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

摘要

High resolution relative photoionization cross sections are reported for a number of autoionizing states of atomic oxygen, including the metastable 3sPrime;thinsp;3P0, and 2s2p5thinsp;3P0states. The wavelength resolution of the present data (0.04 Aring;, 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 (LShyphen;allowed) autoionizing states. In addition, the present resolution separates nearly all of the fine structure components of the abovehyphen;mentioned3P0states. Autoionization, which is forbidden in an LS coupling scheme for these two3P0states, 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 momentumJof the decaying level, the lifetimes of the states and the branching ratios for autoionization versus radiative emission are different for each3PJ0fine 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 nonhyphen;closedhyphen;shell many electron theory (NCMET) of Sinanoglu. The present work also reports lifetimes of sim;1times;10minus;12sec for the (LShyphen;allowed) autoionizing 3dprime;,3S0,3D0and 4sprime;thinsp;3D0states, determined from observations of lifetime broadening of these spectral lines.