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Balint Sztaray - One of the best experts on this subject based on the ideXlab platform.
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Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet (VUV) photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence (i2PEPICO). A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum(SPES) of CH3O2 was obtained exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A′′ and a1A′overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy (AIE) of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracytheoretical data from the literature. The vertical ionization Energy of the b1A' electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.1548 ± 0.020 eV.
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vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence. A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum (SPES) of CH3O2 was obtained, exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A″ and a1A′ overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracy theoretical data from the literature. The vertical ionization Energy of the b1A′ electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2 fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.15 ± 0.02 eV.
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dissociative photoionization of chromium hexacarbonyl a round trip ticket to non statisticality and a detective story in thermochemistry
International Journal of Mass Spectrometry, 2019Co-Authors: Krisztina Voronova, Krisztián G. Torma, Andras Bodi, James P Kercher, Balint SztarayAbstract:Abstract The fragmentation processes of internal Energy selected chromium hexacarbonyl cations, Cr(CO)6+, were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy at the VUV beamline of the Swiss Light Source. In the 9.3–21.5 eV photon Energy range, Cr(CO)6+ dissociates by six sequential carbonyl ligand losses. The fragment ion fractional abundances, plotted in the breakdown diagram, along with the time-of-flight mass spectra for the first three metastable CO-loss channels were modeled using a statistical approach. Between 12 and 16 eV, the statistical model overestimates the degree of fragmentation, which is explained by enhanced kinetic Energy release in impulsive CO loss on repulsive electronic states of the parent ion Cr(CO)6+, as confirmed by TD-DFT calculations. This is the first reported example for an embedded non-statistical unimolecular dissociation regime, bracketed by statistical regimes at low and at high energies. The statistical model was employed to derive 0 K Appearance energies for Cr(CO)n+ (n = 0–5). The Cr(CO)5+ Appearance Energy and the literature CO Cr(CO)5+ bond dissociation Energy yield an adiabatic Cr(CO)6+ ionization Energy of 8.195 ± 0.120 eV, independent of photoelectron spectroscopy measurements. The 0 K Appearance Energy of Cr+ is 61 kJ mol–1 higher than predicted based on literature enthalpies of formation, which we suggest is most likely due to an error in the enthalpy of formation of Cr(CO)6, and propose a revised ΔfH[Cr(CO)6, g] = –972.1 ± 4.1 and –968.9 ± 4.1 kJ mol–1 at 0 and 298 K, respectively, and ΔfH298K[Cr(CO)6, c] = –1040.6 ± 4.2 kJ mol–1 for the crystalline state, based on the known enthalpy of sublimation. The measured Cr CO bond dissociation energies in [(CO)nCr CO]+ (n = 0–5), and the enthalpies of formation of the chromium carbonyl ion series are also reported.
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dissociative photoionization of the c7h8 isomers cycloheptatriene and toluene looking at two sides of the same coin simultaneously
Journal of Physical Chemistry A, 2019Co-Authors: Krisztian G Torma, Krisztina Voronova, Balint Sztaray, Andras BodiAbstract:The dissociation of Energy-selected 1,3,5-cycloheptatriene (CHT) and toluene (Tol) cations was investigated by imaging photoelectron photoion coincidence spectroscopy. In the measured Energy ranges of 10.30-11.75 eV for CHT and 11.45-12.55 eV for Tol, only the hydrogen atom loss channels open up, leading to C7H7+ from both molecular ions, which are both metastable at the H-loss threshold. Quantum chemical calculations showed that an interconversion of the molecular ions happens below the dissociation threshold. Therefore, a single statistical model was constructed to describe both systems simultaneously. We determined 0 K Appearance energies for the tropylium (Tr+) and benzyl (Bz+) fragment ions from CHT to be 9.520 ± 0.060 and 9.738 ± 0.082 eV and that from Tol to be 10.978 ± 0.063 and 11.196 ± 0.080 eV, respectively. Using the experimentally determined benzyl ion Appearance Energy, its 0 K heat of formation was calculated to be 937.9 ± 7.7 kJ mol-1. Finally, on the basis of this value and the recently determined benzyl ionization Energy, we point out discrepancies concerning the benzyl radical thermochemistry.
