Rydberg electron attachment to gas-phase isolated uracil molecules and mixed uracil-argon clusters is examined in a crossing beam experiment. By means of reproducible uracil beam conditions, it is possible to control the electron-binding process, which is strongly influenced by solvation. Attachment followed by evaporation of a single argon atom is already sufficient to switch from dipole-bound to valence monomer uracil anions, as demonstrated by field-detachment measurements. The existence of both types of anions is in good agreement with two separate previous theoretical predictions. A DFT calculation of the valence adiabatic electron affinity of uracil provides a small but positive value of 70 meV, close to the measured value of the dipole-bound electron affinity.

No abstract

Low-energy photoelectron imaging spectroscopy of nitromethane anions: Electron affinity, vibrational features, anisotropies, and the dipole-bound state J. Chem. Phys. 130, 074307 (2009); 10.1063/1.3076892Effect of excess electron and one water molecule on relative stability of the canonical and zwitterionic tautomers of glycine Nitrobenzene anions (NB Ϫ ) in both valence and dipole bound states are examined using laser ͑photodetachment͒ photoelectron and Rydberg electron transfer ͑RET͒ spectroscopies. Photoelectron spectroscopy of the valence NB Ϫ anion yields a valence ͑adiabatic͒ electron affinity of 1.00Ϯ0.01 eV. The reaction rates for charge transfer between atoms of cesium and xenon in high Rydberg states ͓Cs(ns,nd) and Xe(n f )͔ 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 ͑pDNB͒ 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 Ϫ 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 (EA qb ϭ25 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 ͑mDNB͒ 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 ϭ68 meV) which is also strongly coupled to the valence state.

The influence of N-methylation on the dipole-bound electron affinities of pyrimidine nucleic acid bases, uracil and thymine, has been investigated theoretically using ab initio quantum mechanical calculations, and experimentally using Rydberg electron transfer spectroscopy. Both experiment and theory are consistent in showing that replacement of hydrogen atoms by methyl groups reduces electron affinities corresponding to formation of dipole-bound anions of these systems. Also, the distortion of the anion geometries with respect to the geometries of the neutral parents are reduced with the methylation.

No abstract