An imaging photoelectron photoion coincidence spectrometer at the vacuum ultraviolet (VUV) beamline of Swiss Light Source is presented and a few initial measurements are reported. Monochromatic synchrotron VUV radiation ionizes cooled or thermal gas-phase sample. Photoelectrons velocity focused, with better than 1 meV resolution for threshold electrons, also act as start signal ion time-of-flight analysis. The ions accelerated in relatively low, 40-80 V cm(-1) field, which enables direct...

Three data acquisition schemes for two-particle coincidence experiments with a continuous source are discussed. The single-start/single-stop technique, implemented time-to-pulse-height converter, results in complicated spectrum and breaks down severely at high count rates. single-start/multiple-stop setup, based on time-to-digital converter the first choice today’s similar experiments, performs significantly better rates, but its performance is still hampered if time-of-flight range large,...

Abstract A computer program has been developed to model and analyze the data from photoelectron photoion coincidence (PEPICO) spectroscopy experiments. This code used during past 12 years extract thermochemical kinetics information for almost a hundred systems, results have published in over forty papers. It models dissociative photoionization process threshold PEPICO experiment by calculating thermal energy distribution of neutral molecule, molecular ion as function photon energy,...

The vacuum ultraviolet (VUV) beamline of the Swiss Light Source has been upgraded after two years operation. A new, turntable-type monochromator was constructed at Paul Scherrer Institut, which allows for fast yaw-alignment as well quick grating change and exchange. In addition to original imaging photoelectron photoion coincidence endstation (iPEPICO), a second, complementary double setup (i2PEPICO) built. Volatile samples can be introduced room temperature or in molecular beam, pyrolysis...

Determining the structure of active Cu sites, which are associated with methane conversion intermediate during stepwise, low-temperature, methane-to-methanol conversion, represents an important step for upgrade this reaction route to a viable process. Quick X-ray absorption spectroscopy allowed us follow electronic and structural changes sites desorption activated intermediate. A large fraction (41%) oxygen-activated CuII reacted underwent reduction CuI. When was released as product MeOH...

Abstract Catalytic fast pyrolysis is a promising way to convert lignin into fine chemicals and fuels, but current approaches lack selectivity yield unsatisfactory conversion. Understanding the reaction mechanism at molecular level may help make this sustainable process more economic. Reactive intermediates are responsible for product branching hold key unveiling these mechanisms, notoriously difficult detect isomer-selectively. Here, we investigate catalytic of guaiacol, model compound,...

Photoelectron photoion coincidence (PEPICO) spectroscopy could become a powerful tool for the time-resolved study of multi-channel gas phase chemical reactions. Toward this goal, we have designed and tested electron ion optics that form core new PEPICO spectrometer, utilizing simultaneous velocity map imaging both cations electrons, while also achieving good cation mass resolution through space focusing. These are combined with side-sampled, slow-flow reactor photolytic initiation gas-phase...

Dicopper species have been identified as the active sites in converting methane to methanol Cu-zeolites. To understand formation of these copper cores mordenite, we used situ time-resolved X-ray absorption spectroscopy during heat treatment. Significant dehydration enabled reduction cores, after which molecular oxygen was cleaved. The activated bridged two atoms make reactive precursor for activation methane. Even though bridging detected, XAS data were unable distinguish a...

The production of phosphoryl species (PO, PO2, HOPO) is believed to be great importance for efficient flame-retardant action in the gas phase. We present a detailed investigation thermal decomposition dimethyl methylphosphonate (DMMP) probed by vacuum ultraviolet (VUV) synchrotron radiation and imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. This technique provides snapshot thermolysis process direct evidence how reactive are generated during heat exposure. One key...

Adaptation of a low-pressure flat flame burner with flame-sampling interface to the imaging photoelectron photoion coincidence spectrometer (iPEPICO) VUV beamline at Swiss Light Source is presented. The combination molecular-beam mass spectrometry and iPEPICO provides new powerful analytical tool for detailed investigation reaction networks in flames. First results demonstrate applicability instrument comprehensive diagnostics potentially high impact mechanism development conventional...

How can we detect reactive and elusive intermediates in catalysis to unveil reaction mechanisms? In this mini review, discuss novel photoionization tools support quest.

Clean combustion, i.e., the reduction of NOx and soot emissions, carbon neutrality, achieved in part by biofuel synthesis, are major milestones transition to a sustainable future. To overcome empiric time-consuming process optimization steps, we need detailed reaction mechanistic chemical insights on these processes. Be it combustion or catalysis, highly reactive intermediates, such as radicals, carbenes, ketenes drive reactions. Knowing fate species helps develop strategies optimize energy...

