A new spectrum associated with diatomic carbon

Abstract

A new system of very simple Σ–Σ bands in the region 4800–6000 Å has been observed in flash discharges in CH4, both in absorption and emission. The rotational analysis shows conclusively that the molecule responsible is a diatomic molecule containing two carbon nuclei, a conclusion that is further confirmed by the observation of the corresponding system using 13CH4 instead of 12CH4. Neither the upper nor the lower state is one of the known states of C2. None of the predicted low-lying states of C2 fits the observed new states. Two possibilities remain: either the new system corresponds to two fairly highly excited levels of C2 or it is due to the C2− ion. The latter alternative finds some support in the similarity of the new system to the near ultraviolet bands of N2+ (which has the same number of electrons). However, the doublet splitting required by this interpretation has not been resolved, nor has the study of perturbations in the upper state given clear-cut evidence for doublet structure. On the other hand, a mass-spectrometric investigation of the ions in the flash discharge producing the spectrum shows a strong C2− peak, while C2+ is weak. A definitive answer to the question of the carrier of the new spectrum cannot yet be given.