Temporary anion states of three herbicide families.

Electron scattering studies are used to locate the energies of temporary negative ion states of three chloro-substituted molecular families of herbicidal importance: salicylic and phenoxyacetic acids and acetamides. The correlation between these energies and the computed virtual orbital energies of the compounds is examined and used to put the latter on an absolute energy scale. Such scaling of orbital energies permits the anion states of other members of these families, for which experimental data may not be available, to be estimated from the calculated orbital energies.

On the treatment of LUMO energies for their use as descriptors.

Calculated energies of lowest unoccupied molecular orbitals (LUMOs) are frequently employed as descriptors in studies of quantitative structure-activity relationships and linear free energy relationships involving electron transfer. However, the quantum chemical programs with which these are carried out, whether Hartree-Fock or density functional theory, do not treat orbitals of different character, for example, C=C π(∗) and C-Cl σ(∗), consistently, nor is there consistency among different families of compounds. These problems can be ameliorated with the use of the experimental equivalent of the LUMO energy, the vertical attachment energy (VAE), or by shifting and scaling LUMO energies to a training set of available VAEs in similar compounds.

Electron attachment to dye-sensitized solar cell components: cyanoacetic acid.

The energies of electron attachment associated with temporary occupation of the lower-lying virtual orbitals of cyanoacetic acid (CAA), proposed as a possible component of dye-sensitized solar cells, and its derivative methyl cyanoacetate (MCA) are measured in the gas phase with electron transmission spectroscopy (ETS). The corresponding orbital energies of the neutral molecule, supplied by B3LYP/6-31G(d) calculations and scaled using an empirically calibrated linear equation, are compared with the experimental vertical attachment energies (VAEs). The vertical and adiabatic electron affinities are also evaluated at the B3LYP/6-31+G(d) level as the anion/neutral total energy difference.

Dissociative electron attachment in nonplanar chlorocarbons with pi*/sigma*-coupled molecular orbitals.

Total absolute cross sections for the dissociative electron attachment (DEA) process are reported for a series of nonplanar ethylenic and phenylic compounds monosubstituted with (CH(2))(n)Cl groups, where n=1-4. Coupling between the local pi* molecular orbitals provided by the unsaturated moieties and the sigma* (C-Cl) orbital is thus examined as a function of the separation of these groups. In particular, the coupling is viewed from the perspective of the interacting temporary negative ions formed by short lived occupation of these orbitals and their decay into the DEA channel.

Electron attachment to trans-azobenzene.

The temporary anion states of gas-phase trans-azobenzene are characterised by means of electron transmission spectroscopy (ETS) in the 0-6 eV range. The measured energies of vertical electron attachment are compared with the energies of the pi* virtual orbitals of the neutral molecule supplied by HF (at MP2 optimized geometries) and B3LYP calculations. The calculated energies, scaled with empirical equations, reproduce quantitatively the energies of the corresponding spectral features and predict a positive vertical electron affinity of 0.