The photoionization cross section for the positronium (Ps) negative ion, Ps−, at the lowest n = 2 Feshbach resonance, estimated by neglecting the influences of the weakly bound outer electron, is σF = 1.4 × 10−12 cm2, about 3 × 103 times the existing lower limit calculated by Igarashi and co-workers (New J. Phys. 2, 17 (2000)). Although the estimated cross section is 200 times smaller than the analogous cross section for photoexcitation of the Ps Lyman-α transition, including the effect of the broad line width of the resonance shows it will be feasible to observe this resonance to obtain precision information about the three body Ps− system.The photoionization cross section for the positronium (Ps) negative ion, Ps−, at the lowest n = 2 Feshbach resonance, estimated by neglecting the influences of the weakly bound outer electron, is σF = 1.4 × 10−12 cm2, about 3 × 103 times the existing lower limit calculated by Igarashi and co-workers (New J. Phys. 2, 17 (2000)). Although the estimated cross section is 200 times smaller than the analogous cross section for photoexcitation of the Ps Lyman-α transition, including the effect of the broad line width of the resonance shows it will be feasible to observe this resonance to obtain precision information about the three body Ps− system.

Canadian Journal of PhysicsJul 29, 201312 citations

Photoionization of atomic ions

Hannelore E. Saraph

Jan 1, 19860 citations

Calculations of some weakly bound diatomic molecular negative ions

Yong Li, C. D. Lin

We examine the existence of stable bound states of some diatomic molecular ions where the neutral molecule itself is either unbound or barely bound. Two bound states have been found for the ${\mathrm{HeH}}^{\ensuremath{-}}$ ion even though HeH is known to be unbound. We have found no bound states for ${\mathrm{He}}_{2}^{\ensuremath{-}}$ even though ${}^{4}{\mathrm{He}}_{2}$ is known to have one bound state. The predicted binding energies for ${\mathrm{HeH}}^{\ensuremath{-}}$ are of the order of 1 K and depend sensitively on the isotope combinations. Other weakly bound negative ions such as ${\mathrm{NeH}}^{\ensuremath{-}}$ and ${\mathrm{ArH}}^{\ensuremath{-}}$ have also been investigated. These weakly bound molecular ions are good candidates for cold collision experiments.We examine the existence of stable bound states of some diatomic molecular ions where the neutral molecule itself is either unbound or barely bound. Two bound states have been found for the ${\mathrm{HeH}}^{\ensuremath{-}}$ ion even though HeH is known to be unbound. We have found no bound states for ${\mathrm{He}}_{2}^{\ensuremath{-}}$ even though ${}^{4}{\mathrm{He}}_{2}$ is known to have one bound state. The predicted binding energies for ${\mathrm{HeH}}^{\ensuremath{-}}$ are of the order of 1 K and depend sensitively on the isotope combinations. Other weakly bound negative ions such as ${\mathrm{NeH}}^{\ensuremath{-}}$ and ${\mathrm{ArH}}^{\ensuremath{-}}$ have also been investigated. These weakly bound molecular ions are good candidates for cold collision experiments.

Physical Review ASep 1, 199941 citations

Photoionization of atoms near threshold

Juha Javanainen

Optics CommunicationsJul 1, 198331 citations

Negative-ion photodetachment in an electric field

Hin-Yiu Wong, A. R. P. Rau, Chris H. Greene

A multichannel study of the photodetachment of a negative ion such as ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$ in the presence of a constant electric field is presented. The analysis is carried out as a series of frame transformations for the outgoing photoelectron. An earlier analysis in the absence of the external field is now augmented by the further transformations from spherical to cylindrical symmetry that are required. The interplay between the various thresholds due to fine structure in the negative ion and residual atom and the effects of the external field are analytically treated. The net effect is to eliminate the thresholds, to induce modulations in the detachment cross section, and to introduce field-assisted-tunneling contributions to the photodetachment. Numerical illustrations are provided. Our treatment closely parallels similar treatments of photoionization of neutral atoms in an electric field and of photodetachment in a magnetic field.A multichannel study of the photodetachment of a negative ion such as ${\mathrm{S}}^{\mathrm{\ensuremath{-}}}$ in the presence of a constant electric field is presented. The analysis is carried out as a series of frame transformations for the outgoing photoelectron. An earlier analysis in the absence of the external field is now augmented by the further transformations from spherical to cylindrical symmetry that are required. The interplay between the various thresholds due to fine structure in the negative ion and residual atom and the effects of the external field are analytically treated. The net effect is to eliminate the thresholds, to induce modulations in the detachment cross section, and to introduce field-assisted-tunneling contributions to the photodetachment. Numerical illustrations are provided. Our treatment closely parallels similar treatments of photoionization of neutral atoms in an electric field and of photodetachment in a magnetic field.

Physical Review AApr 1, 198859 citations

{}^{4}{\mathrm{He}}_{2}

is known to have one bound state. The predicted binding energies for ${\mathrm{HeH}}^{\ensuremath{-}}$ are of the order of 1 K and depend sensitively on the isotope combinations. Other weakly bound negative ions such as ${\mathrm{NeH}}^{\ensuremath{-}}$ and ${\mathrm{ArH}}^{\ensuremath{-}}$ have also been investigated. These weakly bound molecular ions are good candidates for cold collision experiments.