Ab initio study for the low-lying electronic states of Al3 and Al3−: The photoelectron spectroscopy of Al3−

Abstract

The low-lying electronic states of Al3 (2A1,2B1,4A2,4B1,2B2,2A1,4B2,6A2) and Al3− (1A1,3B2,3A1,3A2,3B1,5A2) are studied by coupled-cluster methods with a [6s5p2d1f] basis set. The geometries and harmonic frequencies are calculated by the coupled-cluster single double triple (CCSD(T)) correlation method with frozen core and virtual molecular orbitals. The energetic splittings at CCSD(T) geometries are calculated also by the CCSDT method. The calculated vibrational frequencies of the observed states of Al3 (A12, B12, and A24) and Al3− (A11 and B23) are in excellent agreement with experimental results. Other frequencies of this work are expected to be correct within ±20 cm−1. It is shown that A24–B14(E″4) and B22–A12(E′2) of Al3 as well as B23–A13(E′3) and A23–B13(E″3) of Al3− are pairs of minima and transition states on a potential energy surface of a pseudorotation of the corresponding degenerate states. The vertical excitation energies of additional states of Al3(2E′,4E′,2A1′) and Al3−(1E″,1E′) are calculated by the electron-excitation equation-of-motion CC method and the electron-attachment equation-of-motion CC method. The possible processes of ionizations and vibronic transitions are analyzed based on the calculated results. All features of the recent photoelectron spectroscopic study of Al3− are explained consistently. It is also shown that the photoelectron signals of electron binding energies of 2.65 and 4.4 eV in earlier experiments correspond to the ionization of the ground state of Al3− to higher-lying excited states of Al3. The two states of the resonant two-photon ionization experiment are assigned to the lowest quartet state and the third quartet state, E″4→E′4, without ambiguity. The anticipated features of five more electronic excitations with transition energies of 0.22, 0.69, 0.77, 0.98, and 1.06 eV are discussed.

A study of the ground and excited states of Al3 and Al3−. II. Computational analysis of the 488nm anion photoelectron spectrum and a reconsideration of the Al3 bond dissociation energy

“…Subsequent computational studies suggested that the 2.57 eV feature is due to a transition ͑X1͒ from the Al 3 − ground state to this 2 B 2 state. 5 According to the present calculations ͑Table I͒, the adiabatic electron detachment energy for this transition is 2.654 eV ͑CC͒, in agreement with the observed value. In addition, the two-electron nature of this transition would be consistent with the relatively weak observed intensity of the 2.57 eV band.…”

“…For the 4.3 eV band B, 36 reported as C at 4.4 eV in the earlier UV study, 37 an alternative assignment has been suggested based on equation-of-motion CC calculations at the Al 3 ground state geometry. 5 This transition ͑X2͒ is to a 2 A 1 Ј͑ 2 A 1 ͒ ͑͑1a 2 Љ͒ 0 ͑2a 1 Ј͒ 2 ͑3a 1 Ј͒ 1 ͒ state with a calculated energy of 2.45 eV above the Al 3 ground state, giving a predicted photodetachment energy of 4.39 eV. 5 This 2 A 1 Ј͑ 2 A 1 ͒ state, which would require a two-electron process to be accessed from the Al 3 − ground state, was not identified in the present PBE0 or time dependent PBE0 calculations.…”

“…Small aluminum clusters provide a topic accessible to a variety of spectroscopic and computational approaches, enabling the insights gained by each method to check and elucidate the others. While simple enough to be characterized by both wave function theory [1][2][3][4][5][6][7][8][9][10][11][12][13][14] and density functional theory ͑DFT͒, [15][16][17][18][19][20][21] small aluminum clusters also share some properties in common with the more electronically complex transition metal clusters. These include the ability to form bothand -type bonds and the presence of low-energy electronic states with different spin multiplicities.…”

Probing the structural and electronic properties of boron cluster anions doped with one or two aluminum atoms

“…1, all possible AlB À 2 geometries such as C 2v and C 1v isomers are optimized as the stable structures. The calculated results illustrate that the isosceles triangle 2a isomer with the symmetry of C 2v and electronic state of 1 A 1 is the lowest-energy structure, which can be regarded as two substitutions of Al atoms by B atoms in a triangle Al À 3 anion [17,20,21] and can also be viewed as a substitution of a B atom by an Al atom in the equilateral triangle B À 3 cluster [12]. The energetically closest isomer 2b is a triplet state with C 1v symmetry, which is consistent with that offered in Ref.…”

“…These studies have confirmed the planar or quasi-planar structures are more stable than any three-dimensional structures for an extended size range at least up to n = 23. While for the aluminum atom belonging to the same group with that of the boron atom in the periodic table, the structure transition of the Al n clusters from planar to three-dimensional (3D) occurs at n = 5 [16][17][18][19][20][21][22][23][24]. The substitution of boron clusters by aluminum atoms provides unique chemical environment, which may induce a significant change of the electronic properties and the possibility of new types of materials.…”