ELECTRONIC SPECTROSCOPY AND ELECTRONIC STRUCTURE OF THE 3d TRANSITION METAL ALUMINIDES: AlCa, AlV, AlCr, AlMn, AlCo, AlNi, AlCu, AND AlZn
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Date
1994
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Ohio State University
Abstract
A systematic study of the chemical bonding between aluminum and the 3{d} series of transition metal atoms has been initiated using the technique of resonant two-photon ionization spectroscopy of the diatomic metals in a jet-cooled supersonic expansion. Rotationally resolved studies have led to the determination of $^{2}\Pi ^{5}\Pi_{b} ^{3}\Delta_{i}, ^{2}\Pi_{e}, ^{1}\Sigma^{+}$ and $^{2}\Pi$, ground states for AlCa, AlMn, AlCo, AlNi, AlCu, and AlZn, respectively. In addition, the observation of abrupt predissociation thresholds in the spectra of AlV, AlCr, AlCo, and AlNi, has permitted the bond strengths of these transition metal aluminides to be estimated. For the transition metals which readily adopt a $3a^{n+1} 4s^{1}$ configuration, strong bonds are found to result from the formation of a two electron $^{3}p\Sigma_{A1}-4s\Sigma$ bond. This leads to bond strengths and bond lengths of 1.844 eV and 2.38 {\AA} in AlCo; 2.29 eV and 2.32 {\AA} in AlNi; 2.32 eV and 2.34 {\AA} in AlCu; and a bond strength of 2.27 eV in AlCr. The transition metals which cannot readily adopt a $3a^{n+1} 4s^{1}$ configuration are found to bond via $3p\pi$ approach of the aluminum atom to the $3d^{0} 4s^{2}$ metal atom, resulting in much longer bond lengths of 3.15 {\AA} (AlCa). 2.70 {\AA} (AlMn), and 2.69 {\AA} (AIZn). These periodic trends will be discussed, and evidence will be presented for the existence of a $3p\pi_{a1}-3d\pi$ bonding interaction in the cases of AIMn and A1Co.
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Author Institution: Department of Chemistry, University of Utah