Spectroscopy and electronic structure of jet-cooled Al?

Resonant two-photon ionization spectroscopy has been used to study the jet-cooled Al? molecule. The ground state has been conclusively demonstrated to be of 3IIu symmetry, deriving from the ???rr?u electronic configuration. High resolution studies have established the bond length of the X?IIu state as re (X?IIu) = 2.701 ? 0.002 ?. The third-law estimate of the Al? bond strength has been reevaluated using the observed and calculated properties of the low-lying electronic states to give Do (Al?) = 1.34 ? 0.06 eV. In addition to the previously reported E 2 ??-g 2 ?X?IIu and F 3??-g ?X3IIu band systems, the E' 3?IIg ?X?IIu, F"-X, F'-X, G ?IIg ?X?IIu, H' ??-g ?X?IIU, and H??g ?X?IIu band systems have been observed for the first time. Bands of the G-X, H '-X, and H-X systems have been rotationally resolved and analyzed, providing rotational constants and electronic state symmetries for the upper states of these systems. A discussion of all of the experimentally known states of Al2 is presented, along with comparisons to previous experimental and theoretical work.