A relation between energies of the short-lived negative ion states and energies of unfilled molecular orbitals for a series of bromoalkanes

A series of bromoalkanes was investigated by means of electron transmission spectroscopy in the gas phase. Experimental values of vertical electron affinities associated with occupation of the LUMO by an incoming electron were assigned using ab initio quantum chemical calculations. The predicted vertical electron affinity values differ from measured ones by at most ±0.2 eV

Molecular anion formation in 9,10-anthraquinone: dependence of the electron detachment rate on temperature and incident electron energy.

Attachment of low-energy electrons to gas phase 9,10-anthraquinone (AQ) was observed with Electron Transmission Spectroscopy (ETS), and interpreted with the support of quantum chemical calculations. The ET spectrum displays three shape resonances at 0.45, 0.7 and 2.2 eV, associated with temporary electron capture into empty * molecular orbitals of AQ, the first two anion states being stable. According to TD-B3LYP calculations, the first -* core-excited resonance lies at about 1.8 eV, although no experimental evidence for this anion state was found. The long-lived parent molecular anion [AQ]\u2013 was observed by means of Electron Attachment Spectroscopy (EAS) using two different mass spectrometers and also by measuring the total anion current at the collision chamber walls. The molecular anion current shows maxima at zero energy, around 0.6 eV and at 1.8 eV. Association of these maxima with the corresponding resonant anion states is discussed. The experimentally measured electron detachment times from [AQ]\u2013 as a function of the incident electron energy and the temperature of the target molecule show a pronounced change of slope around 1.5 eV, regardless of the temperature. This unexpected behavior can be qualitatively reproduced within the framework of a multi-exponential approach which describes the electron detachment event in terms of a redistribution of the anion excess energy, regardless of the initial mechanism of temporary anion formation

Electron structure and geometry of tiophene derivatives

Photoelectron spectra of three tiophene derivatives have been measured. Quantum chemical calculations (the MNDO method) of electron structure of molecules under investigation have been carried out. The interpretation of ionization energies in the region 7 - 11 eV has been made with the help of calculations of torsion vibrations of substituents. It is shown that in the case of 3-SMe-Thiophene and 3-SBut-Thiophene contributions of plane and out-of-plane substituent conformations are approximately equal. Molecules of 3-SH-Tiophene have predominantly plane conformation

Thermal electron capture by some chlorobromopropanes

Thermal electron attachment rate constants for CH2ClCHBrCH3 and CH2ClCH2CH2Br have been measured using electron swarm method. Corresponding rate constants are equal to $3.5\times10^{-10}$ and $2.5\times10^{-10}$ cm3 molec-1 s-1, respectively. Parallely, negative ion mass spectra of these compounds as well as CH2FCH2Br, CH2ClCH2Br, CH2BrCH2Br and CF3CHClBr has been measured with negative ion mass spectrometry method. The rate constants have been compared with the negative ion mass spectra

On likely linkage between dissociative electron attachment and biological effects produced by xenobiotics

A possible correlation between electron acceptor properties, in particular, dissociative electron attachment (DEA) and biological activity for a series of xenobiotic species (organic pollutants, polyphenolic antioxidants, and ascorbic acid) is reported. Formation and decay of temporary negative ions (TNIs) are studied using electron transmission and DEA spectroscopies. Experimental findings are assigned with the support of density functional theory calculations and are discussed in connection with the effects produced by these compounds in living cells. The basic ideas of the present study are derived from the work published in the earlier 60th of the XX century by A. Szent-Györgyi [1,2] and J. Lovelock [3]. Likely sources of electrons able to interact with xenobiotic molecules to form TNIs under cellular conditions are tentatively associated with mitochondria and cytochrome P450 enzymes. The formed TNIs are supposed to decay via the DEA mechanism producing negatively charged and neutral fragments, in analogy with those observed by DEA spectroscopy under gas-phase conditions. Electrochemical studies of reductive dehalogenation [4] and dehydrogenation [5] in solution demonstrate that TNIs can dissociate in condensed environment instead of dissipating their excess energy. Preliminary conclusions about a correlation between DEA and biochemical processes are summarized