THE C4H RADICAL AND THE DIFFUSE INTERSTELLAR BANDS - AN AB-INITIO STUDY

The electronic transitions of the C4H radical are investigated using correlated ab initio methods. The 0-0 bands are predicted to occur at 2484, 3884, and 3869 angstrom for the C2SIGMA+-X2SIGMA+, B2PI-X2SIGMA+, and B2PI-A2PI transitions, respectively. These results suggest that the strong 4428 angstrom diffuse interstellar band is not carried by C4H. The wavelengths of the strong, parallel (2PI-2PI) transitions from the ground states of C6H, C8H, C10H, and C12H are predicted to be 4798, 5834, 6906, and 7993 angstrom, using a simple semiempirical model. Comparison of these data with observed wavelengths adds support to the thesis that long carbon chains are carriers of diffuse interstellar bands.