Infrared Absorption Spectra of B2O3, B2O2, and BO2 in Solid Argon Matrices

The infrared absorption spectra of B₂O₃, B₂O₂, and BO₂ isolated in solid argon matrices have been investigated in the region 350–4000 cm^—1. The visible absorption spectrum of matrix‐isolated BO₂ was observed in the region 4000–5500 Å. The gaseous species were generated in a high‐temperature effusion cell and trapped under conditions of moderate to high dilution in solid argon matrices at approximately 4°K. Bands were found at 1955, 1921, 1899, 1323, and 1276 cm^—1 in the infrared spectra of B₂¹⁰O₂, B¹⁰B¹¹O₂, B₂¹¹O₂, and B¹⁰O₂, and B¹¹O₂, respectively. For both B₂¹⁰O₃ and B₂¹¹O₃ infrared spectra of the most dilute matrices show seven distinct bands in the region 450–2100 cm^—1. Six of these can be readily assigned as fundamentals and their relative intensities explained if the known ``V'' structure of B₂O₃ is supposed to have a larger apex angle than that determined by electron diffraction, and the correlation of the normal vibrations and selection rules with those for the linear symmetric (D_∞h) model is considered. With additional help from the measured B¹⁰–B¹¹ isotope shifts and force constant calculations the following complete assignment was obtained (all frequencies in cm^—1): $$\begin{array}{c}{\mathrm{B}}_2^{10}{\mathrm{O}}_3{\text{:\hspace{0.17em}\hspace{0.17em}2128(A}}_1{\text{),733(A}}_1{\text{),536(A}}_1{\text{);[172](A}}_1\mathrm{),}\mathrm{or}{\text{\hspace{0.17em}[260](A}}_1{\text{);[476](A}}_2{\text{)\hspace{0.17em}2128(B}}_1{\text{),1242(B}}_1{\text{),471(B}}_1{\text{);493(B}}_2\mathrm{);}\\ {\mathrm{B}}_2^{11}{\mathrm{O}}_3{\text{:\hspace{0.17em}\hspace{0.17em}2060(A}}_1{\text{),729(A}}_1{\text{),518(A}}_1{\text{),[172](A}}_1\mathrm{),\hspace{0.17em}}\mathrm{or}{\text{\hspace{0.17em}[259](A}}_1{\text{);[456](A}}_2{\text{),2060(B}}_1{\text{),1239(B}}_1{\text{),454(B}}_1{\text{);477(B}}_2\mathrm{);}\end{array}$$ where the bracketed frequencies were not observed directly. Thermal functions have been computed for B₂O₃ and compared with the available calorimetric data. Structural parameters and a complete vibrational assignment have been estimated for B₂O₂. The infrared and green bands observed for BO₂ are in agreement with the high‐resolution results of Johns. Thermal functions for B₂O₂ and BO₂ have also been computed.