Photodissociation of CO2 to Produce CO(a 3Π)

Carbon dioxide in a helium buffer at room temperature was irradiated with a photon beam of wavelengths 1090 to 850 Å. ``Phosphorescence'' from the $\mathrm{CO}{\mathrm{(a\hspace{0.17em}}}^3{\mathrm{\Pi \; ‐\; X\hspace{0.17em}}}^1\mathrm{\Sigma )}$ Cameron bands was observed. The phosphorescent yield is zero at threshold and increases smoothly to a maximum of $\text{∼ 60\%}$ near 900 Å. The smoothness of the percentage yield was an unexpected observation and is explained by postulating that the relevant potential surface crossings are outside the Franck‐Condon region of CO₂ absorption. Approximate vibrational distributions have been determined and are also smooth functions of photon energy.