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Radical Thermometers, Thermochemistry, and Photoelectron Spectra: A Photoelectron Photoion Coincidence Spectroscopy Study of the Methyl Peroxy Radical.
Journal of Physical Chemistry Letters, 2018Co-Authors: Krisztina Voronova, Patrick Hemberger, Thomas Gerber, David L. Osborn, Krisztián G. Torma, Kent M. Ervin, Andras Bodi, Balint SztarayAbstract:We investigated the simplest alkylperoxy radical, CH3OO, formed by reacting photolytically generated CH3 radicals with O2, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck–Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization Energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH3OO generates the CH3+ fragment ion at the Appearance Energy of 11.164 ± 0.010 eV. Combining these two values with ΔfH0K°(CH3) yields ΔfH0K°(CH3OO) = 22.06 ± 0.97 kJ mol–1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH3OO breakdown diagram provides a molecular thermometer of the free radical’s internal temperature, which we measured to be 330 ± 30 K.
Branko Ruscic - One of the best experts on this subject based on the ideXlab platform.
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a vacuum ultraviolet laser pulsed field ionization photoion study of methane ch4 determination of the Appearance Energy of methylium from methane with unprecedented precision and the resulting impact on the bond dissociation energies of ch4 and ch4
Physical Chemistry Chemical Physics, 2017Co-Authors: Yih Chung Chang, Branko Ruscic, Bo Xiong, David H BrossAbstract:We report on the successful implementation of a high-resolution vacuum ultraviolet (VUV) laser pulsed field ionization-photoion (PFI-PI) detection method for the study of unimolecular dissociation of quantum-state- or Energy-selected molecular ions. As a test case, we have determined the 0 K Appearance Energy (AE0) for the formation of methylium, CH3+, from methane, CH4, as AE0(CH3+/CH4) = 14.32271 ± 0.00013 eV. This value has a significantly smaller error limit, but is otherwise consistent with previous laboratory and/or synchrotron-based studies of this dissociative photoionization onset. Furthermore, the sum of the VUV laser PFI-PI spectra obtained for the parent CH4+ ion and the fragment CH3+ ions of methane is found to agree with the earlier VUV pulsed field ionization-photoelectron (VUV-PFI-PE) spectrum of methane, providing unambiguous validation of the previous interpretation that the sharp VUV-PFI-PE step observed at the AE0(CH3+/CH4) threshold ensues because of higher PFI detection efficiency for fragment CH3+ than for parent CH4+. This, in turn, is a consequence of the underlying high-n Rydberg dissociation mechanism for the dissociative photoionization of CH4, which was proposed in previous synchrotron-based VUV-PFI-PE and VUV-PFI-PEPICO studies of CH4. The present highly accurate 0 K dissociative ionization threshold for CH4 can be utilized to derive accurate values for the bond dissociation energies of methane and methane cation. For methane, the straightforward application of sequential thermochemistry via the positive ion cycle leads to some ambiguity because of two competing VUV-PFI-PE literature values for the ionization Energy of methyl radical. The ambiguity is successfully resolved by applying the Active Thermochemical Tables (ATcT) approach, resulting in D0(H–CH3) = 432.463 ± 0.027 kJ mol−1 and D0(H–CH3+) = 164.701 ± 0.038 kJ mol−1.
