We present calculated cross sections and rate coefficients for the formation of the dicarbon cation ( \textrm { C } _ { 2 } ^ { + } ) by the radiative association process in collisions of a \textrm { C } ( ^ { 3 } P ) atom and a \textrm { C } ^ { + } ( ^ { 2 } P ^ { o } ) ion .
Molecular structure calculations for a number of low-lying doublet and quartet states of \textrm { C } _ { 2 } ^ { + } are used to obtain the potential energy surfaces and transition dipole moments coupling the states of interest , substantially increasing the available molecular data for \textrm { C } _ { 2 } ^ { + } .
Using a quantum-mechanical method , we explore a number of allowed transitions and determine those contributing to the radiative association process .
The calculations extend the available data for this process down to the temperature of 100 K , where the rate coefficient is found to be about 2 \times 10 ^ { -18 } \textrm { cm } ^ { 3 } / \textrm { s } .
We provide analytical fits suitable for incorporation into astrochemical reaction databases .