49 research outputs found
New Journal of Physics Measuring positron-atom binding energies through laser-assisted photorecombination
Abstract. Described here is a proposed experiment to use laser-assisted photorecombination of positrons from a trap-based beam and metal atoms in the gas phase to measure positron-atom binding energies. Signal rates are estimated, based in part upon experience studying resonant annihilation spectra using a trapbased positron beam. While positrons are important in many areas of science and technology including materials science, medicine and astrophysics, there are a number of open, fundamental questions regarding positron interactions with ordinary matter. One such topic is positron binding to atoms and molecules. There are accurate theoretical calculations of positron binding to atoms The goal of this paper is the development of a method to study positron-atom bound states using laser-assisted photorecombination, which should lead to enhanced annihilation
Stabilities of nanohydrated thymine radical cations: insights from multiphoton ionization experiments and ab initio calculations
Multi-photon ionization experiments have been carried out on thymine-water clusters in the gas phase. Metastable H2O loss from T+(H2O)n was observed at n ≥ 3 only. Ab initio quantum-chemical calculations of a large range of optimized T+(H2O)n conformers have been performed up to n = 4, enabling binding energies of water to be derived. These decrease smoothly with n, consistent with the general trend of increasing metastable H2O loss in the experimental data. The lowest-energy conformers of T+(H2O)3 and T+(H2O)4 feature intermolecular bonding via charge-dipole interactions, in contrast with the purely hydrogen-bonded neutrals. We found no evidence for a closed hydration shell at n = 4, also contrasting with studies of neutral clusters