Infrared spectrum of hydrogenated corannulene rim-HC20H10 isolated in solid para-hydrogen

Abstract

Hydrogenated polycyclic aromatic hydrocarbons have been proposed to be carriers of the interstellar unidentified infrared (UIR) emission bands and the catalysts for formation of H2; spectral characterizations of these species are hence important. We report the infrared (IR) spectrum of mono-hydrogenated corannulene (HC20H10) in solid para-hydrogen (p-H2). In experiments of electron bombardment of a mixture of corannulene and p-H2 during deposition of a matrix at 3.2 K, two groups of spectral lines increased with time during maintenance of the matrix in darkness after deposition. Lines in one group were assigned to the most stable isomer of hydrogenated corannulene, rim-HC20H10, according to the expected chemistry and a comparison with scaled harmonic vibrational wavenumbers and IR intensities predicted with the B3PW91/6-311++G(2d,2p) method.The lines in the other group do not agree with predicted spectra of other HC20H10 isomers and remain unassigned. Alternative hydrogenation was achieved with H-atoms produced photochemically in the infrared-induced reaction Cl + H2 (v = 1) → H + HCl in a Cl2/C20H10/p-H2 matrix. With this method, only lines attributable to rim-HC20H10 were observed, indicating that hydrogenation via a quantummechanical tunneling mechanism produces preferably the least-energy rim-HC20H10 regardless of similar barrier heights and widths for the formation of rim-HC20H10 and hub-HC20H10. The mechanisms of formation in both experiments are discussed. The bands near 3.3 and 3.4 µm of rim-HC20H10 agree with the UIR emission bands in position and relative intensity, but other bands do not match satisfactorily with the UIR bands.

“Broken-hearted” carbon bowl via electron shuttle reaction: energetics and electron coupling

“…Notably, the reported hydrogenation reactions of corannulene typically occurred under relatively harsh conditions (e.g., electron bombardment, alkyllithium reagents, or alkali metals), and even despite them, reactions typically led to hydrogenation of one or two rim C]C bonds without carbon-carbon bond cleavage. [51][52][53][54][55][56][57] Since the developed conditions (C 20 H 10 /TCNQ/Zn/HCl) required the presence of zinc, we also probed the Clemmensen reduction that uses zinc amalgam and concentrated hydrochloric acid. 58 Mass spectrometry and 1 H NMR spectroscopy studies of reaction products detected the presence of only pristine corannulene and did not detect any traces of corannulene hydrogenation.…”

Infrared spectra of protonated and hydrogenated corannulene (C20H10) and sumanene (C21H12) using matrix isolation in solid para-hydrogen – implications for the UIR bands

“…In addition, an alternate method to produce hydrogenated PAHs by UV and IR irradiation of C 20 H 10 /Cl 2 /p-H 2 also produced the most stable rim and the second most favorable hub isomer. (Sundararajan et al (2019)).…”

Successive Hydrogenation of SO and SO2 in Solid para-H2: Formation of Elusive Small Oxoacids of Sulfur

“…To generate SOS, we have applied H atom reactions in solid para -H 2 at 3.1 K. This method was established in the past decade by the groups of Anderson and Lee. It is taking advantage of the phenomenon of quantum diffusion that allows for the efficient movement of the H atoms through the matrix, facilitating H addition and abstraction reactions. − Earlier studies in para -H 2 reported the successful hydrogenation of polycyclic aromatic hydrocarbons (PAHs), − HONO, isoprene, propene, and pyrrole . Hydrogen abstraction from the isolated molecule by the H atoms could also be detected recently in the case of formamide, methyl formate, and acetamide. − As it was shown by these studies, even if a H addition or a H abstraction reaction has a substantial barrier, it can be fast enough at very low temperatures due to H atom tunneling to observe it on the laboratory time scale.…”