Nonlinear spectroscopy in astronomy: assignement of diffuse interstellar absorption bands to L(α) -induced, two-photon absorption by H2 molecules

All (twelve) optical diffuse interstellar absorption bands appearing in the interval 768.0–788.0 nm are assigned on the basis of a nonlinear effect: Lyman-alpha-driven, resonantly enhanced two-photon absorption by hydrogen molecules located near H II regions of young, hot stars.