147 research outputs found
Electron affinities of the first- and second- row atoms: benchmark ab initio and density functional calculations
A benchmark ab initio and density functional (DFT) study has been carried out
on the electron affinities of the first- and second-row atoms. The ab initio
study involves basis sets of and quality, extrapolations to
the 1-particle basis set limit, and a combination of the CCSD(T), CCSDT, and
full CI electron correlation methods. Scalar relativistic and spin-orbit
coupling effects were taken into account. On average, the best ab initio
results agree to better than 0.001 eV with the most recent experimental
results. Correcting for imperfections in the CCSD(T) method improves the mean
absolute error by an order of magnitude, while for accurate results on the
second-row atoms inclusion of relativistic corrections is essential. The latter
are significantly overestimated at the SCF level; for accurate spin-orbit
splitting constants of second-row atoms inclusion of (2s,2p) correlation is
essential. In the DFT calculations it is found that results for the 1st-row
atoms are very sensitive to the exchange functional, while those for second-row
atoms are rather more sensitive to the correlation functional. While the LYP
correlation functional works best for first-row atoms, its PW91 counterpart
appears to be preferable for second-row atoms. Among ``pure DFT'' (nonhybrid)
functionals, G96PW91 (Gill 1996 exchange combined with Perdew-Wang 1991
correlation) puts in the best overall performance. The best results overall are
obtained with the 1-parameter hybrid modified Perdew-Wang (mPW1) exchange
functionals of Adamo and Barone [J. Chem. Phys. {\bf 108}, 664 (1998)], with
mPW1LYP yielding the best results for first-row, and mPW1PW91 for second-row
atoms. Indications exist that a hybrid of the type mPW1LYP +
mPW1PW91 yields better results than either of the constituent functionals.Comment: Phys. Rev. A, in press (revised version, review of issues concerning
DFT and electron affinities added
Action spectroscopy of gas-phase carboxylate anions by multiple photon IR electron detachment/attachment
We report on a form of gas-phase anion action spectroscopy based on infrared
multiple photon electron detachment and subsequent capture of the free
electrons by a neutral electron scavenger in a Fourier Transform Ion Cyclotron
Resonance (FTICR) mass spectrometer. This method allows one to obtain
background-free spectra of strongly bound anions, for which no dissociation
channels are observed. The first gas-phase spectra of acetate and propionate
are presented using SF6 as electron scavenger and a free electron laser as
source of intense and tunable infrared radiation. To validate the method, we
compare infrared spectra obtained through multiple photon electron
detachment/attachment and multiple photon dissociation for the benzoate anion.
In addition, different electron acceptors are used, comparing both associative
and dissociative electron capture. The relative energies of dissociation (by
CO2 loss) and electron detachment are investigated for all three anions by DFT
and CCSD(T) methods. DFT calculations are also employed to predict vibrational
frequencies, which provide a good fit to the infrared spectra observed. The
frequencies of the symmetric and antisymmetric carboxylate stretching modes for
the aliphatic carboxylates are compared to those previously observed in
condensed-phase IR spectra and to those reported for gas-phase benzoate,
showing a strong influence of the solution environment and a slight substituent
effect on the antisymmetric stretch.Comment: Revised version, Submitted to J Phys Chem
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