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The optical spectrum of jet-cooled Ge2 has been observed for the first time. Laser-induced fluorescence (LIF) and wavelength resolved emission spectra were recorded using the pulsed discharge technique with a tetramethylgermane precursor. Analysis of the spectra yielded the vibrational constants ωe″=287.9(47), ωexe″=0.81(55), ωeye″=0.0037(18), ωe′=189.0(15), ωexe′=6.41(30), and Te′=20 610.8(16) cm−1. High-resolution rotationally resolved spectra of several bands of Ge274 show two strong P and R branches and two very weak Q branches. We have assigned the band system as a Hund’s case (c) Ω′=1−Ω″=1 transition from the ground Σg−3 state to a Σu−3 excited state. The bond lengths derived from the rotational constants are r0″=2.3680(1) Å and re′=2.5244(18) Å, an ∼0.16 Å increase on electronic excitation. Arguments are presented for assigning the transition to a σg2πu2→σg2πuπg electron promotion, although the observed increase in the bond length is much less than predicted by previous ab initio calculations. The absence of the 0u+–0g+ component in the spectra has been attributed to an excited state predissociation.

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