An Analysis of the Infrared Absorption Spectrum of Am+3(5f6) in LaCl3

Abstract

The polarized infrared absorption spectrum of single crystals of Am⁺³(5f⁶) in LaCl₃ has been studied from 0.79 to 16.0 μ. In almost every instance the spectrum is sharp and completely polarized, and appears in definite groupings. Transitions from the ground level, ⁷F₀, to excited levels of the ground term, ⁷F₁, ⁷F₂, ⁷F₃, ⁷F₄, ⁷F₅, and ⁷F₆ have been observed. For the particular point symmetry C_3h that is consistent with experiment, magnetic‐dipole transitions are observed from the ⁷F₀ level to the ⁷F₁ level, and forced electric‐dipole transitions are observed to levels J = 2, 3, 4, 5, and 6. A theoretical analysis is presented for the crystal‐field split ⁷F_J levels. Using four parameters—A₂⁰〈r²〉=206 cm^—1, A₄⁰〈r⁴〉=—94.1 cm^—1, A₆⁰〈r⁶〉=—93.8 cm^—1, and A₆⁶〈r⁶〉=1100 cm^—1—excellent agreement is obtained between theory and experiment.