Ab initio molecular orbital studies of the potential energy curves for the low lying triplet states of Be₂ and Be₃

Abstract

Ab initio calculations with uniform quality gaussian basis set were carried out at the RHF-SCF and CI level on the potential energy curves of the low lying triplet states of Be2 and Be3. The lowest excited state, the [Formula: see text] state of Be2 is 26.0 kcal/mol higher in energy than the ground [Formula: see text] state, and 39.4 kcal/mol lower than the separated Be(1S0) + Be(3P) atoms, with the s, p, d basis set. The next higher triplet state, the 3Πg, is only 8.7 kcal/mol above the lowest [Formula: see text] state. The [Formula: see text] and 3Πu states lie comparatively much higher than the [Formula: see text] state. All the triplet state potential curves have a bonding nature. The lowest triplet state [Formula: see text] in Be3 with D∞h symmetry lies ~15 kcal/mol above the ground [Formula: see text] state, and 48.2 kcal/mol lower than the separated atoms, 2Be(1S0) + Be(3P). The [Formula: see text] state has 1,3-diradical character and in all the higher triplet states α spin electrons are delocalized among the three Be atoms. The next higher triplet state 3Πu is 7.7 kcal/mol above the lowest [Formula: see text] state. The [Formula: see text] and 3Πg states lie much higher than the [Formula: see text] and 3Πu states. Like the triplet states of Be2, all Be3 triplet states have a bonding nature. Reaction path studies on the Be(3P) energy transfer reactions, [Formula: see text] and [Formula: see text] show that these reactions do not feature any activation energy barrier.

Long-range coefficients for the low-lying electronic states of BeLi and Be2

“…In this case, the difficulty comes from the accurate evaluation of the C 6 coefficient ͑and then of the imaginary frequency-dependent polarizabilities͒. However, it can be noted that the behavior at large distance for the two 2 1 Sϩ2 3 P and 2 1 Sϩ2 1 P interactions seems similar to the ones observed at short distance and given by Bruna et al 15 and Gosavi et al 16 The only apparent discrepancies concern the B 1 ⌺ u ϩ potential but we cannot definitely conclude to the repulsive or attractive behavior at distances shorter than the R LR criteria 16.7 and 18.5 a.u. for the singlet-triplet and the singlet-singlet interactions, respectively, if we do not take into account the totality of the exchange contribution.…”

“…Concerning this kind of molecule for which several theoretical studies have been reported, with results and predictions often quite contradictory, experimen-talists and theoreticians have recently focused specific attention on the study of their low-lying electronic states. 11,[14][15][16] With regard to the dissociative channels, these studies demonstrate that there is a need for high level ab initio investigations on the asymptotic long-range properties.…”

“…Very little is known about the potential curves of Be 2 . To our knowledge, only Bruna et al 15 and Gosavi et al 16 have recently studied the lower singlet and triplet molecular states using a MRDCI method and an ab initio ͓restricted Hartree-Fock-self-consistent-field plus configuration interaction (RHF-SCFϩCI)͔ technique, respectively. These states are relative to the first four dissociations: 2 1 Sϩ2 1 S, 2 1 Sϩ2 3 P, 2 1 Sϩ2 1 P, and 2 3 Pϩ2 3 P. The lowest ground-excited dissociation 2 1 S ϩ2 3 P gives rise to the bound 1 3 ⌺ u ϩ (2 g 2 2 u 3 g ) and 1 3 ⌸ g (2 g 2 2 u 1 u ) states and to the repulsive state at large distances 1 3 ⌸ u (2 g 2 2 u 1 g /2 g 2 u 2 1 g ).…”

“…If reliable values are available for atom-atom systems in which the atoms are in their ground state, very little is precisely known for excited atoms. There is a great current interest in the structure and chemical properties of small metal clusters, [6][7][8][9][10][11][12][13][14][15][16][17][18][19][20] notably those containing Group II elements characterized by weakly bound states and excited states. Experimental techniques combining YAG laser vaporization with collisional cooling are well suited to study weakly bound molecules of this kind.…”