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on the enthalpy of formation of hydroxyl radical and gas phase bond dissociation energies of water and hydroxyl
Journal of Physical Chemistry A, 2002Co-Authors: Branko Ruscic, David Feller, David A Dixon, Kirk A Peterson, Lawrence B Harding, Albert F Wagner, Ximei Qian, R L Asher, Yang Song, Jianbo LiuAbstract:In a recent letter (J. Phys. Chem. A, 2001, 105,1), we argued that, although all major thermochemical tables recommend a value of (OH) based on a spectroscopic approach, the correct value is 0.5 kcal/mol lower as determined from an ion cycle. In this paper, we expand upon and augment both the experimental and theoretical arguments presented in the letter. In particular, three separate experiments (mass-selected photoionization measurements, pulsed-field-ionization photoelectron spectroscopy measurements, and photoelectron-photoion coincidence measurements) utilizing the positive ion cycle to derive the O−H bond Energy are shown to converge to a consensus value of the Appearance Energy AE0(OH+/H2O) = 146117 ± 24 cm-1 (18.1162 ± 0.0030 eV). With the most accurate currently available zero kinetic Energy photoionization value for the ionization Energy IE(OH) = 104989 ± 2 cm-1, corroborated by a number of photoelectron measurements, this leads to D0(H−OH) = 41128 ± 24 cm-1 = 117.59 ± 0.07 kcal/mol. This corres...
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evidence for a lower enthalpy of formation of hydroxyl radical and a lower gas phase bond dissociation Energy of water
Journal of Physical Chemistry A, 2001Co-Authors: Branko Ruscic, David Feller, David A Dixon, Kirk A Peterson, Lawrence B Harding, And Robert L Asher, Albert F WagnerAbstract:There are two experimental approaches to determining ΔHf0°(OH), which produce values of this key thermodynamic quantity that differ by >0.5 kcal/mol. The apparent uncertainty of the positive ion cycle approach resides in the measurement of the Appearance Energy of OH+ from H2O, while the uncertainty of the spectroscopic approach resides in the determination of the dissociation Energy of OH(A2Σ+). In this note we present an independent experimental determination of the Appearance Energy that confirms the accuracy and enhances the precision of the existing positive ion cycle value for ΔHf0°(OH). We also present electronic structure calculations of the OH(A2Σ+) potential Energy curve, which suggest that the extrapolation method used to obtain the spectroscopic dissociation Energy is in error. Finally, we present the largest ab initio electronic structure calculations ever performed for ΔHf0°(OH) that have an apparent uncertainty much less than 0.5 kcal/mol and support only the positive ion cycle value. Altho...
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ionization Energy of methylene revisited improved values for the enthalpy of formation of ch2 and the bond dissociation Energy of ch3 via simultaneous solution of the local thermochemical network
Journal of Physical Chemistry A, 1999Co-Authors: Branko Ruscic, Maritoni Litorja, R L AsherAbstract:The Appearance Energy of the CH2+ fragment from CH2CO has been carefully remeasured and fitted by a model curve, producing EA0(CH2+/CH2CO) = 13.743 ± 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for EI(CH2), D0(H−CH2), ΔH°f 0(CH2), and ΔH°f 0(CH2CO). A set of values with a statistically larger weight is produced by analyzing a local thermochemical network, which combines the present measurement with thirteen other experimental determinations from the literature and encompasses the enthalpies of formation of CH3, CH3+, CH2, CH2+, and CH2CO. The recommended simultaneously adjusted thermochemical values are: ΔH°f 0(CH3) = 35.86 ± 0.07 kcal/mol (35.05 ± 0.07 kcal/mol at 298 K), ΔH°f 0(CH3+) = 262.73 ± 0.06 kcal/mol (261.83 ± 0.06 kcal/mol at 298 K), ΔH°f 0(CH2) = 93.18 ± 0.20 kcal/mol (93.31 ± 0.20 kcal/mol at 298 K), ΔH°f 0(CH2+) = 332.92 ± 0.19 kcal/mol (333.04 ± 0.19 kcal/mol at 298 K), ΔH°f 0(CH2CO) = −11.10 ± 0.21 kcal/mol (−11.85 ...
