Knowledge Bank

Photoluminescence is observed when calcium metal vapor is illuminated with laser light in the 620-660 nm region. The resultant molecular bands are assigned to $Ca2B1\Sigma u+-X1\Sigma g+$. As observed in absorption by others using matrix isolation techniques at 4-10 K, the X state must be the ground electronic state. The gas phase vibrational constants for X are found to be $\omega eye\prime \prime \ge 73.18(\pm 0.16),\omega exe\prime \prime =0.560(\pm 0.010)$ and $\omega eye\prime \prime =-1.59\times 10-3(\pm 0.17\times 10-3)cm-1$. The dissociation energy is found to be $Do\ge 2075(\pm 150)cm-1$. The state previously assigned as the ground state has vibrational constants which significantly disagree with those found for X and is therefore reassigned to an excited electronic level, $C1\Sigma g+$, which correlates with $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}S=1D$ atoms. The equilibrium vapor pressure at 1400 K of ground state calcium molecules is estimated to be $\sim 5$ torr.