The electronic structure of the lithium trimer anion and cation

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Abstract
SCF and SCF–CI calculations have been performed on Li3, its anion and cation. We predict a value of 1.1 eV for the adiabatic electron affinity. The Li−3 bond energy is found to be 0.9 eV versus the 0.4 eV energy required to dissociate Li3 to dimer and atom. Thus, the bond strength of the anion considerably exceeds that of the neutral parent. The difference in the nature of electron binding to Li2 and Li3 can be understood through modification of simple MO concepts. The energy required to dissociate Li3+ to Li2++Li is found to be 1.28 eV. Hence, the bond strength of the cation also greatly exceeds that of the neutral. The Li3+ bond energy is comparable to the Li2+ dissociation energy (1.24 eV). The adiabatic ionization potential is found to be 3.95 eV. The combination of the present study and those of previous researchers indicates that the Li3 surface is weakly varying with bond angle and may be characterized by multiple minima. The current results for Li3 and Li3+ are discussed in the light of recent mass spectrometric studies of the trimer.