Reactions of hydrogen atoms with fluorene (C13H10): Infrared spectra of 9H-fluoren-9-yl (C13H9) and monohydrofluorenyl (1H-, 2H-, 3H-, and 4H-C13H11) radicals isolated in solid para-hydrogen

Abstract

Fluorene (C₁₃H₁₀), a polycyclic aromatic hydrocarbon (PAH) identified in the Cold Bokkeveld meteorite, contains both five- and six-membered rings and is considered as a structural precursor to C₆₀. In this study, we report the formation of 9H-fluoren-9-yl (C₁₃H₉) and four isomers of monohydrofluorenyl radicals (1H-, 2H-, 3H-, and 4H-C₁₃H₁₁) via reactions of hydrogen atoms with fluorene in solid para-hydrogen (p-H₂) matrices. Ultraviolet/infrared (UV/IR) irradiation of a C₁₃H₁₀/Cl₂/p-H₂ matrix at 3.5 K generated H atoms, which subsequently reacted with fluorene via hydrogen-abstraction or hydrogen-addition pathways to produce these radicals. Newly observed IR absorption bands were categorized based on their secondary photolytic responses at 420 nm and 360 nm. Spectral assignments of observed features in each group were achieved by comparing experimental data with scaled harmonic vibrational wavenumbers and IR intensities predicted for C₁₃H₉, 1H-, 2H-, 3H-, and 4H-C₁₃H₁₁ radicals and other possible candidates using the B3LYP/6-311++G (d,p) method. The IR spectra of the four mono-hydrogenated fluorenes, 1H-, 2H-, 3H-, and 4H-C₁₃H₁₁, are previously unreported.