Knowledge Bank

The transitions $f―4\Pi g(\upsilon -2,3)leftarrowa―4\Pi u(\upsilon -5,6)$ are observed at high resolution in $\mathrm{<mrow\; data-mjx-texclass="ORD">16,16</mrow>}O2+,\mathrm{<mrow\; data-mjx-texclass="ORD">16,18</mrow>}O2+$, and $^\{\{18,\; 18\}O\_\{2\}\}^\{+\}$ using ion photofragment spectroscopy. These vibrational levels of the $f―$ state are found to be quasibound by an intrinaic berrier in its rotationiess potential energy curve and to predissociate. Absorptions into the $\Omega =5/2$ and $3/2$ substates produce a discrete spectrum from which the predissociation lifetimes of individual rotational levels can be determined. The $\Omega =1/2$ and $-1/2$ substates, however, dissociate so rapidly that absorptions into them appear only as an underlying continuum in the band spectrum. A three-level optical-optical double resonance technique is used to isolate individual rotational levels in these substates, allowing their absorption linewidths to be explicitly measured. This technique further allows transitions into the nonpredissociated $\upsilon -1$ levels of this state to be observed. The molecular constants and predissociation mechanisms of $f―4\Pi g$ will be discussed.