Structure, vibrational frequencies, ionization energies, and photoelectron spectrum
of para-benzyne radical anion
V. Vanovschi, A.I. Krylov, and P.G. Wenthold
Theor. Chem. Acc., in press (2007)
Equilibrium structure, vibrational frequencies, and ionization energies of the
para-benzyne radical anion are characterized by coupled-cluster and
equation-of-motion methods. Vibronic interactions with the low-lying excited state result
in a flat potential energy surface along the coupling mode and even in lower-symmetry
C2v structures. Additional complications arise due to Hartree-Fock
instabilities and near-instabilities. The magnitude of vibronic interactions was
characterized by geometrical parameters, charge localization patterns and energy differences
between the D2h and C2v structures. The observed trends
suggest that the C2v minimum predicted by several theoretical methods is
an artifact of incomplete correlation treatment. The comparison between the calculated and
experimental spectrum confirmed D2h structure of the anion, as well as
accuracy of the coupled-cluster and spin-flip structures, frequencies and normal modes of
the anion and the diradical. Density functional calculations (B3LYP) yielded only a
D2h minimum, however, the quality of the structure and vibrational
frequencies is poor, as follows from the comparison to high-level wave function calculations
and the calculated spectrum. The analysis of charge localization patterns and the performance
of different functionals revealed that B3LYP underestimates the magnitude of vibronic
interactions due to self-interaction error.
Calculated and experimental photodetachment spectra of p-benzyne anion. The spectrum is
computed within double-harmonic Condon approximation using structures and frequencies computed by equation-of-motion
coupled-cluster methods.
