HYDROGENATED POLYCYCLIC AROMATIC-HYDROCARBONS AND THE 2940-WAVE-NUMBER AND 2850-WAVE-NUMBER (3.40 AND 3.51 MICRON) INFRARED-EMISSION FEATURES

The 3150-2700 cm(-1) (3.17-3.70 mu m) range of the spectra of a number of Ar-matrix-isolated PAHs containing excess H atoms (H-n-PAHs) are p resented. This region covers features produced by aromatic and aliphat ic C-H stretching vibrations as well as overtone and combination bands involving lower lying fundamentals. The aliphatic C-H stretches in mo lecules of this type having low to modest excess H coverage provide ex cellent fits to a number of the weak emission features superposed on t he plateau between 3080 and 2700 cm(-1) (3.25 and 3.7 mu m) in the spe ctra of many planetary nebulae, reflection nebulae, and H II regions. Higher H coverage is implied for a few objects. We compare these resul ts in context with the other suggested identifications of the emission features in the 2950-2700 cm(-1) (3.39-3.70 mu m) region and briefly discuss their astrophysical implications.