Electron Emission from Aligned Superexcited O* Atoms Produced in Photodissociation ofO2in the 22.20–22.36 eV Region

Photoelectron photoion coincidence and threshold photoelectron photoion coincidence time of flight spectra for $O_2$ molecules in the 22.20–22.36 eV region have been measured to investigate anisotropy in dissociative photoionization processes. Some of the ${\mathrm{O}}^{+}$ ions were produced in a particular photodissociation process in which the molecule fragments into an $\mathrm{O}\left({}_{}{}^3{}_{}{}^{}P\right)$ atom and an excited ${\mathrm{O}}^{*}\left[{}_{}{}^2{}_{}{}^{}P_{}^o{}_{}{}^{}{3d}^{\prime \prime }\right]$ atom, which autoionizes to produce ${\mathrm{O}}^{+}\left({}_{}{}^2{}_{}{}^{}D_{}^o{}_{}{}^{}\right){+e}^{-}\left(0.16\mathrm{eV}\right)$. The ${\mathrm{O}}^{+}$ spectra present a nonisotropic profile which is interpreted as the result of a photodissociation process producing aligned ${\mathrm{O}}^{*}$ atoms followed by ejection of an electron along the axis of the dissociating molecule.