The gas phase optical spectrum of jet-cooled Pt2 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 Pt2 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 Pt2 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+2 as D0(Pt−Pt+)=3.26±0.24 eV. The strength of the chemical bond in Pt2, as compared to Au2, demonstrates that there are significant 5d contributions to the chemical bonding in Pt2.

Gas phase spectroscopic investigations of the jet-cooled aluminum trimer are reported using the technique of resonant two-photon ionization with mass spectrometric detection. A discrete band system in the 5200–6100 Å region is observed, consisting of an extended vibrational progression in a single vibrational mode. In addition, an apparent continuum absorption is observed which gradually grows in toward shorter wavelengths. The apparent continuum exhibits a long lifetime, 24–35 μs, which is most unusual and indicates that the continuum arises from spectral congestion and not lifetime broadening. At 19 378 cm−1 both the discrete and the continuum absorptions terminate abruptly, indicating the onset of dissociation above this energy. Although it is not certain that dissociation above this energy leads to ground electronic state Al2, this measurement nevertheless places an upper limit on D0(Al2–Al) of 2.40 eV.

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We have measured the cosmic ray spectrum above 10 17.2 eV using the two air fluorescence detectors of the High Resolution Fly's Eye observatory operating in monocular mode. We describe the detector, photo-tube and atmospheric calibrations, as well as the analysis techniques for the two detectors. We fit the spectrum to a model consisting of galactic and extra-galactic sources.

The reactivity of Nb clusters with nitrogen and deuterium was studied using a pulsed laser vporization source coupled to a fast flow reactor. The relative reactivity of the various clusters was determined by monitoring the depletion of the cluster ion signal as a function of reactant flow rate. A kinetic analysis of the chemisorption is given. The geometrical isomerism of the cluster ions and its relationship to reactivity is discussed.(AIP)