The AlCO- and Al(CO)(2)(-) anions: Matrix isolation infrared spectra and density functional theory studies

After deposition of laser ablated aluminum with CO in excess argon at 11 K, distinct IR bands at 1682.3, 1803.9, and 1741.0 cm(-1) have been observed in addition to the absorptions of neutral AlCO and Al(CO)(2). With the aid of (CO)-C-13 isotope enriched experiments and density functional calculatio ns, the band at 1682.3 cm(-1) has been assigned to the C-O stretch vibratio n of the AlCO- anion. Absorptions at 1803.9 and 1741.0 cm(-1) have been ass igned to the symmetric and antisymmetric C-O stretching vibrations of the A l(CO)(2)(-) anion, respectively. Vertical detachment energies of AlCO- and Al(CO)(2)(-) as well as the electron affinities of AlCO and Al(CO)(2) have been calculated. The properties of MCO- anions (M=B, Ga, and In) have also been predicted for comparison with those of AlCO-. (C) 2000 American Instit ute of Physics. [S0021-9606(00)00846-1].