Temperature Dependence of the Dissociative Electron Attachment to 2-Thiothymine

Production of Nitrogen Dioxide, NO2-, Anion from Dissociative Electron Attachment to Nitromethane below 1 eV and Its Temperature Dependence: Direct vs Dipole Bound Mediated Processes

Reaction induced by slow electrons is implicated in a large field of research and applications. Below 3-4 eV, dissociative electron attachment efficiently fragments molecules via (1) shape resonance or (2) mediated by the formation of a dipole bound anion. While the temperature dependence of process 1 is well-known, that of 2 is not clearly established. Nitromethane is the prototypical molecule for which the electron attachment leads to the formation of both a dipole bound and a covalent anion. We provide here a comprehensive study of the fragmentation of nitromethane by <1 eV electron and the unusual temperature effects attributed principally to process 2.

Electron attachment to microhydrated 4-nitro- and 4-bromo-thiophenol

We investigate the effect of microhydration on electron attachment to thiophenols with halogen (Br) and nitro (NO₂) functional groups in the para position. We focus on the formation of anions upon the attachment of low-energy electrons with energies below 8 eV to heterogeneous clusters of the thiophenols with water. For nitro-thiophenol (NTP), the primary reaction channel observed is the associative electron attachment, irrespective of the microhydration. On the other hand, bromothiophenol (BTP) fragments significantly upon the electron attachment, producing Br^- and (BTP-H)^- anions. Microhydration suppresses fragmentation of both molecules, however in bromothiophenol, the Br^- channel remains intense and Br(H₂O)_n^- hydrated fragment clusters are observed. The results are supported by the reaction energetics obtained from ab initio calculations. Different dissociation dynamics of NTP and BTP can be related to different products of their plasmon induced reactions on Au nanoparticles. Computational modeling of the simplified BTP(H₂O) system indicates that the electron attachment products reflect the structure of neutral precursor clusters - the anion dissociation dynamics is controlled by the hydration site.

Radiation Induced One-Electron Oxidation of 2-Thiouracil in Aqueous Solutions

Oxidative damage to 2-thiouracil (2-TU) by hydroxyl (•OH) and azide (●N3) radicals produces various primary reactive intermediates. Their optical absorption spectra and kinetic characteristics were studied by pulse radiolysis with UV-vis spectrophotometric and conductivity detection and by time-dependent density functional theory (TD-DFT) method. The transient absorption spectra recorded in the reactions of •OH with 2-TU depend on the concentration of 2-TU, however, only slightly on pH. At low concentrations, they are characterized by a broad absorption band with a weakly pronounced maxima located at λ = 325, 340 and 385 nm, whereas for high concentrations, they are dominated by an absorption band with λmax ≈ 425 nm. Based on calculations using TD-DFT method, the transient absorption spectra at low concentration of 2-TU were assigned to the ●OH-adducts to the double bond at C5 and C6 carbon atoms (3●, 4●) and 2c-3e bonded ●OH adduct to sulfur atom (1…●OH) and at high concentration of 2-TU also to the dimeric 2c-3e S-S-bonded radical in neutral form (2●). The dimeric radical (2●) is formed in the reaction of thiyl-type radical (6●) with 2-TU and both radicals are in an equilibrium with Keq = 4.2 × 103 M-1. Similar equilibrium (with Keq = 4.3 × 103 M-1) was found for pH above the pKa of 2-TU which involves admittedly the same radical (6●) but with the dimeric 2c-3e S-S bonded radical in anionic form (2●-). In turn, ●N3-induced oxidation of 2-TU occurs via radical cation with maximum spin location on the sulfur atom which subsequently undergoes deprotonation at N1 atom leading again to thiyl-type radical (6●). This radical is a direct precursor of dimeric radical (2●).

Temperature dependence of dissociative electron attachment to bromo-chlorotoluene isomers: Competition between detachment of Cl- and Br. J Chem Phys 2018;148:074301. [PMID: 29471640 DOI: 10.1063/1.5013606]

Dissociative electron attachment to three isomers of bromo-chlorotoluene was investigated in the electron energy range from 0 to 2 eV for gas temperatures in the range of 392-520 K using a crossed electron-molecular beam apparatus with a temperature regulated effusive molecular beam source. For all three molecules, both Cl^- and Br^- are formed. The ion yields of both halogenides show a pronounced temperature effect. In the case of Cl^- and Br^-, the influence of the gas temperature can be observed at the threshold peak close to 0 eV. The population of molecules that have some of their out-of-plane modes excited varies strongly in the temperature range investigated, indicating that such vibrations might play a role in the energy transfer towards bond breaking. Potential energy curves for the abstraction of Cl^- and Br^- were calculated and extrapolated into the metastable domain. The barriers in the diabatic curves approximated in this way agree well with the ones derived from the temperature dependence observed in the experiments.

Interaction of gas phase copper(ii) acetylacetonate with slow electrons

Understanding the fundamental processes underlying the interaction of organometallic compounds with low energy electrons is desirable for optimizing methodologies for nanoscale applications.