Mass-Resolved Isomer-Selective Chemical Analysis with Imaging Photoelectron Photoion Coincidence Spectroscopy

Abstract

Photoionization mass spectrometry is a powerful method for time-and space-resolved chemical analysis of reactants, intermediates, and products. Tunable synchrotron light enables isomer separation based on unique photoionization spectra; however, mixtures of three or more isomers can be difficult to resolve by this method. In this work we demonstrate, by measuring the photoelectron spectrum corresponding to each cation m/z ratio, that imaging photoelectron photoion coincidence spectroscopy provides a more detailed spectral fingerprint than photoionization spectra. This method offers increased selectivity for analyzing gas-phase mixtures of many components. Mixtures of two C 4 H 6 and four C 5 H 8 unsaturated hydrocarbons were analyzed, and the components could easily be identified based on mass-selected threshold photoelectron spectra (scanning the photon energy) or photoelectron velocity map images (PEVMIs) at a single or a few fixed photon energies. The PEVMI approach is more highly multiplexed, trading somewhat lower spectral resolution for faster data acquisition and photoelectron angular distributions.

Determination of accurate electron chiral asymmetries in fenchone and camphor in the VUV range: sensitivity to isomerism and enantiomeric purity

“…This ability of PECD could be applied in the future in the field of gas phase chemical reactivity, in order to probe and disentangle isomers in chemical reactions involving chiral products, as for instance in combustion of biofuels. PECD, with its exquisite sensitivity to isomers would be, in this context of gas phase chemical reactions probed by photoionization, an additional observable to products appearance energies 64 , or even to the full PES of mass--selected species 65,66 . …”

Insights into gas-phase reaction mechanisms of small carbon radicals using isomer-resolved product detection

“…46 The article by Bodi et al discusses the virtues of the iPEPICO method for isomer-specific detection of gas-phase mixtures. 45 Laboratory-based tabletop techniques continue to develop for the isomer-specific product detection of gas-phase species. Near-infrared femtosecond laser pulse can be used to selectively ionize isomers through strong field ionization.…”

Dissociative Photoionization of Diethyl Ether

“…4) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 For technical reasons, the sequential dissociation product abundances from methyl loss, i.e. m/z = 31 [13], and 29 [14], were added to their parent ion, C 3 .81 ± 0.05 eV, respectively. As can be seen in Fig.…”

“…Another experimental result ibid., derived from the dissociative ionization of CH 3 CH 2 OCH 2 CH 2 OH, 638 kJ mol −1 , is in agreement with the 0 K value determined in this work. To support the revised heat of formation, the thermochemical onset of CH 3 namely CH 2 OH + [13] and C 2 H 5 + [14], the 0 K heats of formation can be derived as 711 ± 7…”

“…O +[13] signal and the coincident drop in the C 3 H 7 O + [8] abundance indicates a consecutive channel from the methyl-loss product leading to CH 2 =OH +[13] by C 2 H 4 -loss at a phenomenological appearance energy of about 11.8 eV.At approximately the same energy, C 3 H 5 + (m/z = 41) also appears as a minor channel with a maximum intensity of less than 2%. This minor product ion can be formed by a complex H 2 O-loss step with a consecutive dissociation from the CH 3 −CH 2 −O=CH 2 + (m/z = 59) ion [8], and has not been included in the statistical model.…”