Etude spectroscopique des dérivés du peroxyde d'hydrogène. IV. L'acide de Caro, H2SO5

Abstract

The i.r. and laser Raman spectra of pure, crystalline Caro's acid, H2SO5, were measured for the first time between 4000 and 30 cm−1. Most of the fundamental vibrations of the molecule could be identified by comparison with those of the H2SO4, H2O2 and HSO5− species. In addition, a dozen or so of lattice modes were recorded. The O—O stretching frequency is slightly higher (886 cm−1) than in solid H2O2, contrary to expectation. The two hydroxyl groups are quite different, both chemically (Caro's acid is essentially monobasic) and spectroscopically. The ionizable OH group forms strong intermolecular hydrogen bonds, as in H2SO4. However, the non-ionizable O2H group is engaged mainly in intramolecular hydrogen bonding. The unit cell of the crystalline acid must contain more than two molecules.