Infrared Emission Spectrum of Gaseous HBO2

The infrared emission spectrum of the vapor phase of the B₂O₃(l)–H₂O(g) system has been studied at elevated temperatures over the region 700–4000 cm^—1. Characteristic bands were found near 3680, 2030, and 1420 cm^—1, and approximate B¹⁰–B¹¹ and H–D isotope shifts measured. It is shown that these bands arise from the molecule HBO₂. The intensity of the 2030 cm^—1 band was studied as a function of both temperature and water pressure. The intensity vs temperature measurements lead to a heat of formation, ΔH₀^o, of —135.0±3 kcal/mole for HBO₂(g). The spectroscopic data, considered in the light of our analysis of the B₂O₃(g) infrared spectrum, are compatible with the structure $$\mathrm{O}=\mathrm{B}–{\mathrm{O}}_{–\mathrm{H}}$$ in which the OBO group is linear and the H is off‐axis. The force constants are found to resemble those determined for B₂O₃(g). Complete vibrational assignments are given for HBO₂(g) and its trimer (HBO₂)₃(g), a species which has recently been shown to exist in this system. Thermal functions have been computed for both molecules over a wide temperature range.