Is 9-acridinamine anion a dispersion-bound anion?

Abstract

The possibility of electron binding to 9-acridinamine ͑9-AA͒ was studied at the second order Møller-Plesset perturbation theory level with the aug-cc-pVDZ basis set augmented with a diffuse 6s6p4d set that has proven appropriate in earlier studies of weakly bound anions. It was found that both the amino and imino tautomers of 9-AA bind an excess electron to form stable anions. The vertical electron attachment energies corresponding to the amino and imino form were calculated to be 20 and 41 cm Ϫ1 , respectively. It was found that while the imino 9-AA tautomer forms a typical dipole-bound anion, the electron binding energy for the amino tautomer calculated at the electrostatic Koopmans' theorem level appears to be cancelled when the correlation correction to the dipole moment of the neutral is taken into account at the MP2 level. Therefore, the stability of the latter anion may be caused only by additional electron correlation effects, which are dominated by dispersion interactions. For this reason, we suggest that this anion may be termed a dispersion-bound anion.

Electron Binding Motifs of (H2O)n- Clusters

“…In contrast, the electron binding energy of the network permeating state of 16a is essentially independent of the strength of the electrostatic interactions, underscoring that the binding of the excess electron to this cluster is almost entirely due to correlation effects. For other correlation-bound excess electron species, see refs and . The cavity state of 24c displays intermediate behavior in that its binding energy decreases as the electrostatic interactions are decreased; however, it does not drop to zero, but rather, remains at about 30% of its original value as α → 0.…”

Molecular Anions

“…Of course, there has also been work done on binding electrons via charge-induced-dipole (i.e., polarization) interactions that has not used the kind of model potential discussed above. For example, Professor Piotr Skurski et al 203 examined electron binding to 9-acridinamine (Figure 4.18), which has a dipole moment of 3.1 D, so it should be able to bind an electron via charge-dipole interactions. However, they found that the binding energy of 6 cm -1 computed at the Koopmans' theorem (plus orbital relaxation) level, which includes the charge-dipole interaction, was canceled by the second-order correlation contribution to the EA excluding the dispersion interaction between the attached electron and the other electrons.…”

“…The second-order dispersion interaction was found to be 20 cm −1 and thus ultimately responsible for the final positive EA of this molecule. For this reason, ref calls this a dispersion-bound anion (i.e., an anion resulting from the r −6 dispersion coupling of the excess electron and the remaining electrons of 9-acridinamine).…”

“…The 9-acridinamine molecule whose anion is claimed to be dispersion-bound (Reprinted with permission from ref . Copyright 2001 American Institute of Physics).…”

Nonvalence Correlation-Bound Anion States of Polycyclic Aromatic Hydrocarbons

“…By definition, such anions are unbound in the Hartree–Fock approximation, and inclusion of long-range correlation effects is essential for the binding of the excess electron. It should be noted that there are also nonvalence anions where the electron is weakly bound in the absence of correlation effects but for which the stability is greatly enhanced by inclusion of correlation effects. − However, we consider here only anions that are unbound in the Hartree–Fock approximation. For these, when employing basis sets sufficiently flexible to describe the charge distribution of the anion, the wave function from the Hartree–Fock calculation collapses onto the neutral plus a discretized continuum orbital.…”