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Issue 2, 2014
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Imaging breakdown diagrams for bromobutyne isomers with photoelectron–photoion coincidence

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Abstract

Internal energy selected C4H5Br+ ions were prepared by vacuum ultraviolet photoionization from the bromobutyne constitutional isomers 4-bromo-1-butyne, 1-bromo-2-butyne, and 3-bromo-1-butyne. The lowest energy dissociative photoionization channel is Br-loss. 1-Bromo-2-butyne and 3-bromo-1-butyne cations are not metastable, and based on the threshold photoionization breakdown diagrams and neutral internal energy distributions, 0 K appearance energies of E0 = 10.375 ± 0.010 and 10.284 ± 0.010 eV are obtained, respectively. A kinetic shift has been observed in the Br loss of the 4-bromo-1-butyne cation, and the experimental dissociation rates were also modeled to obtain E0 = 10.616 ± 0.030 eV. The energetics of the samples and nine C4H5 and C4H5+ structures are explored using G4 theory, which suggests that only the staggered 4-bromo-1-butyne rotamer cation loses Br to form a high-energy cyclic C4H5+ isomer, while the relative appearance energies indicate that 1-bromo-2-butyne and 3-bromo-1-butyne form the linear CH2CCCH3+ ion. The subtraction scheme for hot electron suppression in threshold photoelectron–photoion coincidence (TPEPICO) is discussed, and is used to introduce velocity map imaging (VMI-)PEPICO and data analysis. The derived onsets and the dissociation rate curve show that modeling VMI-PEPICO data taken close above or below the disappearance energy of the parent ion to obtain imaging breakdown diagrams is a feasible approach also in the presence of a kinetic shift. Imaging breakdown diagrams are advantageous when signal levels are low or short acquisition times necessary, such as in the case of reactive intermediates or in time resolved experiments, and can also be used as a fast molecular thermometer.

Graphical abstract: Imaging breakdown diagrams for bromobutyne isomers with photoelectron–photoion coincidence

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Publication details

The article was received on 30 Jul 2013, accepted on 19 Sep 2013 and first published on 19 Sep 2013


Article type: Paper
DOI: 10.1039/C3CP53212G
Phys. Chem. Chem. Phys., 2014,16, 505-515
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    Imaging breakdown diagrams for bromobutyne isomers with photoelectron–photoion coincidence

    A. Bodi and P. Hemberger, Phys. Chem. Chem. Phys., 2014, 16, 505
    DOI: 10.1039/C3CP53212G

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