A study of the ground and excited states of Al 3 and Al 3 -. II. Computational analysis of the 488 nm anion photoelectron spectrum and a reconsideration of the Al 3 bond dissociation energy

Stephen R. Miller, Nathan E. Schultz, Donald G. Truhlar, Doreen G. Leopold

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Computational results are reported for the ground and low-lying excited electronic states of Al3- and Al3 and compared with the available spectroscopic data. In agreement with previous assignments, the six photodetachment transitions observed in the vibrationally resolved 488 nm photoelectron spectrum of Al 3 - are assigned as arising from the ground X̃ 1A ′ 1 (1A 11) and excited 2B 3 states of Al3- and accessing the ground X̃ A1′2 (A12) and excited A 2″2 ( 2B 1), A24, and B22 states of Al 3 (with C 2v labels for D 3h states in parentheses). Geometries and vibrational frequencies obtained by PBE0 hybrid density functional calculations using the 6-311+G (3d2f) basis set and energies calculated using coupled cluster theory with single and double excitations and a quasiperturbative treatment of connected triple excitations (CCSD(T)) with the aug-cc- pVxZ { x=D, T, Q} basis sets with exponential extrapolation to the complete basis set limit are in good agreement with experiment. Franck-Condon spectra calculated in the harmonic approximation, using either the Sharp-Rosenstock-Chen method which includes Duschinsky rotation or the parallel-mode Hutchisson method, also agree well with the observed spectra. Possible assignments for the higher-energy bands observed in the previously reported UV photoelectron spectra are suggested. Descriptions of the photodetachment transition between the Al 3- and Al 3 ground states in terms of natural bond order (NBO) analyses and total electron density difference distributions are discussed. A reinterpretation of the vibrational structure in the resonant two-photon ionization spectrum of Al 3 is proposed, which supports its original assignment as arising from the X̃ 2A 1′ ground state, giving an Al 3 bond dissociation energy, D0 (Al 2 -Al), of 2.403±0.001 eV. With this reduction by 0.3 eV from the currently recommended value, the present calculated dissociation energies of Al 3, Al 3-, and Al 3+ are consistent with the experimental data.

Original languageEnglish (US)
Article number024304
JournalJournal of Chemical Physics
Issue number2
StatePublished - 2009

Bibliographical note

Funding Information:
We thank Dr. Michael Morse, Dr. Kent Ervin, and Dr. Susan Green for helpful discussions. This research was supported by the National Science Foundation under Grant No. CHE07-04974 (D.G.T), by the Research Corporation (D.G.L.), and by computer resources provided by the Minnesota Supercomputing Institute.


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