Iodine atom loss kinetics in internal energy selected 1-iodoalkane cations by imaging photoelectron photoion coincidence spectroscopy

Rowland, Tyson G.; Borkar, Sampada; Bodi, Andras; Sztáray, Bálint

doi:10.1016/j.ijms.2014.07.028

Cited by 8 publications

(40 citation statements)

References 65 publications

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“…Modeling breakdown curves often yields insight into the dissociative ionization mechanism (e.g., Hemberger et al 2013) or can provide highly accurate thermochemical values such as bond dissociation energies and heats of formation (e.g., Bodi et al 2014;Rowland et al 2015;Voronova et al 2018). An analysis of the breakdown graph according to the RRKM model has been performed with Sztáray et al (2010)'s program minipepico (version 194i).…”

Section: Rrkm Analysismentioning

confidence: 99%

Threshold Dissociation of the 1-ethynylpyrene Cation at Internal Energies Relevant to H i Regions

Rouillé

Steglich

Hemberger

et al. 2019

ApJ

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Photoelectron photoion coincidence spectroscopy has been used to measure the threshold photoelectron spectrum of 1-ethynylpyrene and to obtain the breakdown graph describing the dissociation of the 1-ethynylpyrene cation. The threshold photoelectron measurement has allowed us to improve the determination of the ionization energy of 1-ethynylpyrene at 7.391 ± 0.005 eV. Concerning the main dissociation channels, the analysis of the breakdown graph has given 3.70 ± 0.60 eV as the activation energy for the loss of one H atom and 2.98 ± 1.80 eV for the loss of a second independent H atom. The corresponding entropies of activation are affected by large errors as observed in similar studies of other polycyclic aromatic hydrocarbon cations. Minor dissociation channels were also detected and identified as the loss of the C 2 H group and the loss of a C 2 H 2 unit and/or that of an H atom plus the C 2 H group. The activation energies and the entropies of activation of these minor pathways could not be derived from the measurements. It is found that the cation of 1-ethynylpyrene behaves like the cation of pyrene and is consequently more photostable than the cation of 1-methylpyrene. We conclude that photodissociation is not the leading cause of the low abundance, if not the absence, of ethynyl-substituted polycyclic aromatic hydrocarbon species in the interstellar medium.

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Section: Rrkm Analysismentioning

confidence: 99%

Threshold Dissociation of the 1-ethynylpyrene Cation at Internal Energies Relevant to H i Regions

Rouillé

Steglich

Hemberger

et al. 2019

ApJ

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“…Both energetic arguments and the slope of the breakdown curves suggest that the m/z 55 [18] and 41 [20] fragment ions are formed in consecutive dissociation steps of the X-loss fragment ion at m/z 83 [11] from X = Br and I. In the reaction pathways shown in Figure 4, the energy is referenced to the cyclohexyl cation [11].…”

Section: Resultsmentioning

confidence: 99%

Dissociative Photoionization of Chloro-, Bromo-, and Iodocyclohexane: Thermochemistry and the Weak C–Br Bond in the Cation

Zhou

Hemberger

et al. 2021

J. Phys. Chem. A

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Double-imaging photoelectron photoion coincidence spectroscopy (i 2PEPICO) with tunable synchrotron vacuum ultraviolet radiation was used to record threshold ionization mass spectra of the halocyclohexanes C6H11X (X = Cl, Br, and I). Calculations show that experimental dissociative ionization thresholds correspond to thermochemical limits. Among the processes observed (X loss, followed by C2H4 or C3H6 loss; C2H3Cl loss; HCl loss, followed by CH3 or C2H4 loss), halogen atom loss can be used to derive enthalpies of formation and C–X bond energies in the cation. As an ancillary value, we propose a new proton affinity for cyclohexene at PA298K(c-C6H10) = 771.5 ± 1.7 kJ mol–1. The halogen loss onsets 10.74 ± 0.06 eV, 10.125 ± 0.005, and 9.474 ± 0.005 eV thus yield Δf H o 298K(C6H11X (g)) = −164.4 ± 6.2, −114.4 ± 2.3, and −56.3 ± 2.3 kJ mol–1 for X = Cl, Br, and I, respectively. The last two agree with DFT-calculated isodesmic reaction energies very well, as opposed to G4 theory for X = Br. The C–X bond energy in the cation is the lowest for X = Br. This is the sum result of the weakening C–X bond in the neutral and the increasing stabilization of the parent ion with increasing halogen size.

