Gas-phase Absorptions of near 8300 Å below 10 K: Astronomical Implications

Abstract

The gas-phase electronic spectrum of ( ) with an origin band at has been measured below by photofragmentation of helium complexes ( ) in a radiofrequency trap. is a medium-sized polycyclic aromatic hydrocarbon (PAH) cation, and using an ion trapping technique it has been possible to record a high-quality gas-phase spectrum to directly compare with astronomical observations. No diffuse interstellar bands (DIBs) have been reported at the wavelengths of the strongest absorption bands in the spectrum. Measurement of absolute absorption cross sections in the ion trap allows upper limits to the column density of this ion to be , indicating that even PAH cations of this size, which are believed to be stable in the interstellar medium, should be excluded as candidates for at least the strong DIBs.