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

Abstract

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 ${\mathrm{Al(CO)}}_{\mathrm{2}}.$ With the aid of ${}^{\mathrm{13}}\mathrm{CO}$ isotope enriched experiments and density functional calculations, the band at 1682.3 cm⁻¹ has been assigned to the C–O stretch vibration of the ${\mathrm{AlCO}}^{\mathrm{-}}$ anion. Absorptions at 1803.9 and 1741.0 cm⁻¹ have been assigned to the symmetric and antisymmetric C–O stretching vibrations of the ${\mathrm{Al(CO)}}_{\mathrm{2}}^{\mathrm{-}}$ anion, respectively. Vertical detachment energies of ${\mathrm{AlCO}}^{\mathrm{-}}$ and ${\mathrm{Al(CO)}}_{\mathrm{2}}^{\mathrm{-}}$ as well as the electron affinities of AlCO and ${\mathrm{Al(CO)}}_{\mathrm{2}}$ have been calculated. The properties of ${\mathrm{MCO}}^{\mathrm{-}}$ anions $(\mathrm{M=B},$ Ga, and In) have also been predicted for comparison with those of ${\mathrm{AlCO}}^{\mathrm{-}}.$