A LOW-LYING EXCITED ELECTRONIC STATE OF AIO MOLECULE AND GROUND-STATE DISSOCIATION ENERGY

Emission bands near 2500 and 2800 Å, from a microwave discharge through gaseous AlCl3 and O2, have been found to have a common lower 2Πi state. Rotational analysis of the 0-0 band of the 2800 Å system, and also the vibrational analysis, show that the system originates from the 2Σ+ state at 40 300 cm-1 and terminates in the previously unrecognized 2Πi state at 5300 cm-1. In the 2500 Å system the upper state is found to be a 2Δi state from the rotational analysis. The constants obtained for the new states are (cm-1): {A table is presented}. Establishment of the low-lying Π-state allows a reinterpretation of a continuum observed by Tyte, which gives an upper limit to the ground-state dissociation energy of 5.2 eV. This, in turn, suggests that the B2Σ+ state (at 2.5 eV) dissociates into ions (Al+ + 0-) 4.5 eV above the lowest free-atom energy. © 1969.