Infrared matrix isolation of hydrogen-bonded complexes between acetone and hydrogen iodide. Irradition and temperature effets

Abstract

Co-condensation of acetone h₆ or d₆ with HI and DI in an excess of argon or nitrogen allows identification of several kinds of hydrogen-bonded complexes. The 1:1 species which predominates at high dilution exists under two forms: a non-hydrogen-bonded one (U) and a hydrogen-bonded one (C) trapped in two sites. The C→ U conversion is mainly induced by i.r. radiation in the range 1500–2200 cm^–1 corresponding to the excitation of H(D)I stretching mode. The U → C conversion is governed by temperature with an activation energy of 2.5 kJ mol^–1. A 1:2 acetone-(HI)₂ complex with a chain arrangement of the acid ligands is also sensitive to the infrared beam of the spectrometers. In the presence of an excess HI another aggregate insensitive to infrared radiation has been identified with strong perturbations of the acetone submolecule, suggesting a double attack of the oxygen by bifurcated chain of several HI molecules. Finally, for an excess of acetone an ionic species of the type (acetone)₂ H⁺I^– is identified by a strong band at 600 cm^–1 typical of a centrosymmetric minimum potential well for the proton.