Universität zu Köln

Wenzel, Gabi ORCID: 0000-0002-0332-2641, Simon, Aude ORCID: 0000-0002-2315-9490, Banhatti, Shreyak ORCID: 0000-0002-5115-8671, Jusko, Pavol, Schlemmer, Stephan, Bruenken, Sandra and Joblin, Christine ORCID: 0000-0003-1561-6118 (2022). Infrared spectroscopy of the benzylium-like (and tropylium-like) isomers formed in the -H dissociative ionization of methylated PAHs. J. Mol. Spectrosc., 385. SAN DIEGO: ACADEMIC PRESS INC ELSEVIER SCIENCE. ISSN 1096-083X

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Abstract

Cationic benzylium and tropylium are known to be two competitive isomers for the -H fragment of the methylbenzene (toluene) cation. Methylated polycyclic aromatic hydrocarbon (PAH) cations are expected to be abundant in space and their dehydrogenation could lead to the formation of both the benzyliumand tropyliumlike cations, which are expected to be the two lowest-energy isomers. Here, we considered 1-methylpyrene and two less compact acene-substituted species, namely 2-methylnaphthalene and 2-methylanthracene, as precursors. The cationic -H fragments, C17H11+, C11H9+, and C15H11+, were produced by dissociative ionization, and their neon tagged complexes were formed in the 22-pole cryogenic ion trap instrument FELion that is coupled to the FELIX free electron laser. Infrared (IR) predissociation spectroscopy was performed showing that the strongest depletion band is located at about 1620 cm(-1), which reveals the predominance of the benzyliumlike, XCH2+, isomers, where X = Pyr, Nap, or Ant. Saturation depletion measurements showed that only this isomer is present in the case of C17H11+, whereas for the acene-derived species at least two are present with a large abundance. Synthetic spectra were generated from the theoretical anharmonic IR spectra of the two lowest-energy isomers, namely XCH2+ and the tropylium-like isomers, XC7+. Spectral comparison led us to conclude that there is no evidence for PyrC(7)(+) but clear evidence for NapC(7)(+). No specific spectral features could be identified for AntC(7)(+) due to a high spectral congestion. These results support the important role of PAH compactness in preventing the formation of XC7+ species. They also reveal the potential of XCH(2)(+ )species to account for the aromatic infrared band observed in emission at 6.2 mu m in astrophysical environments.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Wenzel, Gabi UNSPECIFIED orcid.org/0000-0002-0332-2641 UNSPECIFIED Simon, Aude UNSPECIFIED orcid.org/0000-0002-2315-9490 UNSPECIFIED Banhatti, Shreyak UNSPECIFIED orcid.org/0000-0002-5115-8671 UNSPECIFIED Jusko, Pavol UNSPECIFIED UNSPECIFIED UNSPECIFIED Schlemmer, Stephan UNSPECIFIED UNSPECIFIED UNSPECIFIED Bruenken, Sandra UNSPECIFIED UNSPECIFIED UNSPECIFIED Joblin, Christine UNSPECIFIED orcid.org/0000-0003-1561-6118 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-686980
DOI:	10.1016/j.jms.2022.111620
Journal or Publication Title:	J. Mol. Spectrosc.
Volume:	385
Date:	2022
Publisher:	ACADEMIC PRESS INC ELSEVIER SCIENCE
Place of Publication:	SAN DIEGO
ISSN:	1096-083X
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language POLYCYCLIC AROMATIC-HYDROCARBONS; MICRON EMISSION; SPECTRUM; COMPLEXES; DYNAMICS; BENZENE; TOLUENE; PYRENE; IONS Multiple languages Physics, Atomic, Molecular & Chemical; Spectroscopy Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/68698