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ionization Energy of methylene revisited improved values for the enthalpy of formation of ch2 and the bond dissociation Energy of ch3 via simultaneous solution of the local thermochemical network
Journal of Physical Chemistry A, 1999Co-Authors: Branko Ruscic, Maritoni Litorja, R L AsherAbstract:The Appearance Energy of the CH{sub 2}{sup +} fragment from CH{sub 2}CO has been carefully remeasured and fitted by a model curve, producing EA{sub 0}(CH{sub 2}{sup +}/CH{sub 2}CO) = 13.743 {+-} 0.005 eV. This value can be sequentially propagated through selected thermochemical cycles to yield individual values for El(CH{sub 2}), D{sub 0}(H-CH{sub 2}), {Delta}H{sup o}{sub f 0}(CH{sub 2}CO). A set of values with a statistically larger weight is produced by analyzing a local thermochemical network, which combines the present measurement with thirteen other experimental determinations from the literature and encompasses the enthalpies of formation of CH{sub 3}, CH{sub 3}{sup +}, CH{sub 2}, CH{sub 2}{sup +}, and CH{sub 2}CO. The recommended simultaneously adjusted thermochemical values are: {Delta}H{sup o}{sub f 0}(CH{sub 3}) = 35.86 {+-} 0.07 kcal/mol (35.05 {+-} 0.07 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 3}{sup +}) = 262.73 {+-} 0.06 kcal/mol (261.83 {+-} 0.06 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}) = 93.18 {+-} 0.20 kcal/mol (93.31 {+-} 0.20 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}{sup +}) = 332.92 {+-} 0.19 kcal/mol (333.04 {+-} 0.19 kcal/mol at 298 K), {Delta}H{sup o}{sub f 0}(CH{sub 2}CO) = -11.10 {+-} 0.21 kcal/mol (-11.85 {+-} 0.21 kcal/mol atmore » 298 K), as well as D{sub 0}(H{sub 3}C-H) = 103.42 {+-} 0.03 kcal/mol (104.99 {+-} 0.03 kcal/mol at 298 K), D{sub 0}(H{sub 2}C-H) = 108.95 {+-} 0.20 kcal/mol (110.35 {+-} 0.20 kcal/mol at 298 K), D{sub 0}(H{sub 2}C{double_bond}CO) = 77.08 {+-} 0.02 kcal/mol (78.73 {+-} 0.02 kcal/mol at 298 K), El(CH{sub 3}) = 9.3830 {+-} 0.0005 eV, and El(CH{sub 2}) = 10.3962 {+-} 0.0036 eV. These values are in excellent agreement with current and several previous experimental measurements. The recommended enthalpy of formation of CH{sub 2} implies that the reaction of singlet methylene with water is essentially thermoneutral (to within {+-}0.2 kcal/mol) at 0 and 298 K, and slightly endothermic (0.5 {+-} 0.2 kcal/mol) at 1000 K.« less
Krisztina Voronova - One of the best experts on this subject based on the ideXlab platform.
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Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet (VUV) photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence (i2PEPICO). A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum(SPES) of CH3O2 was obtained exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A′′ and a1A′overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy (AIE) of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracytheoretical data from the literature. The vertical ionization Energy of the b1A' electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.1548 ± 0.020 eV.
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vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence. A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum (SPES) of CH3O2 was obtained, exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A″ and a1A′ overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracy theoretical data from the literature. The vertical ionization Energy of the b1A′ electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2 fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.15 ± 0.02 eV.
