Photoelectron spectroscopy of nickel, palladium, and platinum oxide anions

The 364-nm negative ion photoelectron spectra of XO and OXO molecules (X = Ni, Pd, and Pt) are reported. The spectra yield the electron affinities (EAs): EA(NiO) = 1.455 +/- 0.005 eV; EA(PdO) = 1.672 +/- 0.005 eV; EA(PtO) = 2.172 +/- 0.005 eV; EA(ONiO) = 3.043 +/- 0.005 eV; EA(OPdO) = 3.086 +/- 0.005 eV; EA(OPtO) = 2.677 +/- 0.005 eV. In addition, for the diatomics, transitions from the anion (X) over tilde (2)Pi(3/2) and (X) over tilde (2)Pi(1/2) states into neutral (X) over tilde (3)Sigma(-), (3)Pi, and for NiO and PdO, (1)Pi, are assigned. Several states have been reassigned from those in the existing literature. Anion (2)Pi(3/2)-(2)Pi(1/2) spin-orbit splittings are measured, as are neutral (3)Pi(2)-(3)Pi(1) spin-orbit splittings: the XO (3)Pi(2)-(3)Pi(1) splittings increase from 405 +/- 30 cm(-1) (NiO) to 805 +/- 30 cm(-1) (PdO) to 3580 +/- 40 cm(-1) (PtO). A bond length shortening of 0.03 +/- 0.01 Angstrom is measured upon electron detachment from NiO-, resulting in an anion bond length of 1.66 +/- 0.01 Angstrom. The bond length does not change upon electron detachment from PdO- using 3.4-eV photons. The Pt-O bond length decreases by 0.035 +/- 0.010 Angstrom in the (3)Pi(1) <-- (2)Pi(3/2) transition. The spectrum of OPtO displays a significantly more extended vibrational progression than those of ONiO or OPdO, and the O-Pt bond length is found to decrease by 0.07 +/- 0.01 Angstrom upon electron detachment. The spectra support the view that the Ni-O bond is largely ionic, the Pd-O bond is somewhat less so, and the Pt-O bond displays a substantial covalent character. (C) 2002 Elsevier Science (USA).