LASER INDUCED FLUORESCENCE IN CaO: A POPULATION PROBE FOR THE METASTABLE $a^{3}\Pi$ AND ${A'}^{1}\Pi$ STATES CaO

Abstract

$a^{3}\Pi$ and ${A^{\prime}}^{1}\Pi$ produced in the reaction of CaO with $N_{2}O$ or $O_{2}$ is excited with a tunable dye laser. The resultant laser induced fluorescence allows the populations of these states to be monitored. A dense and complex excitation spectrum is observed from 540 to 630 nm: fluorescence from a single mode laser (FWHM -- 20 MHz) is rarely extinguished as the laser is tuned. Excitation from $a^{3}\Pi$ results in population of an excited triplet which then emits back down to $a^{3}\Pi$ exhibiting P, Q, and R branches. All three $^{3}\Pi$ spin components are observed in excitation and at least two spin components are always observed in emission. Emission into ${A^{\prime}}^{1}\Pi$ is observed when excitation is from $a^{3}\Pi_{1}$. In addition, two sequences in the excitation spectrum with bands separated by less than 10 $cm^{-1}$ are attributed to ${A^{\prime}}^{1}\Pi$.