Effect of dipole polarizability on positron binding by strongly polar molecules

Abstract

Abstract.A model for positron binding to polar molecules is considered by combining the dipole potential outside the molecule with a strongly repulsive core of a given radius. Using existing experimental data on binding energies leads to unphysically small core radii for all of the molecules studied. This suggests that electron-positron correlations neglected in the simple model play a large role in determining the binding energy. We account for these by including the polarization potential via perturbation theory and non-perturbatively. The perturbative model makes reliable predictions of binding energies for a range of polar organic molecules and hydrogen cyanide. The model also agrees with the linear dependence of the binding energies on the polarizability inferred from the experimental data [Danielson et al 2009 J. Phys. B: At. Mol. Opt. Phys. 42 235203]. The effective core radii, however, remain unphysically small for most molecules. Treating molecular polarization nonperturbatively leads to physically meaningful core radii for all of the molecules studied and enables even more accurate predictions of binding energies to be made for nearly all of the molecules considered.

Calculations of positron binding and annihilation in polyatomic molecules

“…The differences are due to using different values of the H-C and C≡N bond lengths (1.066 and 1.167 Å, respectively), and different electron and positron basis sets. 88 The value of ψ(r) on each contour is as follows (in a.u. ): black, 0.0002; red, 0.0003; dark blue, 0.0004; yellow, 0.0006; orange, 0.0008; light blue, 0.0012; green, 0.0016.…”

Reduction of OH vibrational frequencies in amino acids by positron attachment

“…A similar functional form was previously employed by Abdoul‐Carime and Desfrançois . Other functional forms have also been proposed to avoid unphysical divergency by Gribakin and Swann . Instead of applying other functional forms, we have examined the effect of the repulsive term on the calculated positron affinity values by changing the constant parameter C in the range of 0.9−1.3.…”

Mode coupling and multiquantum vibrational excitations in Feshbach-resonant positron annihilation in molecules

“…The resonant annihilation mechanism is operational only for the molecules that support positron bound states. The key parameters that determine the existence and strength of positron binding to neutral atoms and molecules, are the ionization energy I, dipole moment µ and dipole polarizability α d [6,7,[39][40][41][42]. Their values for three of the molecules studied here are listed in Table I.…”