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dissociative photoionization of chromium hexacarbonyl a round trip ticket to non statisticality and a detective story in thermochemistry
International Journal of Mass Spectrometry, 2019Co-Authors: Krisztina Voronova, Krisztián G. Torma, Andras Bodi, James P Kercher, Balint SztarayAbstract:Abstract The fragmentation processes of internal Energy selected chromium hexacarbonyl cations, Cr(CO)6+, were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy at the VUV beamline of the Swiss Light Source. In the 9.3–21.5 eV photon Energy range, Cr(CO)6+ dissociates by six sequential carbonyl ligand losses. The fragment ion fractional abundances, plotted in the breakdown diagram, along with the time-of-flight mass spectra for the first three metastable CO-loss channels were modeled using a statistical approach. Between 12 and 16 eV, the statistical model overestimates the degree of fragmentation, which is explained by enhanced kinetic Energy release in impulsive CO loss on repulsive electronic states of the parent ion Cr(CO)6+, as confirmed by TD-DFT calculations. This is the first reported example for an embedded non-statistical unimolecular dissociation regime, bracketed by statistical regimes at low and at high energies. The statistical model was employed to derive 0 K Appearance energies for Cr(CO)n+ (n = 0–5). The Cr(CO)5+ Appearance Energy and the literature CO Cr(CO)5+ bond dissociation Energy yield an adiabatic Cr(CO)6+ ionization Energy of 8.195 ± 0.120 eV, independent of photoelectron spectroscopy measurements. The 0 K Appearance Energy of Cr+ is 61 kJ mol–1 higher than predicted based on literature enthalpies of formation, which we suggest is most likely due to an error in the enthalpy of formation of Cr(CO)6, and propose a revised ΔfH[Cr(CO)6, g] = –972.1 ± 4.1 and –968.9 ± 4.1 kJ mol–1 at 0 and 298 K, respectively, and ΔfH298K[Cr(CO)6, c] = –1040.6 ± 4.2 kJ mol–1 for the crystalline state, based on the known enthalpy of sublimation. The measured Cr CO bond dissociation energies in [(CO)nCr CO]+ (n = 0–5), and the enthalpies of formation of the chromium carbonyl ion series are also reported.
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dissociative photoionization of the c7h8 isomers cycloheptatriene and toluene looking at two sides of the same coin simultaneously
Journal of Physical Chemistry A, 2019Co-Authors: Krisztian G Torma, Krisztina Voronova, Balint Sztaray, Andras BodiAbstract:The dissociation of Energy-selected 1,3,5-cycloheptatriene (CHT) and toluene (Tol) cations was investigated by imaging photoelectron photoion coincidence spectroscopy. In the measured Energy ranges of 10.30-11.75 eV for CHT and 11.45-12.55 eV for Tol, only the hydrogen atom loss channels open up, leading to C7H7+ from both molecular ions, which are both metastable at the H-loss threshold. Quantum chemical calculations showed that an interconversion of the molecular ions happens below the dissociation threshold. Therefore, a single statistical model was constructed to describe both systems simultaneously. We determined 0 K Appearance energies for the tropylium (Tr+) and benzyl (Bz+) fragment ions from CHT to be 9.520 ± 0.060 and 9.738 ± 0.082 eV and that from Tol to be 10.978 ± 0.063 and 11.196 ± 0.080 eV, respectively. Using the experimentally determined benzyl ion Appearance Energy, its 0 K heat of formation was calculated to be 937.9 ± 7.7 kJ mol-1. Finally, on the basis of this value and the recently determined benzyl ionization Energy, we point out discrepancies concerning the benzyl radical thermochemistry.
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Radical Thermometers, Thermochemistry, and Photoelectron Spectra: A Photoelectron Photoion Coincidence Spectroscopy Study of the Methyl Peroxy Radical.
Journal of Physical Chemistry Letters, 2018Co-Authors: Krisztina Voronova, Patrick Hemberger, Thomas Gerber, David L. Osborn, Krisztián G. Torma, Kent M. Ervin, Andras Bodi, Balint SztarayAbstract:We investigated the simplest alkylperoxy radical, CH3OO, formed by reacting photolytically generated CH3 radicals with O2, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck–Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization Energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH3OO generates the CH3+ fragment ion at the Appearance Energy of 11.164 ± 0.010 eV. Combining these two values with ΔfH0K°(CH3) yields ΔfH0K°(CH3OO) = 22.06 ± 0.97 kJ mol–1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH3OO breakdown diagram provides a molecular thermometer of the free radical’s internal temperature, which we measured to be 330 ± 30 K.
