Competition between autoionization and radiative emission in the decay of excited states of the oxygen atom

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Abstract
High resolution relative photoionization cross sections are reported for a number of autoionizing states of atomic oxygen, including the metastable 3s″ 3P0, and 2s2p5 3P0 states. The wavelength resolution of the present data (0.04 Å, FWHM) is a factor of 4 better than that of the previously reported data, and is sufficient to allow observation of lifetime broadening for rapidly (LS‐allowed) autoionizing states. In addition, the present resolution separates nearly all of the fine structure components of the above‐mentioned 3P0 states. Autoionization, which is forbidden in an LS coupling scheme for these two 3P0 states, proceeds at a substantially reduced rate, and, consequently, radiative emission is a significantly competitive decay process. Since the autoionization rates of these states depend on the total angular momentum J of the decaying level, the lifetimes of the states and the branching ratios for autoionization versus radiative emission are different for each 3PJ0 fine structure level. The present high resolution autoionization data, which represent a significant improvement over the previous data, were combined with previously reported relative emission intensity data for these states to determine accurate branching ratios for autoionization versus emission. The lifetimes of these states were determined using the experimental branching ratios and the theoretical radiative emission rates calculated using the non‐closed‐shell many electron theory (NCMET) of Sinanoglu. The present work also reports lifetimes of ∼1×10−12 sec for the (LS‐allowed) autoionizing 3d′, 3S0, 3D0 and 4s′ 3D0 states, determined from observations of lifetime broadening of these spectral lines.

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