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MO: Fachverband Molekülphysik

MO 16: Electronic Spectroscopy II

MO 16.1: Hauptvortrag

Mittwoch, 10. März 2010, 16:30–17:00, F 102

Probing molecular chirality in a laser mass spectrometer: Circular dichroism and multiphoton ionization — •Ulrich Boesl and Christoph Logé — TUM Chemie Department, Physikalische Chemie, 85747 Garching

The chirality of molecules is usually probed by chiral chromatography (CC) or circular dichroism (CD). CD is the small difference in absorption of left and right-handed circularly polarized light by chiral molecules. CC is due to different behaviour of homo- and hetero-diasteriomeric complexes formed between chiral sample molecules and the chiral stationary chromatographic phase. The behaviour of diasteriomeric complexes has also been exploited to probe molecular chirality with mass spectrometric means. These are based on difference in chemical stability (different fragment-ion pattern) or in UV-spectroscopy (different ion current at resonance-enhanced multiphoton ionization - REMPI) of homo- and hetero-complexes Our approach to probe molecular chirality in a mass spectrometer is the combination of circular dichroism and REMPI (1). We succeeded in measuring CD-laser mass spectra as well as mass selected CD-laser spectra of 3-Methyl-Cyclopentanone. We found several effects, such as cumulating CD in double-resonant REMPI and CD of two-photon absorption which differs strongly from CD of one-photon transitions. Reference substances and a double laser beam setup have been applied to increase the resolution for small absorption differences and thus of small CD-effects. (1) U. Boesl, A. Bornschlegl, ChemPhysChem 7 (2006) 2085. Ch. Logé, A. Bornschlegl, U. Boesl, Anal. Bioanal. Chem. 395 (2009) 1631