ExoMol line lists XXXI: Spectroscopy of lowest eights electronic states of C${}_2$

Accurate line lists for the carbon dimer, C${}_2$, are presented. These line lists cover rovibronic transitions between the eight lowest electronic states: $X{}^1{\mathrm{\Sigma }}_g^{+}$, $a{}^3{\mathrm{\Pi }}_u$, $A{}^1{\mathrm{\Pi }}_u$, $b{}^3{\mathrm{\Sigma }}_g^{-}$, $b{}^3{\mathrm{\Sigma }}_g^{-}$, $c{}^3{\mathrm{\Sigma }}_u^{+}$, $d{}^3{\mathrm{\Pi }}_g$, $B{}^1{\mathrm{\Delta }}_g$, $B^{\mathrm{\prime }}{}^1{\mathrm{\Sigma }}_g^{+}$. Potential energy curves (PECs) and transition dipole moment curves are computed on a large grid of geometries using the aug-cc-pwCVQZ-DK/MRCI level of theory including core and core-valence correlations and scalar relativistic energy corrections. The same level of theory is used to compute spin-orbit and electronic angular momentum couplings. The PECs and couplings are refined by fitting to the empirical (MARVEL) energies of ${}^{12}$C${}_2$ using the nuclear-motion program Duo. The transition dipole moment curves are represented as analytical functions to reduce the numerical noise when computing transition line strengths. Partition functions, full line lists, Land'{e}-factors and lifetimes for three main isotopologues of C${}_2$ (${}^{12}$C${}_2$,${}^{13}$C${}_2$ and ${}^{12}$C${}^{13}$C) are made available in electronic form from the CDS (http://cdsarc.u-strasbg.fr) and ExoMol (www.exomol.com) databases.