Abstract Understanding hydrocarbon generation in the zeolite-catalysed conversions of methanol and methyl chloride requires advanced spectroscopic approaches to distinguish complex mechanisms governing C–C bond formation, chain growth deposition carbonaceous species. Here operando photoelectron photoion coincidence (PEPICO) spectroscopy enables isomer-selective identification pathways hydrocarbons up C 14 size, providing direct experimental evidence radicals both reactions ketene...

The catalytic pyrolysis mechanism of the initial lignin depolymerization products will help us develop biomass valorization strategies. How does isomerism influence reactivity, product formation, selectivities, and side reactions? By using imaging photoelectron photoion coincidence (iPEPICO) spectroscopy with synchrotron radiation, we reveal initial, short-lived reactive intermediates driving benzenediol over H-ZSM-5 catalyst. detailed reaction unveils new pathways leading to most important...

Oxidative dehydrogenation of propane (ODHP) is an emerging technology to meet the global propylene demand with boron nitride (BN) catalysts likely play a pivotal role. It widely accepted that gas-phase chemistry plays fundamental role in BN-catalyzed ODHP. However, mechanism remains elusive because short-lived intermediates are difficult capture. We detect free radicals (CH3•, C3H5•) and reactive oxygenates, C2-4 ketenes C2-3 enols, ODHP over BN by operando synchrotron photoelectron photoion...

Photoionization mass spectrometry is a powerful method for time- and space-resolved chemical analysis of reactants, intermediates, products. Tunable synchrotron light enables isomer separation based on unique photoionization spectra; however, mixtures three or more isomers can be difficult to resolve by this method. In work we demonstrate, measuring the photoelectron spectrum corresponding each cation m/z ratio, that imaging photoion coincidence spectroscopy provides detailed spectral...

The dissociation of the naphthalene radical cation has been reinvestigated here by a combination tandem mass spectrometry and imaging photoelectron photoion coincidence spectroscopy (iPEPICO). Six reactions were explored: (R1) C(10)H(8)(•+) → C(10)H(7)(+) + H (m/z = 127); (R2) C(8)H(6)(•+) C(2)H(2) 102); (R3) C(6)H(6)(•+) C(4)H(2) 78); (R4) C(10)H(6)(•+) H(2) 126); (R5) C(6)H(5)(+) 77); (R6) 126). E(0) activation energies for deduced from present measurements are (in eV) 4.20 ± 0.04 (R1),...

The unimolecular dissociation of the pyrene radical cation, C16H10(+•), has been explored using a combination computational techniques and experimental approaches, such as multiple photon absorption in cold ion trap Piège à Ions pour la Recherche et l'Etude de Nouvelles Espèces Astrochimiques (PIRENEA) imaging photoelectron photoion coincidence spectrometry (iPEPICO). In total, 22 reactions, involving fragmentation cascade (H, C2H2, C4H2 loss) from cation down to C14(+•) fragment ion, have...

Imaging photoelectron photoion coincidence spectroscopy was employed to explore the unimolecular dissociation of ionized polycyclic aromatic hydrocarbons (PAHs) acenaphthylene, fluorene, cyclopenta[d,e,f]phenanthrene, pyrene, perylene, fluoranthene, dibenzo[a,e]pyrene, dibenzo[a,l]pyrene, coronene and corannulene. The primary reaction is always hydrogen atom loss, with smaller species also exhibiting loss C2H2 varying extents. Combined previous work on PAH ions, trends in energies (E0) for H...

Resistively heated silicon carbide microreactors are widely applied as continuous sources to selectively prepare elusive and reactive intermediates with astrochemical, catalytic, or combustion relevance measure their photoelectron spectrum. These reactors also provide deep mechanistic insights into uni- bimolecular chemistry. However, the sampling conditions effects have not been fully characterized. We use cation velocity map imaging distribution of molecular beam signal quantify scattered,...

Unveiling catalytic mechanisms at a molecular level aids rational catalyst design and selectivity control for process optimization. In this study, we find that the Brønsted acid site density of zeolite efficiently controls guaiacol pyrolysis mechanism. Guaiacol demethylation to catechol initiates reaction, as evidenced by detected methyl radicals. The mechanism branches form either fulvenone (c-C5H4 = C O), reactive ketene intermediate, dehydration, or phenol acid-catalyzed dehydroxylation....

The dissociative photoionization studies have been performed for a set of dihalomethane CH2XY (X,Y = Cl, Br, and I) molecules employing the threshold photoelectron photoion coincidence (TPEPICO) technique. Accurate dissociation onsets first second limits recorded in 10−13 eV energy range, ionization potentials measured these compounds. By using our experimental known heat formation CH2Cl2 molecule, it has possible to derive 0 298 K heats all six neutral dihalomethanes as well their ionic...