Andras Bodi - One of the best experts on this subject based on the ideXlab platform.
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dissociative photoionization of chromium hexacarbonyl a round trip ticket to non statisticality and a detective story in thermochemistry
International Journal of Mass Spectrometry, 2019Co-Authors: Krisztina Voronova, Krisztián G. Torma, Andras Bodi, James P Kercher, Balint SztarayAbstract:Abstract The fragmentation processes of internal Energy selected chromium hexacarbonyl cations, Cr(CO)6+, were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy at the VUV beamline of the Swiss Light Source. In the 9.3–21.5 eV photon Energy range, Cr(CO)6+ dissociates by six sequential carbonyl ligand losses. The fragment ion fractional abundances, plotted in the breakdown diagram, along with the time-of-flight mass spectra for the first three metastable CO-loss channels were modeled using a statistical approach. Between 12 and 16 eV, the statistical model overestimates the degree of fragmentation, which is explained by enhanced kinetic Energy release in impulsive CO loss on repulsive electronic states of the parent ion Cr(CO)6+, as confirmed by TD-DFT calculations. This is the first reported example for an embedded non-statistical unimolecular dissociation regime, bracketed by statistical regimes at low and at high energies. The statistical model was employed to derive 0 K Appearance energies for Cr(CO)n+ (n = 0–5). The Cr(CO)5+ Appearance Energy and the literature CO Cr(CO)5+ bond dissociation Energy yield an adiabatic Cr(CO)6+ ionization Energy of 8.195 ± 0.120 eV, independent of photoelectron spectroscopy measurements. The 0 K Appearance Energy of Cr+ is 61 kJ mol–1 higher than predicted based on literature enthalpies of formation, which we suggest is most likely due to an error in the enthalpy of formation of Cr(CO)6, and propose a revised ΔfH[Cr(CO)6, g] = –972.1 ± 4.1 and –968.9 ± 4.1 kJ mol–1 at 0 and 298 K, respectively, and ΔfH298K[Cr(CO)6, c] = –1040.6 ± 4.2 kJ mol–1 for the crystalline state, based on the known enthalpy of sublimation. The measured Cr CO bond dissociation energies in [(CO)nCr CO]+ (n = 0–5), and the enthalpies of formation of the chromium carbonyl ion series are also reported.
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dissociative photoionization of the c7h8 isomers cycloheptatriene and toluene looking at two sides of the same coin simultaneously
Journal of Physical Chemistry A, 2019Co-Authors: Krisztian G Torma, Krisztina Voronova, Balint Sztaray, Andras BodiAbstract:The dissociation of Energy-selected 1,3,5-cycloheptatriene (CHT) and toluene (Tol) cations was investigated by imaging photoelectron photoion coincidence spectroscopy. In the measured Energy ranges of 10.30-11.75 eV for CHT and 11.45-12.55 eV for Tol, only the hydrogen atom loss channels open up, leading to C7H7+ from both molecular ions, which are both metastable at the H-loss threshold. Quantum chemical calculations showed that an interconversion of the molecular ions happens below the dissociation threshold. Therefore, a single statistical model was constructed to describe both systems simultaneously. We determined 0 K Appearance energies for the tropylium (Tr+) and benzyl (Bz+) fragment ions from CHT to be 9.520 ± 0.060 and 9.738 ± 0.082 eV and that from Tol to be 10.978 ± 0.063 and 11.196 ± 0.080 eV, respectively. Using the experimentally determined benzyl ion Appearance Energy, its 0 K heat of formation was calculated to be 937.9 ± 7.7 kJ mol-1. Finally, on the basis of this value and the recently determined benzyl ionization Energy, we point out discrepancies concerning the benzyl radical thermochemistry.
