Dipole-bound anions of carbonyl, nitrile, and sulfoxide containing molecules

Dipole-bound anions of 27 molecules containing either a carbonyl, nitrile, or sulfoxide group were studied using Rydberg electron transfer (RET) reactions with rubidium atoms excited to $ns 2S$ and $nd 2D$ excited states. The electron affinity of each molecule was obtained from the Rydberg state, $nmax*,$ that gave the largest negative ion yield using the empirical relationship electron affinity=$23/nmax*2.8 eV$ as well as from fitting the charge exchange profile to a theoretical curve crossing model. Electron affinities for the low dipole moment molecules (carbonyls) were also deduced from measurements of the electric field required to detach the electron from the anion. Calculations of the electron affinities for some of the nitriles at the coupled-cluster level of theory were performed. The dependencies of the electron affinity upon dipole moment, polarizability, dispersion interaction, conformation, and geometry of the molecules were investigated. It was found that a higher dipole moment generally results in a higher electron affinity. However, for molecules with similar dipole moments, other factors such as polarizability and the dispersion interaction play an important role. The effect of collision velocity on the creation of these anions is also studied through the use of different carrier gases $(H2,$ He, Ne, Ar, Kr, Xe) in the nozzle jet expansion. Competition between RET and collisional detachment is observed and discussed qualitatively.