H₂ catalysis through superhydrogenation of interstellar polycyclic aromatic hydrocarbons

Abstract

Experimental data showing superhydrogenation of neutral polycyclic aromatic hydrocarbons (PAHs) coronene, pentacene and pentacenequinone is presented. PAH monolayers were prepared on a highly oriented pyrolytic graphite surface and subsequently exposed to a beam of atomic hydrogen. The superhydrogenated PAH species were examined via temperature programmed desorption measurements. Stable intermediate superhydrogenation degrees as well as fully superhydrogenated species are observed and the initial reaction cross section for coronene has been determined.

Statistical vibrational autodetachment and radiative cooling rates of para-benzoquinone

“…The cumulative sum along the time dimension of the simulated g(E x , t) gives the fractions of the population above/ below E x , which is plotted in the inset. These sums, which are symmetric by construction, transform with an exponential time constant of 0.206 (7) s, which closely matches the experimental lifetimes determined from W 0 and W 1 , 0.19 (2) s. This supports our identification of the NMF-factorised component spectra with those of hot/cold ions with vibrational energies above/ below E x . The difference in the relative amplitudes between experiment and simulation may be attributable to differing absorption probabilities for the hot and cold ions.…”

“…6, which includes only wavelength region longer than 500 nm where hot-bands contribute most exclusively. According to the NMF analysis, nearly all the time variation in this wavelength region is due to the diminution of the hot component H 1 with a time constant of 0.16(3) s, while the cold component H 0 rapidly increases to a plateau with a time constant of 0.03(7) s. For comparison, single exponential fits of the time series at each wavelength give lifetimes increasing monotonically from 0.066 (11) s at 555 nm to 0.5(2) s at 505 nm, with a variance-weighted average lifetime of 0.130 (7) s. Here, the NMF reconstruction accounts for about 73% of the experimental variation, but the uncertainty in the components is larger than the previous spectrum (Fig. 4) as a wider range of solutions reproduce the relatively soft features in Fig.…”

“…5,6 Quinones may also play a role in the chemistry of interstellar clouds. 7,8 For example, irradiation of Polycyclic Aromatic Hydrocarbons (PAHs) in cosmic ice analogs is known to efficiently produce quinone-functionalised species in laboratory experiments. [9][10][11][12][13][14] In dark interstellar clouds, where functionalised aromatic molecules have been recently observed, 15,16 molecular anions are thought to be the dominant carriers of negative charge.…”