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 exami ned using laser (photodetachment) photoelectron and Rydberg electron transf er (RET) spectroscopies. Photoelectron spectroscopy of the valence NB- anio n yields a valence (adiabatic) electron affinity of 1.00 +/- 0.01 eV. The r eaction 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 zer o 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 bro ad 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 in to a quadrupole bound state (EA(qb)=25 meV). The absence of field-detachmen t for these ions suggests that if these are in a quadrupole bound state the y 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 (EA(db)=68 meV ) which is also strongly coupled to the valence state. (C) 1999 American In stitute of Physics. [S0021-9606(99)30534-1].