Boron trifluoride ($\mathrm{B}{\mathrm{F}}_3$)

An isolated boron trifluoride molecule has trigonal planar molecular geometry and the D3h molecular point group. Its three equal fluorine contributions give $I_{\parallel }=3m_{\mathrm{F}}{R}^2$ and $I_{\perp }=3m_{\mathrm{F}}{R}^2/2$ in the rigid rotor approximation.