Resonant two-photon ionization spectroscopy has been used to study the jet-cooled Al2 molecule. The ground state has been conclusively demonstrated to be of 3Πu symmetry, deriving from the σ1gπ1u electronic configuration. High resolution studies have established the bond length of the X3Πu state as re(X3Πu) =2.701±0.002 Å. The third-law estimate of the Al2 bond strength has been reevaluated using the observed and calculated properties of the low-lying electronic states to give D00 (Al2)=1.34±0.06 eV. In addition to the previously reported E 2 3Σ−g←X3Πu and F 33Σ−g←X3Πu band systems, the E′ 33Πg←X 3Πu, F″–X, F′–X, G 3Πg←X 3Πu, H′ 3Σ−g←X 3Πu, and H3Δg←X3Πu band systems have been observed for the first time. Bands of the G–X, H′–X, and H–X systems have been rotationally resolved and analyzed, providing rotational constants and electronic state symmetries for the upper states of these systems. A discussion of all of the experimentally known states of Al2 is presented, along with comparisons to previous experimental and theoretical work.

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.

An optical spectrum, obtained by resonant two-photon ionization spectroscopy, is reported for jet-cooled diatomic gallium arsenide. The ground state is identified as X 3Σ−, deriving from a σ2π2 molecular configuration, and is characterized by ω″e=215 cm−1, ω″ex″e=3 cm−1, and r″0=2.53±0.02 Å. The upper state of the observed band system is 3Πr correlating to the Ga 4s24p, 2P0+As 4s24p3, 2D0 excited separated atom limit. A strong predissociation sets in above v′=0 for the Ω′=2,1 and 0− components of the 3Πr excited state, and it is proposed that this is induced by spin–orbit interaction with the σσ*π2, 5Σ− state which correlates to ground state atomic fragments. Constants for the upper 3Π0+ state are ω′e=152.13±0.70 cm−1, ωex′e=2.89±0.08 cm−1, and re=2.662±0.027 Å for the 69Ga75As isotopic modification. The ionization potential of GaAs has been bracketed as IP(GaAs)=7.17±0.75 eV, and a re-evaluation of the third-law measurement of the bond strength provides D0(GaAs)=2.06±0.05 eV. Comparisons to group IV and other group III-V diatomics, and to the bulk solid materials are also presented.

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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