Infrared Spectra and the Structures and Thermodynamics of Gaseous LiO, Li2O, and Li2O2

Abstract

The vapor above heated lithium oxide (Li₂O) has been investigated mass spectrometrically and by infrared matrix‐isolation spectroscopy. The vapor composition and Knudsen effusion rates were measured as functions of temperature, and the matrix spectra of the principal lithium oxide species—Li₂O, LiO, Li₂O₂—identified and analyzed for different isotopic abundances. The predominant vapor species Li⁷₂O is probably linear with r(Li–O) = 1.59 Å, and has fundamentals ν₁, ν₂, ν₃ at [760], [140], and 987 cm^—1, respectively. Its heat of formation ΔH₀°(f) = —43.7±2.5 kcal/mole. The diatomic molecule Li⁷O has ν = 745 cm^—1, an estimated bond length r = 1.62 Å, and ΔH₀°(f) = +16.0±5 kcal/mole. The previously undetected molecule Li⁷₂O₂ is shown to resemble the alkali halide dimers in having a planar rhombic (V_h) structure for which the O–Li–O angle and Li–O bond length are estimated to be 116° and 1.90 Å, respectively. Its B_2u and B_3u frequencies are found at 324 and 522 cm^—1, respectively, in a krypton matrix. The remaining unobserved modes are estimated in cm^—1 as follows: ν₁(A_g) = 400, ν₂(A_g^t) = 250, ν₃(B_1g) = 300, ν₄(B_1u) = 270. Its ΔH₀°(f) = +27.5+6 kcal/mole.