RESONANCE ELECTRON-CAPTURE RATE CONSTANTS FOR SUBSTITUTED NITROBENZENES

We report here a new method for the determination of electron capture (EC) rate constants that utilizes a pulsed electron beam mass spectrom eter. The method is first tested by measurements of the known dissocia tive electron capture rate constants for several halogenated methanes that have been extensively studied by other techniques. The resonance electron capture (REC) rate constants of nitrobenzene (NB) and 23 subs tituted nitrobenzenes (SNB's) are then determined for the first time a t 125 degrees C in 10 Torr of methane buffer gas. The SNB's studied he re include several sets of closely related structural isomers whose el ectron affinities (EA's) have been previously determined. It is shown that the REC rate constants of these compounds bear little systematic relationship with the EA's of these compounds. The REC rate constants of the SNB's are also compared with other previously reported characte ristics associated with the negative ionization of these compounds, in cluding their entropies of negative ionization, the lifetimes against autodetachment of their initially formed molecular anions, and the rat es of autodetachment from electronically excited states of their molec ular anions.