A variety of ab initio methods have been used to calculate the X̃Π2 and ÃΣ+2 state spectroscopic parameters of the GeCX(X=F,Cl,Br) free radicals. The theoretical methods and basis sets were tested on GeCH, for which extensive experimental data are available, and found to give predictions sufficiently reliable to guide experimental searches for spectra. In all cases, the linear GeCX species was found to be the global minimum on the potential energy surface, with the bent XGeC(A2) isomer as a local minimum much higher (6236kcalmol) in energy. In both the ground and excited states, the GeC moiety is very similar to that of GeCH, with a double bond in the lower state and a triple bond in the excited state, indicating that halogenation does not radically perturb the energetics or structure of germanium methylidyne. Ground state GeCX radicals have suitable rotational constants for microwave studies, although they suffer from only modest dipole moments. Matrix infrared experiments are most likely to detect the ν1 fundamentals in the 14501100cm1 region or the ν3 fundamentals at the transition between the mid- and far-infrared regions. We have used the ab initio values for the Renner-Teller parameter, the average bending frequency, and the spin-orbit coupling constant to calculate the ground state energy levels, which will be helpful in the interpretation of Ã-X̃ single vibronic level emission spectra, if they can be observed. The electronic absorption spectra of the Π322 spin component of the 000 bands of all three radicals have been calculated assuming typical jet-expansion conditions and should be useful in future laser-induced fluorescence, resonance enhanced multiphoton ionization, or cavity ringdown searches for the electronic band systems.

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