Diffuse band shifts: a possible explanation

We discuss the behaviour of broad and narrow diffuse interstellar bands ins ide the Orion association. The peculiarities, observed in this region, such as enormous weakness of some features as well as wavelength shifts of othe rs suggest that the diffuse band carriers - most probably some sort of comp lex molecules - accrete onto grain surfaces. It appears that the processes which occur upon accretion make the narrow DIBs vanish while the broader fe atures are less attenuated but always red-shifted. The observed shapes of i nterstellar extinction curves suggest that where this happens the small dus t grains which are responsible for the FUV extinction are also reduced in n umbers which naturally goes along with gas accretion and increased ratio of total to selective extinction.