Theory of radiative electron attachment to molecules: Benchmark study of CN−

We have developed an approach based on first principles to study the process of radiative electron attachment (REA) to linear molecules of astrophysical interest in collisions between the molecules and electrons at energies below 1 eV. The approach is based on accurate ab initio calculations of electronic bound and continuum states of the negative ion. The electronic continuum states are obtained with the complex-Kohn variational method. The benchmark calculation for the REA to the simplest negative ion CN${}^{\ensuremath{-}}$, which was recently observed in the interstellar medium, has produced a relatively low rate coefficient $\ensuremath{\alpha}(T)=7.3\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ cm${}^{3}/$s at $T=30$ K. Moreover, our results are shown to agree well with microscopic reversibility applied on a recent photodetachment experiment on CN${}^{\ensuremath{-}}$. Finally, the study confirms a previous assessment that the CN${}^{\ensuremath{-}}$ ion is unlikely be formed by REA in the interstellar medium.