrational autodetachment are examined in detail, and they point to a new mechanism involving a reverse valence to non-valence internal conversion

Study of electron beam induced ion-pair dissociation dynamics of O

The ion-pair dissociation (IPD) of molecular oxygen due to 21–35 eV energy electron collision has been studied using the time sliced velocity map imaging technique. The threshold of the process and the kinetic energy and angular distribution of the fragment negative ions are measured. The IPD is found to be occurring due to pre-dissociation of a Rydberg state via ion-pair state for lower incident electron energies as well as from direct excitation to the ion-pair states for higher primary beam energy. The location and symmetry of the excited states are determined from the kinetic energy and angular distribution data respectively

Dissociative electron attachment to methyl isocyanide

We experimentally probed the dissociation of methyl isocyanide, CH$$_3$$NC, via low-energy electron attachment. We have measured the absolute dissociative electron attachment (DEA) cross section for each of the produced ions as a function of incident electron energy. We were able to observe the CH$$_2^-$$, CH$$_3^-$$, CN$$^-$$, CNC$$^-$$, CHNC$$^-$$ and CH$$_2$$NC$$^-$$ anionic fragments as DEA products. Our experimental results are consistent with a previous report, and in addition, we observed the CH$$_2^-$$ anion for the first time. To support these experimental results, we also have performed density functional theory (DFT) calculation at the B3LYP/aug-cc-pVTZ level of theory to find out which reaction channel(s) lead to the formation of a given anion

Dissociative attachment of low-energy electrons to acetonitrile

We experimentally probed the low-energy electron-induced dissociation of acetonitrile and acetonitrile-$$\hbox {d}_3$$ and performed density functional theory calculations to support the experimental results. The previous studies on electron attachment to acetonitrile presented a number of contradictory findings, which we aimed to resolve in the present study. We observed the formation of $$\hbox {H}^-$$, $$\hbox {CH}_2^-$$, $$\hbox {CH}_3^-$$, $$\hbox {CN}^-$$, $$\hbox {CCN}^-$$, $$\hbox {CHCN}^-$$ and $$\hbox {CH}_2 \hbox {CN}^-$$ anions and the corresponding deuterated fragments for acetonitrile-$$\hbox {d}_3$$ by dissociative electron attachment, and measured ion yields curves of each fragment. We saw no evidence for associative electron attachment to form the parent ion in these measurements. We also have measured the kinetic energy and angular distribution of selected fragments using a velocity map imaging (VMI) spectrometer

Dissociative electron attachment to carbon tetrachloride probed by velocity map imaging

Bond-breaking in CCl4via dissociative electron attachment (DEA) has been studied using a velocity map imaging (VMI) spectrometer. A number of effects related to the dissociation dynamics have been revealed. The near-zero eV s-wave electron attachment, which leads to the production of Cl- anions, is accompanied by a very efficient intramolecular vibrational redistribution. This is manifested by a small fraction of the excess energy being released in the form of the fragments' translation energy. A similar effect is observed for higher-lying electronic resonances with one exception: the resonance centered around 6.2 eV leads to the production of fast Cl2- fragments and their angular distribution is forward peaking. This behavior could not be explained with a single-electronic-state model in the axial recoil approximation and is most probably caused by bending dynamics initiated by a Jahn-Teller distortion of the transient anion. The CCl2- fragment has a reverse backward-peaking angular distribution, suggesting the presence of a long-distance electron hopping mechanism between the fragments

Spectroscopic signatures of states in the continuum characterized by a joint experimental and theoretical study of pyrrole

We report a combined experimental and theoretical investigation of electron-molecule interactions using pyrrole as a model system. Experimental two-dimensional electron energy loss spectra (EELS) encode information about vibrational states of the molecule as well as position and structure of electronic resonances. The calculations using non-Hermitian extensions of equation-of-motion coupled-cluster theory facilitate the assignment of all major EELS features. We confirm the two previously described π* resonances at about 2.5 and 3.5 eV (the calculations place these two states at 2.92 and 3.53 eV vertically and 2.63 and 3.27 adiabatically). The calculations also predict a low-lying resonance at 0.46 eV, which has a mixed character---of a dipole-bound state and σ* type. This resonance becomes stabilized at one quanta of the NH excitation, giving rise to the sharp feature at 0.9 eV in the corresponding EELS. Calculations of Franck-Condon factors explain the observed variations in the vibrational excitation patterns. The ability of theory to describe EELS provides concrete illustration of the utility of non-Hermitian quantum chemistry, which extends such important concepts as potential energy surfaces and molecular orbitals to states embedded in the continuum

Decomposition of Iron Pentacarbonyl Induced by Singly and Multiply Charged Ions and Implications for Focused Ion Beam-Induced Deposition

International audienceFocused ion beams are becoming important tools in nanofabrication.The underlying physical processes in the substrate were already explored for severalprojectile ions. However, studies of ion interaction with precursor molecules forbeam-assisted deposition are almost nonexistent. Here, we explore the interaction ofvarious projectile ions with iron pentacarbonyl. We report fragmentation patterns ofisolated gas-phase iron pentacarbonyl after interaction with 4He+ at a collisionenergy 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 coverinteraction regimes ranging from collisions dominated by nuclear stopping throughcollisions dominated by electronic stopping to soft resonant electron-captureinteractions. We report a surprising efficiency of Ne+ in the Fe(CO)5decomposition. The interaction with multiply charged ions results in a highercontent of parent ions and slow metastable fragmentation due to the electroncaptureprocess. 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