Exploring the Bermuda triangle of homonuclear diatomic spectroscopy: The electronic spectrum and structure of Ge2

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 74Ge2 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 3Σg− state to a 3Σu− excited state. The bond lengths derived from the rotational constants are r0″=2.3680(1) A and re′=2.5244(18) A, an ∼0.16 A 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 ...