1. Introduction  
2. Observations and single-cloud target selection  
3. Interstellar  $\mathbf{C}_{2}$   lines: detection and analysis  
4. Extractions of the  $\mathbf{C}_{2}$  -DIBs  
5. Variability of profiles among the eighteen  $\mathtt{C}_{2}$  -DIBs  
6. Prominent sub-structures and average spectral profiles  
7. Search for profile variability among the sightlines  
8. Correlation studies  
9. Summary and conclusion