Searching for the Shortest-wavelength Aromatic Infrared Bands: No Evidence for the Predicted 1.05um Polycyclic Aromatic Hydrocarbon Feature

Polycyclic aromatic hydrocarbons (PAHs) are responsible for a variety of near- and mid-infrared spectral features in Galactic and extragalactic sources. A feature at 1.05 um arising from electronic transitions in PAH cations is predicted by laboratory experiments but has never been observationally confirmed. We conduct a dedicated search for this feature in absorption on a highly-extinguished sight line toward BD+40 4223, a blue supergiant in Cyg OB2, using the TripleSpec spectrograph at Palomar Observatory. We place a 5\sigma upper limit on the feature strength of $\Delta\tau/A_V < 5.6 \times10^{-3}$, ruling out theoretical estimates with $> 10\sigma$~significance.We constrain the effective temperature of BD+40~4223 to be $\log_{10}\left(T_{\rm eff}\right)=4.41\pm0.03$ and infer that it is veiled by $6.39\pm0.05$ magnitudes of visual extinction, consistent with but more constraining than previous determinations.As dust on the sight line toward BD+40 4223 appears typical of the diffuse interstellar medium, this non-detection challenges existing models of PAH material properties and/or charge distribution.