GAS PHASE, LASER PHOTOLUMINESCENCE OF $Ca_{2} B^{1} \Sigma_{u}^{+} - X {^{1}}\Sigma_{g}^{+}$; A NEW GROUND $STATE^{*}$
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Date
1979
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Ohio State University
Abstract
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 $Ca_{2} B ^{1} \Sigma^{+}_{u} - X^{1}\Sigma^{+}_{g}$. 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 $\omega_{e} y^{\prime\prime}_{e} \geq 73.18 (\pm 0.16), \omega_{e} x^{\prime\prime}_{e} = 0.560 (\pm 0.010)$ and $\omega_{e} y^{\prime\prime}_{e} = -1.59 \times 10^{-3} (\pm 0.17 \times 10^{-3}) cm^{-1}$. The dissociation energy is found to be $D_{o} \geq 2075 (\pm 150) cm^{-1}$. 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, $C^{1}\Sigma^{+}_{g}$, which correlates with $^{1}S = ^{1}D$ atoms. The equilibrium vapor pressure at 1400 K of ground state calcium molecules is estimated to be $\sim 5$ torr.
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$^{*}$This research was performed while at the Quantum Institute and Department of Physics, University of California, Santa Barbara, California 93106. Work supported by Air Force Office of Scientific Research, grant number 77-3138.
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