The data for each of eight isotopologues of C_2_ are in two parts. The first, s*.dat contain lists of rovibronic states. Each state is labelled with the total angular momentum, state degeneracy, Zeeman Lande-g factor, total (+/-) and e/f parities, vibrational quantum number, projection of the electronic, spin and total angular momenta. Each state has a unique number, which is the number of the row in which it appears in the file. This number is the means by which the state is related to the second part of the data system, the transitions files. Where available, the theoretical state energies computed using the Duo program (d) were replaced by experimentally derived energies using the MARVEL procedure (m). The transition files t*.dat contain four columns: the reference number in the energy file of the upper state; that of the lower state; the Einstein A coefficient of the transition; the transition wavenumber. The p*.dat files contain partition functions on a grid of 1K. ExoMol uses the HITRAN convention, where the nuclear statistical weights are included in the partition function as the corresponding functors.

S.N. Yurchenko, s.yurchenko(at)ucl.ac.uk J. Tennyson, j.tennyson(at)ucl.ac.uk