A Theory Attributing Optical Diffuse Interstellar Absorption Bands (DIBs), 'Unidentified Infrared' Emission Bands (UIBs), and Cloud Reddening to H2 Nonlinear Absorption

A theory is described which attributes the diffuse interstellar absorption bands (DIBs) to coherently driven two-photon absorption by H2 molecules present in sheet-like clouds located near hot stars. Results from three-level, nonlinear spectroscopy are used to argue that VUV photons from the star Impinging on the H2-containing cloud will be primarily absorbed in simultaneous two-photon (Raman-type) transitions, resulting in the build-up of coherent VUV Stokes-wave radiation in the 'plane' of the H2-containing cloud on the transitions [Cn &iff. XO; P(2) and P(3); n = 0-5] and on some of the transitions [Bn &iff. XO, P(2) and P(3)]. Via this in-plane VUV Stokes-wave radiation, parahydrogen molecules in the (XO, J = 2) level and orthohydrogen molecules in the (XO, J = 3) level are coherently excited to levels [Cn(&Pi.+ over u); J' = 1 and 2; n = 0-5] and [Bn, J' = 1 and 2], which thus serve as the intermediate states in resonantly-enhanced, coherently driven, two-photon adsorption. The DIBs result from visible light from the star being simultaneously absorbed in second step' transitions from the coherently excited (C,B)-state levels to various singlet gerade state levels.

By: Peter P. Sorokin and James H. Glownia

Published in: Astrophysical Journal, volume 473, (no 2), pages 2900-20 in 1996

Please obtain a copy of this paper from your local library. IBM cannot distribute this paper externally.

Questions about this service can be mailed to reports@us.ibm.com .