ESR and Optical Spectroscopy of the AlO Molecule at 4°K; Observation of an Al Complex and Its Interaction with Krypton

Abstract

The AlO molecule in its ²Σ ground state has been trapped in neon, argon, and krypton matrices at 4°K, and its ESR and optical spectra (infrared, visible, and uv) measured. In neon its magnetic parameters are $g_{\Vert }{\text{= 2.0015(3),\hspace{0.17em}g}}_{\perp }{\text{= 2.0004(3),\hspace{0.17em}A}}_{\Vert }{(}^{27}\mathrm{Al}\text{) = 872(1)}\mathrm{MHz}$ , and $A_{\perp }{(}^{27}\mathrm{Al}\text{) = 713(1)}\mathrm{MHz}$ . Δ_g⊥ is in accord with the magnitude and sign of the spin‐doubling constant, γ₀, determined in the gas phase. An infrared band at 924 cm⁻¹ in neon (917 cm⁻¹ in argon) is assigned to AlO: the large shift from the gas value of 965 cm⁻¹ indicates a highly ionic molecule. Besides the strong B ²Σ←X ²Σ absorption bands near 4500 Å, a progression of weak bands have been observed between 5500 and 11 000 cm⁻¹ and assigned to the A ²π_i←X ²Σ transition of AlO. ESR spectra of a weakly bonded $\mathrm{Al}–\mathrm{X}$ molecule (where X may be Al₂O) are observed in concentrated matrices; its magnetic properties are found to be very dependent upon the matrix gas used. In krypton matrices, ⁸³Kr hfs is also observed but disappears (reversibly) above about 35°K, suggesting the formation of a metastable $\mathrm{Kr}–\mathrm{AlX}$ complex.