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Probing the Critical Dipole Moment To Support Excited Dipole-Bound States in Valence-Bound Anions
journal contribution
posted on 2019-10-10, 17:33 authored by Chen-Hui Qian, Guo-Zhu Zhu, Lai-Sheng WangWe
report photodetachment spectroscopy and high-resolution photoelectron
imaging of para-halogen substituted phenoxide anions, p-XC6H4O– (X = F,
Cl, Br, I). The dipole moments of the p-XC6H4O neutral radicals increase from 2.56 to 3.19 D for
X = F to I, providing a series of similar molecules to allow the examination
of charge-dipole interactions by minimizing molecule-dependent effects.
Excited DBSs ([XC6H4O]*–)
are observed for the four anions with binding energies of 8, 11, 24,
and 53 cm–1, respectively, for X = F to I, below
their respective detachment thresholds. The binding energies exhibit
a linear correlation with the dipole moments of the neutral radicals,
extrapolating to a critical dipole moment of 2.5 D for zero binding
energy. Because of the small binding energy of the excited DBS of
[FC6H4O]*–, rotational autodetachment
is observed to compete with vibrational autodetachment in the resonant
photoelectron spectra, resulting in electrons with near zero kinetic
energies.