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Radical Thermometers, Thermochemistry, and Photoelectron Spectra: A Photoelectron Photoion Coincidence Spectroscopy Study of the Methyl Peroxy Radical.
Journal of Physical Chemistry Letters, 2018Co-Authors: Krisztina Voronova, Patrick Hemberger, Thomas Gerber, David L. Osborn, Krisztián G. Torma, Kent M. Ervin, Andras Bodi, Balint SztarayAbstract:We investigated the simplest alkylperoxy radical, CH3OO, formed by reacting photolytically generated CH3 radicals with O2, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck–Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization Energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH3OO generates the CH3+ fragment ion at the Appearance Energy of 11.164 ± 0.010 eV. Combining these two values with ΔfH0K°(CH3) yields ΔfH0K°(CH3OO) = 22.06 ± 0.97 kJ mol–1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH3OO breakdown diagram provides a molecular thermometer of the free radical’s internal temperature, which we measured to be 330 ± 30 K.
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Radical Thermometers, Thermochemistry, and Photoelectron Spectra: A Photoelectron Photoion Coincidence Spectroscopy Study of the Methyl Peroxy Radical
2017Co-Authors: Krisztina Voronova, Patrick Hemberger, Thomas Gerber, David L. Osborn, Krisztián G. Torma, Kent M. Ervin, Andras Bodi, Bálint SztárayAbstract:We investigated the simplest alkylperoxy radical, CH3OO, formed by reacting photolytically generated CH3 radicals with O2, using the new combustion reactions followed by photoelectron photoion coincidence (CRF-PEPICO) apparatus at the Swiss Light Source. Modeling the experimental photoion mass-selected threshold photoelectron spectrum using Franck–Condon simulations including transitions to triplet and singlet cationic states yielded the adiabatic ionization Energy of 10.265 ± 0.025 eV. Dissociative photoionization of CH3OO generates the CH3+ fragment ion at the Appearance Energy of 11.164 ± 0.010 eV. Combining these two values with ΔfH0K°(CH3) yields ΔfH0K°(CH3OO) = 22.06 ± 0.97 kJ mol–1, reducing the uncertainty of the previously determined value by a factor of 5. Statistical simulation of the CH3OO breakdown diagram provides a molecular thermometer of the free radical’s internal temperature, which we measured to be 330 ± 30 K
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bifurcated dissociative photoionization mechanism of acetic acid anhydride revealed by imaging photoelectron photoion coincidence spectroscopy
Physical Chemistry Chemical Physics, 2016Co-Authors: Krisztina Voronova, Patrick Hemberger, Andras Bodi, Krisztian G Torma, Chrissa Mozaffari M Easter, Balint SztarayAbstract:The fragmentation processes of internal Energy selected acetic acid anhydride cations, Ac2O+, were investigated by imaging photoelectron photoion coincidence (iPEPICO) spectroscopy. The first dissociation channel leads to the formation of CH3C(O)OCO+ (m/z = 87) by a CH3-loss. The 0 K Appearance Energy (E0) was determined to be 10.289 ± 0.010 eV, in excellent agreement with the G4-calculated 10.28 eV transition state (TS) Energy. Based on the thermochemical onset of CH3C(O)OCO+, a reverse barrier of 40 kJ mol−1 was found. The second dissociation channel leads to the formation of the acetyl cation, CH3CO+ (m/z = 43). The Appearance of trace amounts of acetone in the mass spectra, statistical modeling of the branching ratios, and quantum chemical calculations point to the existence of a post-transition-state bifurcation on the potential Energy surface and a single TS leading to multiple products. That is, at higher excess energies, the CH3-group may swerve back along an orbiting pathway to form the acetone cation by CO2-loss instead of leaving directly. The acetone cation thus formed is then energetic enough to lose a methyl group and yield the acetyl cation at a phenomenological E0 = 10.316 ± 0.015 eV. The acetyl cation, which dominates the breakdown diagram up to 16 eV photon Energy, is also formed by sequential CO2-loss from the CH3C(O)OCO+ intermediate at E0 = 10.53 ± 0.03 eV. The CH3+ (m/z = 15) fragment ion appears above 13 eV photon Energy. This species can be produced directly from the parent ion or via two sequential dissociation channels: by acetyl radical loss from the acetone cation or CO-loss from the acetyl cation.
