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A multiwavelength study of laboratory carbons with varying degrees ofhydrogenation and sp$^2$ hybridization is required to characterize thestructure of the carbonaceous carriers of interstellar and circumstellarextinction. Analogs to carbonaceous interstellar dust encountered in variousphases of the interstellar medium have been prepared in the laboratory. Thinfilms have been measured in transmission in the vacuum ultraviolet (VUV; 120 -210 nm) within the atmospheric pressure experiment (APEX) chamber of the DISCObeam line at the SOLEIL synchrotron radiation facility. Spectra of these filmswere further measured through the UV-Vis (210 nm - 1 $\mu$m) and in themid-infrared (3 - 15 $\mu$m). Tauc optical gaps, E$_g$, are derived from thevisible spectra. The major spectral features are fitted through the VUV to themid infrared to obtain positions, full-widths at half maximum (FWHM), andintegrated intensities. These are plotted against the position of the$\pi$-$\pi^*$ electronic transitions peak. Unidentified or overlapping featuresin the UV are identified by correlations with complementary infrared data. Acorrelation between the optical gap and position of the $\pi$-$\pi^*$electronic transitions peak is found. The latter is also correlated to theposition of the sp$^3$ carbon defect band at ~8 $\mu$m, the aromatic C=Cstretching mode position at ~6 $\mu$m, and the H/C ratio. Our study suggeststhat carriers of the interstellar UV bump should exhibit infrared bands akin tothe A/B classes of the aromatic infrared bands, while the circumstellar bumpcarriers should exhibit bands corresponding to the B/C classes.

Polyaromatic disordered carbon grains as carriers of the UV bump: FUV to mid-infrared spectroscopy of laboratory analogs