The radiative lifetime of metastable CO (aΠ, v = 0)

We present a combined experimental and theoretical study on the radiative lifetime of CO in the aΠ1,2, v = 0 state. CO molecules in a beam are prepared in selected rotational levels of this metastable state, Stark-decelerated and electrostatically trapped. From the phosphorescence decay in the trap, the radiative lifetime is measured to be 2.63 ± 0.03 ms for the aΠ1, v = 0, J = 1 level. From spin-orbit coupling between the aΠ and the AΠ state a 20% longer radiative lifetime of 3.16 ms is calculated for this level. It is concluded that coupling to other Π states contributes to the observed phosphorescence rate of metastable CO.