Ground State of Gaseous CaO; a Study of the Matrix Spectra of Ca and CaO

The ¹P←¹S transition of Ca was studied in Kr and Xe at 20°K. The transition was shifted to the blue relative to the gas. The short‐wavelength component of the triplet shifted to the blue while the other two shifted to the red upon warming from 18 to 40°K. Codeposited Ca and Mg showed the same triplet structures with no shifts as when deposited individually in Xe thus confirming that the triplet structure is not due to long‐range interactions between metal atoms. CaO was synthesized in Kr and Xe by the reaction $\mathrm{Ca}{\text{+2O}}_2=\mathrm{CaO}+{\mathrm{O}}_3$ using ¹⁶O₂ and ¹⁸O₂. CaO showed a band system with the $\text{0–0}$ band in Xe at 20 130 cm⁻¹ and ${\omega }_e\text{′=890\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}{\mathrm{.\hspace{0.17em}\omega }}_e\text{″=794\hspace{0.17em}}{\mathrm{cm}}^{\text{−1}}$ from the infrared spectrum. The matrix spectra do not correspond to any of the analyzed singlet systems of CaO. It is concluded that the X ¹Σ state is not the ground state of CaO, which is probably a triplet.