Knowledge Bank

On excitation with energetic particles or VUV radiation. alkali halide crystals doped with $CN-$ display an ultraviolet spectrum which has been attributed1 to emission from an excited triplct state of $CM-$ to $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma +$ the ground state. This is despite the fact that there are expected to be no bound excited electronic states of $CM-$ hi vocuo. Although this metattable $(\tau -100ms.)$ species has previously been labeled $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ in anology with CO, there is some evidence it may be $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma +$ at in $N2$. We have computed the energies and spectroscopic properties of excited electronic states of $CN-$ stabilized by counterion lattices, employing an ab initio MCSCF approach. Results will be presented both for the ground $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma +$ state and for the low-lying $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ and $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Sigma +$ states. These may be directly compared with experiment. We will also discuss the accuracies of differing countercharge modle for simulating the effets of the lattice.