The characterisation of molecular boric acid by mass spectrometry and matrix isolation infrared spectroscopy

When crystalline orthoboric acid is heated in vacuo to ca. 40 °C, it vaporises to yield molecular H3BO3. The i.r. spectrum of this species isolated in low-temperature nitrogen matrices shows characteristic absorptions at 3 668.5 (E′), 1 426.2 (E′), 1 009.9 (E′), 675.0 (A″), 513.8 (A″), and 448.9 (E′) cm–1 consistent with C3h symmetry. These spectral assignments are supported by extensive isotope labelling, and by a partial normal co-ordinate analysis.