ESR of the BC2 Molecule in Inert Matrices at 4°K

Abstract

The vapor in equilibrium with solid boron carbide at 2600°K, known to contain BC₂, B₂C, and BC molecules, has been trapped in argon and neon matrices and investigated by X‐band ESR spectroscopy. A strong spectrum characteristic of an axially symmetric ²Σ molecule was observed. Isotopic ¹⁰B, ¹¹B, and ¹³C substitution indicated that the molecule was either BC₂ or BC, and the latter could be eliminated because its ground state is probably ⁴Σ. The molecules were found to occupy several distinct sites in the matrices with preferential orientation of the internuclear axis perpendicular and parallel to the condensing surface. A representative set of magnetic parameters for BC₂ in neon is: $g_{\Vert }{\text{\hspace{0.17em}=\hspace{0.17em}2.0015, g⊥\hspace{0.17em}=\hspace{0.17em}1.9994, A}}_{\Vert }{(}^{11}\mathrm{B}\text{)\hspace{0.17em}=\hspace{0.17em}826.8}\mathrm{MHz}{\mathrm{,\; A\perp (}}^{11}\mathrm{B}\text{)\hspace{0.17em}=\hspace{0.17em}750.3}\mathrm{MHz}{\mathrm{,\; A}}_{\Vert }{(}^{13}\mathrm{C}\text{)\hspace{0.17em}=\hspace{0.17em}42.0}\mathrm{MHz}{\mathrm{,\; A\perp (}}^{13}\mathrm{C}\text{)=24.1}\mathrm{MHz}$ . Approximately 80% of the spin is on the boron atom, and the electronic structure can be appropriately depicted as ·B=C=C:.