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

• Published in: The Journal of chemical physics 1963-11, Vol.39 (10), p.2463-2473
• Main Authors: White, David, Seshadri, K. S., Dever, D. F., Mann, D. E., Linevsky, M. J.
• Format: Article
• Language: English
• ISSN: 0021-9606; 1089-7690
• DOI: 10.1063/1.1734049

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 (Vh) structure for which the O–Li–O angle and Li–O bond length are estimated to be 116° and 1.90 Å, respectively. Its B2u and B3u 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(Ag) = 400, ν2(Agt) = 250, ν3(B1g) = 300, ν4(B1u) = 270. Its ΔH0°(f) = +27.5+6 kcal/mole.