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Vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet (VUV) photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence (i2PEPICO). A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum(SPES) of CH3O2 was obtained exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A′′ and a1A′overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy (AIE) of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracytheoretical data from the literature. The vertical ionization Energy of the b1A' electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.1548 ± 0.020 eV.
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vacuum ultraviolet photodynamics of the methyl peroxy radical studied by double imaging photoelectron photoion coincidences
Journal of Chemical Physics, 2020Co-Authors: Xiaofeng Tang, Krisztina Voronova, Balint Sztaray, Christa Fittschen, Xiaoxiao Lin, Weijun Zhang, Gustavo A Garcia, Jeanchristophe Loison, Laurent NahonAbstract:The vacuum ultraviolet photoionization of the methyl peroxy radical, CH3O2, and unimolecular dissociation of internal Energy selected CH3O2+ cations were investigated in the 9.7–12.0 eV Energy range by synchrotron-based double imaging photoelectron photoion coincidence. A microwave discharge flow tube was employed to produce CH3O2 via the reaction of methyl radicals (CH3) with oxygen gas. After identifying and separating the different sources of CH3+ from photoionization of CH3 or dissociative photoionization of CH3O2, the high resolution slow photoelectron spectrum (SPES) of CH3O2 was obtained, exhibiting two broad bands superimposed with a complex vibrational structure. The first band of the SPES is attributed to the X3A″ and a1A′ overlapped electronic states of CH3O2+ and the second is assigned to the b1A′ electronic state with the help of theoretical calculations. The adiabatic ionization Energy of CH3O2 is derived as 10.215 ± 0.015 eV, in good agreement with high-accuracy theoretical data from the literature. The vertical ionization Energy of the b1A′ electronic state is measured to be 11.5 eV and this state fully dissociates into CH3+ and O2 fragments. The 0 K adiabatic Appearance Energy (AE0K) of the CH3+ fragment ion is determined to be 11.15 ± 0.02 eV.
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dissociative photoionization of polycyclic aromatic hydrocarbon molecules carrying an ethynyl group
arXiv: Astrophysics of Galaxies, 2015Co-Authors: G Rouille, Xiaofeng Tang, Gustavo A Garcia, Serge A Krasnokutski, D Fulvio, C Jager, Thomas Henning, Laurent NahonAbstract:The life cycle of the population of interstellar polycyclic aromatic hydrocarbon (PAH) molecules depends partly on the photostability of the individual species. We have studied the dissociative photoionization of two ethynyl-substituted PAH species, namely, 9-ethynylphenanthrene and 1-ethynylpyrene. Their adiabatic ionization Energy and the Appearance Energy of fragment ions have been measured with the photoelectron photoion coincidence (PEPICO) spectroscopy technique. The adiabatic ionization Energy has been found at 7.84 +/- 0.02 eV for 9-ethynylphenanthrene and at 7.41 +/- 0.02 eV for 1-ethynylpyrene. These values are similar to those determined for the corresponding non-substituted PAH molecules phenanthrene and pyrene. The Appearance Energy of the fragment ion indicative of the loss of a H atom following photoionization is also similar for either ethynyl-substituted PAH molecule and its non-substituted counterpart. The measurements are used to estimate the critical Energy for the loss of a H atom by the PAH cations and the stability of ethynyl-substituted PAH molecules upon photoionization. We conclude that these PAH derivatives are as photostable as the non-substituted species in HI regions. If present in the interstellar medium, they may play an important role in the growth of interstellar PAH molecules.