Formation of H2 from internally heated polycyclic aromatic hydrocarbons: excitation energy dependence

T Chen; M Gatchell; M H Stockett; R Delaunay; A Domaracka; E R Micelotta; A G G M Tielens; P Rousseau; L Adoui; B A Huber; H T Schmidt; H Cederquist; H Zettergren

doi:10.1063/1.4917021

Formation of H2 from internally heated polycyclic aromatic hydrocarbons: excitation energy dependence

J Chem Phys. 2015 Apr 14;142(14):144305. doi: 10.1063/1.4917021.

Authors

T Chen¹, M Gatchell¹, M H Stockett¹, R Delaunay², A Domaracka², E R Micelotta³, A G G M Tielens⁴, P Rousseau², L Adoui², B A Huber², H T Schmidt¹, H Cederquist¹, H Zettergren¹

Affiliations

¹ Department of Physics, Stockholm University, S-106 91 Stockholm, Sweden.
² CIMAP, UMR 6252, CEA/CNRS/ENSICAEN/Université de Caen Basse-Normandie, bd Henri Becquerel, BP 5133, F-14070 Caen cedex 05, France.
³ Université Paris Sud, Institut d'Astrophysique Spatiale, UMR 8617, 91405 Orsay, France.
⁴ Leiden Observatory, Leiden University, P.O. Box 9513, 2300 RA Leiden, The Netherlands.

PMID: 25877576
DOI: 10.1063/1.4917021

Abstract

We have investigated the effectiveness of molecular hydrogen (H2) formation from Polycyclic Aromatic Hydrocarbons (PAHs) which are internally heated by collisions with keV ions. The present and earlier experimental results are analyzed in view of molecular structure calculations and a simple collision model. We estimate that H2 formation becomes important for internal PAH temperatures exceeding about 2200 K, regardless of the PAH size and the excitation agent. This suggests that keV ions may effectively induce such reactions, while they are unlikely due to, e.g., absorption of single photons with energies below the Lyman limit. The present analysis also suggests that H2 emission is correlated with multi-fragmentation processes, which means that the [PAH-2H](+) peak intensities in the mass spectra may not be used for estimating H2-formation rates.