FLUORESCENT MOLECULAR-HYDROGEN LINE EMISSION IN THE FAR-RED

Over 30 lines from the nu = 3-0, 4-1, 7-3 and 8-4 vibrational series of the hydrogen molecule have been observed from lambda = 7600-8800 angstrom in the reflection nebula NGC 2023, originating from levels up to 41 000 K above ground. This is the first time that H-2 has been observed in the optical CCD regime and these are the highest excitation lines from the ground electronic state that have yet been detected. The spectrum shows the characteristics expected of UV fluorescence, although in detail there are some differences from model predictions. Emission from newly formed molecules in nu = 4 may have been detected. Strong [C I] 8727-angstrom forbidden line emission is also observed, coincident with the H-2 emission, and arising from the same photodissociation region gas.