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“…Furthermore, the appearance energy connects the enthalpies of formation of the neutral and the fragments in such cases and can often be used in thermochemical cycles to derive new energetics data, such as enthalpies of formation , or proton affinities . If there is a transition state at an energy higher than that of the products, the appearance energy can be used to determine the heat of formation of the activated complex accurately, which can be used, e.g., to benchmark computational approaches …”

Section: Computational Sectionmentioning

confidence: 99%

“…54 If there is a transition state at an energy higher than that of the products, the appearance energy can be used to determine the heat of formation of the activated complex accurately, which can be used, e.g., to benchmark computational approaches. 55 The Journal of Physical Chemistry A 1. Threshold Photoelectron Spectrum.…”

Section: Computational Sectionmentioning

confidence: 99%

Photoionization of Two Potential Biofuel Additives: γ-Valerolactone and Methyl Butyrate

et al. 2021

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The photoionization of two potential biofuel additives, γ-valerolactone (GVL, C 5 H 8 O 2 ) and methyl butyrate (MB, C 5 H 10 O 2 ) has been studied by imaging photoelectron photoion coincidence spectroscopy (iPEPICO) at the VUV beamline of the Swiss Light Source (SLS). The vibrational fine structure in the photoelectron spectrum is compared with a Franck−Condon simulation for the electronic ground-state band of the GVL cation. In the lowest energy dissociative photoionization channel of GVL, CO 2 is lost, resulting in a 1-butene fragment ion with a 0 K appearance energy of E 0 = 10.35 ± 0.01 eV. A newly calculated 1-butene ionization energy of 9.595 ± 0.015 eV establishes the reverse barrier height to CO 2 loss as 66.6 ± 4.3 kJ mol −1 . Methyl butyrate cations undergo McLafferty rearrangement, which explains the missing ion signal at the computed adiabatic ionization energy of 9.25 eV. After H transfer, ethylene is lost in the lowest energy dissociation channel to yield the methyl acetate enol ion at E 0 = 10.24 ± 0.04 eV. This value connects the energetics of methyl butyrate with that of methyl acetate enol ion, which is established atParallel to ethylene loss, methyl loss is also observed from the enol tautomer of the parent ion. Both samples exhibit low-energy nonstatistical dissociative ionization channels. In GVL, the methyl-loss abundance rises quickly but levels off suddenly in the energy range of the first electronically excited states, indicating nonstatistical competition between CH 3 and CO 2 loss. In MB, the major parallel dissociation channel is the loss of a methoxy radical. Calculations indicate that McLafferty rearrangement is inhibited on the excited-state surface. Indeed, breakdown curve modeling of this and a sequential CO-loss channel confirms a second statistical regime in dissociative photoionization, decoupled from ethylene loss.

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Iodine atom loss kinetics in internal energy selected 1-iodoalkane cations by imaging photoelectron photoion coincidence spectroscopy

Cited by 8 publications

References 65 publications

Threshold Dissociation of the 1-ethynylpyrene Cation at Internal Energies Relevant to H i Regions

Threshold Dissociation of the 1-ethynylpyrene Cation at Internal Energies Relevant to H i Regions

Dissociative Photoionization of Chloro-, Bromo-, and Iodocyclohexane: Thermochemistry and the Weak C–Br Bond in the Cation

Photoionization of Two Potential Biofuel Additives: γ-Valerolactone and Methyl Butyrate

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