Electron binding to valence and multipole states of molecules: Nitrobenzene, para- and meta-dinitrobenzenes

Nitrobenzene anions $(NB−)$ in both valence and dipole bound states are examined using laser (photodetachment) photoelectron and Rydberg electron transfer (RET) spectroscopies. Photoelectron spectroscopy of the valence $NB−$ anion yields a valence (adiabatic) electron affinity of $1.00±0.01 eV.$ The reaction rates for charge transfer between atoms of cesium and xenon in high Rydberg states [$Cs(ns,nd)$ and $Xe(nf )$] and NB exhibit a prominent peak in their n-dependencies consistent with the formation of a dipole bound anion having an electron affinity of 28 meV. Para-dinitrobenzene (pDNB) has a zero dipole moment and a large quadrupole moment. RET studies with pDNB show a complex n-dependence. The rate of formation of $pDNB−$ ions exhibits a broad peak at low n-values and a second very broad feature extending to large n-values. The peak at low n is tentatively attributed to charge exchange into a quadrupole bound state $(EAqb=25 meV).$ The absence of field-detachment for these ions suggests that if these are in a quadrupole bound state they are strongly coupled to the valence state. Meta-dinitrobenzene (mDNB) has a large dipole moment and a small quadrupole moment. The observation of a weak but narrow peak at a low n-value in the RET measurement is consistent with electron attachment into a primarily dipole bound state $(EAdb=68 meV)$ which is also strongly coupled to the valence state.