Observational analysis of the well--correlated diffuse bands: 6196 and   6614 \AA
  We confirm, using spectra from seven observatories, that the diffuse bands 6196 and 6614 are very tightly correlated. However, their strength ratio is not constant as well as profile shapes. Apparently the two interstellar features do not react in unison to the varying physical conditions of different interstellar clouds. 
J. Krelowski, G.A. Galazutdinov, A. Bondar, Y. Beletsky
astro-ph.GA