Ab initio predictions of the spectroscopic parameters of the germanium halomethylidyne (Ge=C-X; X=F, Cl, Br) free radicals

Ab initio methods have been used to predict the spectroscopic parameters for the X˜2Πi and A˜2Σ+ states of the unknown germanium halomethylidyne (GeCX, X=F, Cl, Br) free radicals. The predictive powers of the chosen ab initio methods have been tested on the known GeCH radical. The calculations show the linear GeCX (X=F, Cl, Br) isomer is the global minimum on the potential energy surface, with the cyclic XGeC isomer being between 6400 (BrGeC) and 11300 (FGeC) cm−1 higher in energy. The ground state geometries, vibrational frequencies, spin-orbit coupling and Renner parameters have been calculated using the cc-pVTZ basis set. The excited state geometries, vibrational frequencies and excitation energies have also been calculated, and the rotational contours of the 000 bands have been simulated at medium resolution under jet-cooled conditions. These calculations will aid in the search of these unknown radicals.