Spectroscopic analysis of the open 3 d subshell transition metal aluminides: AIV, AICr, and AICo

Three open 3d subshell transition metal aluminides, AlV, AICr, and AlCo, have been investigated by resonant two-photon ionization spectroscopy to elucidate the chemical bonding in these diatomic molecules. The open nature of the 3d subshell results in a vast number of excited electronic states in these species, allowing bond strengths to be measured by the observation of abrupt predissociation thresholds in a congested optical spectrum, giving D?(AlV)=1.489?0.010 eV, D?(AlCr)=2.272?0.009 eV, and D?(AlCo)= 1.844?0.002 eV. At lower excitation energies the presence of discrete transitions has permitted determinations of the ground state symmetries and bond lengths of AlV and AlCo through rotationally resolved studies, giving r-6 (AlV, ??=O)=2.620?0.004 A and r: (AlCo, ??=3)=2.3833?0.0005 A. Ionization energies were also measured for all three species, yielding IE(AIV)=6.01?0.10 eV, IE(AlCr)=5.96?0.04 eV, and IE(AlCo)=6.99?0.17 eV. A discussion of these results is presented in the context of previous work on AlCu, AlNi, AlCa, and AlZn.