Possible molecular hydrogen formation mediated by the radical cations of anthracene and pyrene

✍ Scribed by Mutsumi Hirama; Toshimasa Ishida; Jun-Ichi Aihara

• Publisher: John Wiley and Sons
• Year: 2003
• Tongue: English
• Weight: 89 KB
• Volume: 24
• Category: Article
• ISSN: 0192-8651
• DOI: 10.1002/jcc.10290

✦ Synopsis

Abstract

Hydrogen molecules cannot be formed readily by the association of gaseous hydrogen atoms. Possible H~2~ formation mediated by the radical cations of typical polycyclic aromatic hydrocarbons (PAHs), anthracene and pyrene, was studied at the B3LYP/6‐31G** level of theory. We presumed that H~2~ is formed by way of two elementary reactions: the addition of an H atom to a PAH molecular cation, and the H abstraction from the resulting monohydro‐PAH cation (i.e., arenium ion) by a second H atom to yield H~2~. The first reaction takes place without any activation energy. The second reaction is also predicted to proceed along almost barrierless pathways, although it is far from being a typical ion–molecule reaction. There is a possibility that these reactions might constitute one of the mechanisms for H~2~ formation in extremely cold interstellar space. Deuterium enrichment in PAH cations is possibly accompanied by such H~2~ formation because deuteration lowers the energies of polyatomic PAH cations appreciably. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1378–1382, 2003