Stick diagram of the p-nitroaniline molecule showing the donor (NH2) and acceptor (NO2) moieties responsible for the large dipole moment of this molecule.
Schematic of the CID apparatus (QStar Elite TOFMS) showing the quadrupole Q1 for isolation of the electrospray ions and the collision region containing argon gas (CAD) followed by product ion identification by the TOF Mass Spectrometer. Differential pumping occurs at each chamber as shown along with approximate operating pressures in each region.
The photoelectron spectrum of the valence p-nitroaniline anion recorded at 2.54 eV photons. The EAa is estimated as the signal onset at 0.75 ± 0.1 eV and a VDE of 1.1 eV.
Appearance of fragments caused by collision of [pNA-H]− with argon at lab frame energies of 9 eV, 12 eV, and 17 eV. Relative abundances are normalized to the parent anion peak.
Nonlinear fits of the CID cross-section of [pNA-H]− into (a) [pNA-H-NO]− and (b) NO2 −.
Natural orbitals from EA-EOM-CCSD/Aug-cc-pVDZ+ calculations for the two lowest states of the pNA− anion. At the C2v symmetrical transition state the two lower states of the anion have different symmetries, 2A1 and 2B1. Therefore, they are completely decoupled, and can be characterized as dipole-bound and valence. (a) shows the 80% enclosing iso-surface of the dipole-bound state and (b) shows the 90% enclosing iso-surface of the valence state. Note the different length scale of the two figures; ⟨|r|⟩ is 8.5 Å for the natural orbital of the dipole-bound state and just 2.6 Ǻ for that of the valence state.
Natural orbitals from EA-EOM-CCSD/Aug-cc-pVDZ+ calculations for the two lowest states of the pNA− anion. At the Cs symmetrical minimal energy geometry, the two lower states of the anion both have 2A′ symmetry are strongly coupled, and can not consequently be characterized as either dipole-bound or valence. Eighty-percent enclosing iso-surfaces of the first and second states are shown in (a) and (b), respectively. Note the comparable length scale of the two figures; ⟨|r|⟩ of the respective natural orbital is 4.3 Å for the lower and 6.8 Å for the higher state.
Dissociation barrier energies of [pNA-H]−. Calculated energies are the difference between deprotonated pNA and the transition state.
Vertical electron affinities, in meV, computed with the EA-EOM-CCSD method. The standard augmented double-ζ and triple-ζ basis set were further augmented with a 6s6p6d set of extra diffuse functions at the center of mass of the molecule. At the C2v symmetric transition state dipole-bound states have A1 symmetry while the valence state has B1 symmetry. In Cs symmetry all bound states have A′ symmetry, and only the third state can be characterized as dipole-bound, whereas the lower two states show a mixed character.
Vertical detachment energy, in eV, computed with different methods and basis sets. Two geometries are considered, the Cs symmetrical minimal energy structure of the pNA anion, and the associated C2v symmetrical transition state of the NH2 inversion.
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