A THEORY ATTRIBUTING OPTICAL DIFFUSE INTERSTELLAR ABSORPTION BANDS, 'UNIDENTIFIED INFRARED' EMISSION BANDS, AND CLOUD REDDENING TO H_2 NONLINEAR ABSORPTION

摘要

A theory is described that attributes the diffuse interstellar absorption bands (DIBs) to coherently driven two-photon absorption by H_2 molecules present in sheetlike clouds located near hot stars. Results from three-level nonlinear spectroscopy are used to argue that vacuum ultraviolet (VUV) photons from the star impinging on the H_2-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 H_2-containing cloud on the transitions [Cn<=>X0; P(2) and P(3); n = 0-5] and on some of the transitions [Bn<=>X0, P(2) and P(3)]. Via this in-plane VUV Stokes-wave radiation, para-hydrogen molecules in the (X0, J″ = 2) level and ortho-hydrogen molecules in the (X0, J″ = 3) level are coherently excited to levels [Cn(∏_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 absorption. 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.