Current status of the H2 diffuse interstellar bands theory Assignments of the λλ5780, 6284, 4428, 4882 large-equivalent-width diffuse interstellar bands

Abstract

Major changes recently incorporated into the structure of the non-linear H₂ DIBs model (P. P. Sorokin and J. H. Glownia, AstrophysJ., 1996, 473, 900) are outlined. To account for observed relative intensities of narrow DIBs assigned in the original model to H₂ inter-Rydberg transitions, it has become necessary to postulate a form of lightwave coherence existing in the H₂-containing cloud of the model, with numerous coherent 2n wave-mixing processes, each initiated by broadband stimulated Raman scattering (SRS), occurring on various H₂ transitions. By considering such wave-mixing processes, it becomes possible both to interpret archived VUV spectra of B-type supergiants and to easily assign large-equivalent-width DIBs (e.g. λλ5780, 6284, 4428, 4882) whose origins cannot be understood using the original ‘passive’ H₂ two-photon absorption model. The wave-mixing schemes discussed also enable one to understand why DIB intensities in given lines-of-sight correlate well with the amount of reddening observed in the same lines-of-sight.