The interaction of low-energy electron collisions with molecules may lead to temporary anions via resonant processes. While experimental measurements, e.g., electron transmission spectroscopy or dissociation electron attachment spectroscopy, are efficient to characterize the temporary anions, simulating the electron attachment is still very challenging. Here, we propose a methodology to calculate the resonance energies of the electron attachment using ab initio (TD)-DFT calculations together with two different basis sets: a large basis set with diffuse functions to compute the vertical electron affinity and a smaller one to calculate the excitation energy of the anion. To demonstrate the capabilities and the reliability of this computational approach, 53 resonance energies from 18 molecules are calculated and compared to experimental data.

Multi-Basis-Set (TD-)DFT Methods for Predicting Electron Attachment Energies.

In this contribution the dissociative electron attachment to metabolites found in aerobic organisms, namely oxaloacetic and citric acids, was studied both experimentally by means of a crossed-beam setup and theoretically through density functional theory calculations. Prominent negative ion resonances from both compounds are observed peaking below 0.5 eV resulting in intense formation of fragment anions associated with a decomposition of the carboxyl groups. In addition, resonances at higher energies (3–9 eV) are observed exclusively from the decomposition of the oxaloacetic acid. These fragments are generated with considerably smaller intensities. The striking findings of our calculations indicate the different mechanism by which the near 0 eV electron is trapped by the precursor molecule to form the transitory negative ion prior to dissociation. For the oxaloacetic acid, the transitory anion arises from the capture of the electron directly into some valence states, while, for the citric acid, dipole- or multipole-bound states mediate the transition into the valence states. What is also of high importance is that both compounds while undergoing DEA reactions generate highly reactive neutral species that can lead to severe cell damage in a biological environment.

/pdf/experimental-and-theoretical-studies-of-dissociative-3kvi7xi8tf.pdf

Experimental and Theoretical Studies of Dissociative Electron Attachment to Metabolites Oxaloacetic and Citric Acids

Metal acetylacetonate complexes have high potentiality in nanoscale fabrication processes (e.g., focus electron beam-induced deposition) thanks to the versatile character and ease of preparation compounds. In this work, we study and compare the physics and the physicochemistry induced by the interaction of low-energy (<10 eV) electrons with nickel(II) and cobalt(II) bis(acetylacetonate) complexes. The slow particles decompose the molecules via dissociative electron attachment. The nickel(II) and cobalt(II) bis(acetylacetonate) anions and the acetylacetonate negative fragments are the most dominant detected species. The experimental data are completed with density functional theory calculations to provide information on the electronic states of the molecules and the energetics for fragmentation. Finally, it is found that the interaction of low-energy electrons resulting in the decomposition of organometallic complexes in the gas phase is more efficient with the nickel(II) than with the cobalt(II) bis(acetylacetonate) complex. These results are found to be in a relative agreement with the surface experiments.

Fragmentation of Nickel(II) and Cobalt(II) Bis(acetylacetonate) Complexes Induced by Slow (<10 eV) Electrons

Nowadays, organometallic complexes receive particular attention because of their use in the design of pure nanoscale metal structures. In the present work, we present results obtained from a series of studies on the degradation of metal(II) bis(acetylacetonate)s induced by low-energy electrons. These slow particles induce the formation of the acetylacetonate anion, [acac]-, and the parent anion as the most dominant species at incident electron energies near 0 eV. They also fragment the organometallic compounds via various competitive reaction channels that occur at higher energies via dissociative electron attachment. The reported data may contribute to a better understanding of the physical chemistry underlying the electron-molecule interactions, which is crucial for potential applications of these molecular systems in the deposition of nanoscale structures. 

pdf/fragmentation-of-metal-ii-bis-acetylacetonate-complexes-1fm1o8r6xs.pdf

Fragmentation of metal(II) bis(acetylacetonate) complexes induced by slow electrons

Formaldehyde (FA) is a highly toxic substance present in many matrices, including freshwater as well as found in natural mechanisms such as rainfall and combustion of organic matter. Consumption of water contaminated with high levels of FA can cause severe short-term or long-term health problems. Due to these health risks, procedures are necessary to determine and quantify FA in aqua sources This paper reports on a study of fluorimetric determination of FA using a nickel(2 + )-diketonate coordination compound immobilized as a solid precursor. The compound was characterized by electronic absorption, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), thermogravimetry (TG), optical microscopy (OM), and scanner electron microscopy (SEM). The methodology was based on the reaction of the synthesized compound with an ammoniacal buffer generating a selective reagent for formaldehyde: fluoral-P. The product of the reaction generates 3,5-diacetyl-1,4-dihydrolutidine (DDL), which is responsible for the fluorescence of the system. Several parameters such as temperature, duration of heating time, and dilution effect with the best effects were studied to carry out FA determination. Under the optimum experimental conditions, a linear response ranging from 1.0 to 10.0 mg/L FA (R = 0.997 and n = 10), and a detection (3σ criterion) and quantification (10 σ criterion) limit estimated at 0.129 and 0.389 mg/L, respectively were achieved. The FA analysis was able to be conducted in 05 min with a relative standard deviation estimated at 1.10 %. 

Fluorimetric determination of aqueous formaldehyde employing heating and ultrasound-assisted approach through its derivatization with a ß-diketone-nickel(2+) complex immobilized in a PMMA flow cell.

Dissociative electron attachment is a mechanism found in a large area of research and modern applications. This process is initiated by a resonant capture of a scattered electron to form a transitory anion via the shape or the core-excited resonance that usually lies at energies above the former (i.e., >3 eV). By studying experimentally and theoretically the interaction of nickel(II) (bis)acetylacetonate, Ni(II)(acac)2, with low energy electrons, we show that core-excited resonances are responsible for the molecular dissociation at unusually low electron energies, i.e., below 3 eV. These findings may contribute to a better description of the collision of low energy electrons with large molecular systems.

Core-excited resonances initiated by unusually low energy electrons observed in dissociative electron attachment to Ni(II) (bis)acetylacetonate.

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Core-excited resonances initiated by unusually low energy electrons observed in dissociative electron attachment to Ni(II) (bis)acetylacetonate.