Knowledge Bank

The $A2\Pi -X2\Sigma +(0,0)$ band of ZrN between 5620 and 5890 \AA has been studied using laser induced fluorescence, wavelength resolved fluorescence, and laser polarisation spectroscopy. All the 12 branches expected from a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi -2\Sigma$ transition have been observed and assigned. Severe perturbations in the $A2\Pi 3/2$ substate have been found. These perturbations were found at different J values for different isotopes. For $\mathrm{<mrow\; data-mjx-texclass="ORD">90</mrow>}ZrN$, the perturbations at $J=4.5$ and 8.5 of the e level and at $J=8.5$ and 18.5 of the f level of the $\Lambda$-doubling components of the $A2\Pi 3/2$ substate. The most probable perturbing state responsible for giving rise to those perturbations is a non-degenerate $\mathrm{<mrow\; data-mjx-texclass="ORD">4</mrow>}\Sigma -$ state. In addition, other degenerate perturbations found at $J=39.5,4.5$ and 56.5 are consistent with a $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Delta$ state being the perturbing state. The vibrational dependence and the negative sign of the spin-rotation parameter $\gamma$ observed in the ground state could arise from the interaction between the $X2\Sigma +$ with unobserved $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}\Pi$ states of open-shell electronic configuration. Least squares fittings have been performed to obtain accurate molecular constants of the $X2\Sigma +$ state.