N-dependence of the reaction rate for C++C/sub n/→C+/sub n/+1 in the interstellar space

The rate of the radiative association reaction C+→C/sub n/→C+/sub n/+1 +hν is considered under the conditions in interstellar space. The lifetimes of the energized C+/sub n/+1 ion are estimated from the Rice-Ramsperger-Kassel-Marcus (RRKM) model of unimolecular decomposition and compared with the lifetime of infrared emission. It is shown that this reaction proceeds efficiently with the Langevin rate for n> or =4. Thus, the carbon chain can grow very quickly once it reaches C4. This may explain the observed abundance of long carbon chain molecules in interstellar space