EXPERIMENTAL AND THEORETICAL EVIDENCE FOR A NEW METASTABLE VALENCE STATE OF O2

A new metastable state of O2 has been observed following the charge exchange of fast beaMS Of O2+ with alkali metals. Coupling of the experimental results with ab initio calculations provides strong arguments for the identification of the metastable as the previously unknown 1(1)DELTA(u) valence state which adiabatically dissociates to O(1D) + O(1D). The primary relaxation pathway is found to be a spin-orbit induced predissociation by the repulsive 2(3)DELTA(u) state for which an H(SO) = 9 (+/-1) cm-1 matrix element is determined. Due to accidentally small Franck-Condon factors the v = 2 level of the 1(1)DELTA(u) state is particularly long-lived and evidences extraordinarily large isotope effects with the lifetime for this level being 0. 1, 1.8, and 0.5 mus for O-32(2), O-34(2), and O-36(2) respectively. The other low vibrational levels of the 1(1)DELTA(u) state are predicted to have lifetimes of approximately 5-1 0 ns, suggesting that high-quality spectra of these states should be obtainable and that chemical reactions of this new state Of O2 are possible.