Ab initio characterization of the aluminum dimer in its X and A electronic states

The potential energy functions of the aluminum dimer, Al₂ , in its lowest-energy electronic states, X $$ and A $$ have been determined from ab initio calculations using the multi-reference averaged coupled-pair functional method in conjunction with the correlation-consistent basis sets up to septuple-zeta quality. The core-electron correlation, scalar relativistic, and spin-orbit effects were taken into account. The vibration-rotation energy levels for both the states of Al₂ were calculated to near the "spectroscopic" accuracy. The $$ state was unequivocally confirmed to be the electronic ground state of Al₂ , and the electronic term value $$ of the $$ state was predicted to be 247 cm^-1 . The energies and intensities of direct electronic-vibration transitions X $$  ↔ A $$ were predicted.