Laboratory IR spectra of 4-azachrysene in solid H2O

We present the mid-IR spectrum of 4-azachrysene (C17H11N) frozen in solid H2O at 14 K, data directly comparable to astronomical observations along dense cloud lines of sight. We tabulate the positions, profiles, and relative intensities of those 4-azachrysene peaks not obscured by strong H2O absorptions and note some significant changes in position and/or intensity relative to the previously published values for 4-azachrysene isolated in an argon matrix. In contrast to simple PAHs that do not interact strongly with solid H2O, PANHs, with their nitrogen atom(s), are potentially capable of hydrogen bonding with H2O, and this presumably gives rise to some of the spectral changes. This demonstrates that observers will not always be able to rely on peak positions of matrix isolated PANHs to correctly reflect the actual absorption band positions of PANHs along lines of sight where they will exist as pure solids or be frozen in H2O. In general these nitrogen heterocycles are of astrobiological interest since this class of molecules has been detected in meteorites, they could be pre-biotically important, and/or they could act as false biomarkers.