Infrared spectra of ovalene (C32H14) and hydrogenated ovalene (C32H15˙) in solid para-hydrogen.

We report the infrared (IR) spectra of ovalene (C32H14) and hydrogenated ovalene (C32H15˙) in solid para-hydrogen (p-H2). The hydrogenated ovalene and protonated ovalene were generated from electron bombardment of a mixture of ovalene and p-H2 during deposition of a matrix at 3.2 K. The features that decreased with time have been previously assigned to 7-C32H15+, the most stable isomer of protonated ovalene (Astrophys. J., 2016, 825, 96). The spectral features that increased with time are assigned to the most stable isomer of hydrogenated ovalene (7-C32H15˙) based on the expected chemistry and on a comparison with the vibrational wavenumbers and IR intensities predicted by the B3PW91/6-311++G(2d,2p) method. The mechanism of formation of 7-C32H15˙ is discussed according to the observed changes in intensity and calculated energetics of possible reactions of H + C32H14 and isomerization of C32H15˙. The formation of 7-C32H15˙ is dominated by the reaction H + C32H14 → 7-C32H15˙, implying that, regardless of the presence of a barrier, the hydrogenation of polycyclic aromatic hydrocarbons occurs even at 3.2 K.