The 3.49 eV photoelectron spectra of HNiCO-, PdCO-, and PtCO- generated from the gas-phase reaction of atomic anions with methanol are presented and interpreted in the context of new density functional calculations. The calculated electron affinities (EAs) for PdCO (0.58 eV) and PtCO (1.13 eV) are in excellent agreement with experimental values [0.606(10) and 1.212(10) eV, respectively] while for HNiCO, the calculated EA (1.64 eV) is 0.48 eV lower than the experimental value. However, in all three cases, the vibrational frequencies and spectral profiles are consistent with calculated structures, frequencies, and normal coordinates. HNiCO- and HNiCO are predicted to be linear, with (1)Sigma(+) and (2)Delta ground states, respectively. Calculations on PdCO- agree with recent calculations by Andrews and co-workers [J. Phys. Chem. A 104, 3905 (2000)] which predict a bent (2)A' ground state. The ground state of PtCO- is calculated to be the linear (2)Sigma(+) state. Both PdCO and PtCO are predicted to have (1)Sigma(+) ground states. For all species, backdonation of d(pi)-electron density into the CO pi* orbital is an important component of the metal carbonyl bond, with the effect being more pronounced in the anions. (C) 2003 American Institute of Physics.