Peripherally hydrogenated neutral polycyclic aromatic hydrocarbons as carriers of the 3 micron interstellar infrared emission complex: results from single-photon infrared emission spectroscopy. The Astrophysical journal. [Astrophys J] Journal article

Infrared emission spectra of five gas-phase UV laser-excited polycyclic aromatic hydrocarbons (PAHs) containing aliphatic hydrogens are compared with the main 3.3 microns and associated interstellar unidentified infrared emission bands (UIRs). We show that neutral PAHs can account for the majority of the 3 microns emission complex while making little contribution to the other UIR bands; peripherally hydrogenated PAHs produce a better match to astrophysical data than do those containing methyl side groups; 3.4 microns plateau emission is shown to be a general spectral feature of vibrationally excited PAHs containing aliphatic hydrogens, especially those containing methyl groups; and finally, hot-band and overtone emissions arising from aromatic C-H vibrations are not observed in laboratory emission spectra, and therefore, in contrast to current assignments, are not expected to be observed in the UIRs.

The Astrophysical journal. [Astrophys J]

Astronomy
Carbon
Comparative Study
Exobiology
Extraterrestrial Environment
Hydrogen
Hydrogenation
Lasers
Methylation
Polycyclic Hydrocarbons, Aromatic
Research Support, Non-U.S. Gov't
Research Support, U.S. Gov't, Non-P.H.S.
Spectrophotometry, Infrared