Knowledge Bank

High resolution electron transmission $spectroscopy1,2$(ETS) is employed to study the low-lying temporary anions pyridine, phosphabenzene, and arsabenzene, and the results compared with those of earlier studies of benzene. The $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}E2u(\pi \ast )$ ground state anion of benzene is split yielding $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A2$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1$ anions in the heterocompounds. The electron transmission spectra of pyridine indicates the existence of anions at 0.62 and 1.20 eV which have been assigned to the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A2$ anions, respectively. The transmission spectra of phosphabenzene and arsabenzene, on the other hand only display one temporary anion state below 3.0 eV which we attribute to the capture of an electron into the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}A2$ orbital of these compounds. We argue that the $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}B1$ anions are stable, and hence are not observable in an electron scattering experiment. A correlation diagram presenting both the electron affinities and ionization potentials of these compounds is presented. The positions in the energy levels of the P and As compounds are compared to those of pyridine and the shifts interpreted in terms of obital overlap and electronegativities.