THE GREEN BANDS OF CaO: OODR SPECTROSCOPY AND ELECTRONIC STRUCTURE MODEL
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Date
1987
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Publisher
Ohio State University
Abstract
The CaO Green and Orange Systems are so complex that their attribution to CaO rather than a polyatomic species was in doubt until recently. Excluding all $^{1}\Sigma^{+}$ states, the electronic structure of CaO may be understood as $Ca^{+}O^{-}$ where the $Ca^{+}$ structure $(X_{0},A_{\pi},B_{\sigma} Ca^{+}$ centered orbitals) is well represented by a ligand field model for the $Ca-monohalides^{1}$ and an O- p-hole ($\sigma-1$ or $\pi^{-1}$). All prominent features of the CaO Orange system have been assigned as transitions between five $A^{-1}$ upper states and two $X_{\sigma}{^{-1}}$ lower states $(a^{3}\pi, A^{\prime}1\pi)$. The model predicts that the Green System will consist of $B_{0\pi}{^{-1}} {^{1,3}}\pi_{i}-x_{\sigma \pi}{^{-1}}{^{1,3}}\pi_{i}$ transitions analogous to the Green CaF $B^{2}\Sigma^{+}-X^{2}\Sigma^{+}$ system. Laser excitation-resolved fluorescence spectroscopy has confirmed the predicted assignments of the upper and lower states of the CaO Green System. Rotation-vibration analysis of this exceedingly congested system requires a sub-Doppler Optical Optical Double Resonance (OODR) scheme linked via a common lower level in order to select a single J, e/f, component. Preliminary measurements show $T_{O}$ and $B_{O}$ values for the $B_{\sigma \pi}^{-1}$ state of 26 $348 cm^{-1}$ and $0.353(4) cm^{-1}$. This newly discovered 1* state lies only $435 cm^{-1}$ above and has a $B_{O}$-value $0.033 cm^{-1}$ (i.e. 9\%) smaller than the known $B_{1}\pi$ state. This is in accord with the $A_{\pi \sigma}{^{-1}}$ configuration of $B^{1}\pi$ and provides further evidence for the almost perfect separation of the CaO electronic spectrum into $\pi^{-1}$ and $\sigma^{-1}$ sub-manifolds.
Description
$^{1}$ S.F. Rice, H. Martin, and R.W. Field, J. Chem. Phys. 82, 5023 (1985).
Author Institution: Department of Chemistry, Massachusetts Institute of Technology
Author Institution: Department of Chemistry, Massachusetts Institute of Technology