Threshold ionization spectroscopic investigation of supersonic jet-cooled, laser-desorbed Tryptophan

Taherkhani, Mehran; Armentano, Antonio; Černý, Jiří; Müller‐Dethlefs, Klaus

doi:10.1016/j.cplett.2016.05.061

Cited by 1 publication

(1 citation statement)

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“…Several dedicated sample delivery systems have been designed to bring non‐volatile compounds into the gas phase to study their molecular properties. Aside from (matrix‐assisted) laser desorption, samples can be evaporated in a heated oven in a buffer gas, and expanded into vacuum to create a cold molecular beam of the isolated species as well as clusters thereof, and to study the unimolecular decomposition mechanism of the sample by pyrolysis . Such a molecular beam source requires that the vapor pressure of the sample is on the order of 1 mbar before thermal decomposition sets in.…”

Section: Experimental and Computational Methodsmentioning

confidence: 99%

The Distant Double Bond Determines the Fate of the Carboxylic Group in the Dissociative Photoionization of Oleic Acid

et al. 2017

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The valence threshold photoionization of oleic acid has been studied using synchrotron VUV radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. An oleic acid aerosol beam was impacted on a copper thermodesorber, heated to 130 °C, to evaporate the particles quantitatively. Upon threshold photoionization, oleic acid produces the intact parent ion first, followed by dehydration at higher energies. Starting at ca. 10 eV, a large number of fragment ions slowly rise suggesting several fragmentation coordinates with quasi-degenerate activation energies. However, water loss is the dominant low-energy dissociation channel, and it is shown to be closely related to the unsaturated carbon chain. In the lowest-barrier process, one of the four allylic hydrogen atoms is transferred to the carboxyl group to form the leaving water molecule and a cyclic ketone fragment ion. A statistical model to analyze the breakdown diagram and measured rate constants yields a 0 K appearance energy of 9.77 eV, which can be compared with the density functional theory result of 9.19 eV. Alternative H-transfer steps yielding a terminal C=O group are ruled out based on energetics and kinetics arguments. Some of the previous photoionization mass spectrometric studies also reported 2 amu and 26 amu loss fragment ions, corresponding to hydrogen and acetylene loss. We could not identify such peaks in the mass spectrum of oleic acid.

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Section: Experimental and Computational Methodsmentioning

confidence: 99%