Spectroscopy and electronic structure of jet-cooled NiPd and PdPt

Resonant two-photon ionization spectroscopy of jet-cooled NiPd and PdPt has revealed a dense vibronic spectrum for NiPd and a much more sparse spectrum for PdPt. Four vibrational progressions have been identified for NiPd, and three have been located for PdPt. High resolution investigations of NiPd have established a ground state bond length of r"o = 2.242 ? 0.005 ? with ?"= 2. The observed spectra have been used to bracket the ionization potentials, giving IP(NiPd) = 7.18 ? 0.76 eV and IP(PdPt) = 8.27 ? 0.38 eV. In contrast to previous work on Ni2 , NiPt, and Pt2 , no abrupt onset of rapid predissociation is observed for either NiPd or PdPt. A discussion of this result in terms of the expected potential energy curves for the palladium-containing diatomics is presented, which when combined with the frequencies of the highest energy vibronic bands observed yields estimates of D0(NiPd)~1.46 eV and D0(PdPt)~1.98 eV. The lack of observable vibronic transitions in Pd? above 11 375 cm-1 places D0(Pd?) below 1.41 eV, in agreement with Knudsen effusion mass spectrometry. Finally a comparison of the platinum group dimers and the coinage metal dimers is given, demonstrating the increasing importance of (/-orbital contributions to the bonding in the platinum group dimers as one moves down the periodic table. The anomalous behavior of the palladium-containing diatomics is also discussed in terms of the highly stable 4d10 5s?, ?S0 ground state of atomic palladium.