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Session 16 - Interstellar Grains, PAH's and the Interstellar Bands.
Display session, Monday, January 13
Metropolitan Ballroom,
A theoretical model for the diffuse interstellar bands (DIBs) based upon nonlinear absorption by H_2 molecules in thin clouds located 1-10 pc from O-type stars is presented. On the basis of this model, one can assign over 70 of the roughly 130 known sharp DIBs to H_2 transitions occuring from B- and C-state quantum levels to singlet-gerade-state quantum levels, all to within the tight error limits determined by astronomers. The basic nonlinear absorption mechanism is simultaneous two-photon (VUV + visible light) absorption occuring in a collisionless medium, with the VUV photons being extracted from the pool of nearly resonant photons trapped by elastic scattering within the cloud.
