Knowledge Bank

Theoretical expressions for the vibrational energy levels of a linear triatomic molecule in a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta$ electronic state have been derived. It is found that the coupling of the electronic and vibrational angular momenta in a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta$ electronic state (Renner-Teller effect) causes splittings of the vibrational energy levels. These splittings are similar to those observed for $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ states (which have been treated theoretically by People), but with certain small differences. A comparison is made between theory and the experimental results for the CCN radical.