Knowledge Bank

Spectroscopic observations from 190 to 800 nm of a fast-flowing helium afterglow have shown CO (a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$) is a major product of the reaction of He (2 $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}$S) metastable atoms with carbon dioxide. Studies carried out in a helium bath at pressures near 1 torr have proved convenient for observing the long lived triplet of CO by means of the emission between 190 and 260 nm of the Cameron Bands, the a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ --- X $\mathrm{<mrow\; data-mjx-texclass="ORD">1</mrow>}\Sigma$ system. Measurements of the decay of the CO a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ emission as a function of distance in the flowing helium have been used to measure the radiative lifetime of the a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$ state and the quenching of this state by $CO2$ and by helium. Rates of removal of the CO (a $\mathrm{<mrow\; data-mjx-texclass="ORD">3</mrow>}\Pi$) by $CO2$ and He at room temperature over the pressure range from 0.1 to 3 torr have been measured as $(1.6\pm 0.3)\times 10-11$ $cm3$ $sec-1$ and $(6\pm 3)\times 10-14$ $cm3$ $sec-1$, respectively. The radiative lifetime was found to be between 2.5 and 20 msec.