Resonant two-photon ionization spectroscopy of jet-cooled Pt?

The gas phase optical spectrum of jet-cooled Pt? has been investigated over the range of 11 300 to 26 300 cm -1 using resonant two-photon ionization spectroscopy in combination with time-of-flight mass spectrometry. Numerous vibronic bands are observed. Analysis of the data gives the location of some 26 excited electronic states, which are characterized by the frequencies of their origin bands, vibrational frequencies, and anharmonicities. Variation of the second color in a two-color resonant two-photon ionization scheme has determined the ionization threshold of Pt? to be 8.68 ?0.02 eV. The observation of the onset of predissociation, characterized by a sharp drop in excited state lifetime, places the dissociation energy of Pt? at 3.14?0.02 eV. In combination with the Pt atomic ionization potential of 8.8?0.2 eV, these results give the bond strength of Pt?+ as D0(Pt--Pt+) = 3.26 ? 0.24 eV. The strength of the chemical bond in Pt?, as compared to Au?, demonstrates that there are significant 5d contributions to the chemical bonding in Pt?.