Fluorescent Line Emission of Molecular Hydrogen

Abstract

The electric quadrupole vibration-rotation transitions of molecular hydrogen can be excited either by thermal collisions in regions of high temperature or by ultraviolet absorption and fluorescence that leaves the molecules in excited levels, v>0, of the electronic ground state in interstellar clouds located very close to hot stars. Predictions of this fluorescent emission (Gould and Harwit 1963, Black and Dalgarno 1976) have only recently been confirmed by observations in Orion (Hayashi et al. 1985) and toward the reflection nebula NGC 2023 (Gatley and Kaifu 1987). Most previous observations of the 2 μm H2 lines have been consistent with thermal excitation in shocked regions.