Rostock 2019 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 7: Experimental Techniques

MO 7.5: Vortrag

Montag, 11. März 2019, 15:00–15:15, S HS 002 Biologie

Distinction of ortho-, meta- and para-benzene derivatives by means of chirped femtosecond laser ionization — •Viola Schäfer and Karl-Michael Weitzel — Philipps-Universität Marburg, Fachbereich Chemie, Germany

The distinction of structural isomers, in particular ortho-, meta-, para-isomers of benzene derivatives poses a considerable challenge in situations, where chromatographic separation is not the method of choice. Distinction by means of electron impact mass spectrometry is in general not possible. Here, the combination of femtosecond laser ionization with time-of-flight mass spectrometry (fs-LIMS) constitutes an alternative, multi-dimensional technique with high analytical power. The variation of laser pulse parameters, e.g. the spectral phase, allows the distinction of structural isomers.[1] In the current work we present a systematic chirped fs-LIMS investigation of ortho-, meta- and para-isomers of fluorotoluene and fluorobenzyl bromide. The mass spectra for the isomers of the respective compound look similar for transform limited laser pulses. By variation of linear and quadratic chirp we are able to enhance small differences between the isomers for specific fragmentation channels. We demonstrate, that we are able to distinguish the structural isomers of both compounds. In this context we will address the mechanism for the formation of common intermediates and the dynamics involved. The influence of the substituents and their positions at the benzene ring, as well as the relevance of specific fragments, e.g. tropylium and benzylium ions, will be discussed. [1] N. Reusch, V. Krein, N. Wollscheid, K.-M. Weitzel, Z.f.Phys.Chem., 232, 689, (2018)