High-Accuracy Extrapolated Ab Initio Thermochemistry of the Vinyl, Allyl, and Vinoxy Radicals

Tabor, Daniel P.; Harding, Michael E.; Ichino, Takatoshi; Stanton, John F.

doi:10.1021/jp302527n

Cited by 11 publications

(7 citation statements)

References 145 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…There are 12 determinations with individual contributions of 2% or more. The top contributor (7.0%) is the third law analysis of the equilibrium CH 2 CH 2 + Cl → CH 2 CH + HCl, based on kinetic measurements of Kaiser and Wallington and Russell et al Other top contributors, ranging individually between 5.9% and 2.0%, are extracted from state-of-the-art theoretical computations obtained at the HEAT 345-(Q) level of theory by Tabor et al, at the W4 and W4.2 level of theory by Karton et al, ,, and at the CCSD(T)-R12 level of theory by Aguilera-Iparraguirre et al, and inserted in the TN as TAE 0 (CH 2 CH), D 0 (CH 2 CH–H), D 0 (H–CHCH), D 0 (CH 2 C–H), and D (CH 2 CH–O).…”

Section: Results and Discussionmentioning

confidence: 99%

Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry

2015

View full text Add to dashboard Cite

Active Thermochemical Tables (ATcT) thermochemistry for the sequential bond dissociations of methane, ethane, and methanol systems were obtained by analyzing and solving a very large thermochemical network (TN). Values for all possible C-H, C-C, C-O, and O-H bond dissociation enthalpies at 298.15 K (BDE298) and bond dissociation energies at 0 K (D0) are presented. The corresponding ATcT standard gas-phase enthalpies of formation of the resulting CHn, n = 4-0 species (methane, methyl, methylene, methylidyne, and carbon atom), C2Hn, n = 6-0 species (ethane, ethyl, ethylene, ethylidene, vinyl, ethylidyne, acetylene, vinylidene, ethynyl, and ethynylene), and COHn, n = 4-0 species (methanol, hydroxymethyl, methoxy, formaldehyde, hydroxymethylene, formyl, isoformyl, and carbon monoxide) are also presented. The ATcT thermochemistry of carbon dioxide, water, hydroxyl, and carbon, oxygen, and hydrogen atoms is also included, together with the sequential BDEs of CO2 and H2O. The provenances of the ATcT enthalpies of formation, which are quite distributed and involve a large number of relevant determinations, are analyzed by variance decomposition and discussed in terms of principal contributions. The underlying reasons for periodic appearances of remarkably low and/or unusually high BDEs, alternating along the dissociation sequences, are analyzed and quantitatively rationalized. The present ATcT results are the most accurate thermochemical values currently available for these species.

show abstract

Section: Results and Discussionmentioning

confidence: 99%

Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry

2015

View full text Add to dashboard Cite

show abstract

“…More precise thermochemistry of the C 5 H 4 O molecule will soon be provided by HEAT calculations. 49,51 B. Photoionization Spectra and Dissociative Ionization. Dissociative Ionization of C 6 H 4 O 2 SO.…”

Section: Resultsmentioning

confidence: 99%

“…The preliminary results of Δ rxn H 298 (1) and Δ rxn H 298 (2) predict that the thermal decomposition of C 5 H 4 O to HCCCHCH 2 is about 40 kcal mol –1 more exothermic than decomposition to 2HCCH. More precise thermochemistry of the C 5 H 4 O molecule will soon be provided by HEAT calculations. , …”

Section: Resultsmentioning

confidence: 99%

Pyrolysis of Cyclopentadienone: Mechanistic Insights from a Direct Measurement of Product Branching Ratios

et al. 2015

Self Cite

View full text Add to dashboard Cite

The thermal decomposition of cyclopentadienone (C5H4═O) has been studied in a flash pyrolysis continuous flow microreactor. Passing dilute samples of o-phenylene sulfite (C6H4O2SO) in He through the microreactor at elevated temperatures yields a relatively clean source of C5H4═O. The pyrolysis of C5H4═O was investigated over the temperature range 1000-2000 K. Below 1600 K, we have identified two decomposition channels: (1) C5H4═O (+ M) → CO + HC≡C-CH═CH2 and (2) C5H4═O (+ M) → CO + HC≡CH + HC≡CH. There is no evidence of radical or H atom chain reactions. To establish the thermochemistry for the pyrolysis of cyclopentadienone, ab initio electronic structure calculations (AE-CCSD(T)/aug-cc-pCVQZ//AE-CCSD(T)/cc-pVQZ and anharmonic FC-CCSD(T)/ANO1 ZPEs) were used to find ΔfH0(C5H4═O) to be 16 ± 1 kcal mol(-1) and ΔfH0(CH2═CH-C≡CH) to be 71 ± 1 kcal mol(-1). The calculations predict the reaction enthalpies ΔrxnH0(1) to be 28 ± 1 kcal mol(-1) (ΔrxnH298(1) is 30 ± 1 kcal mol(-1)) and ΔrxnH0(2) to be 66 ± 1 kcal mol(-1) (ΔrxnH298(2) is 69 ± 1 kcal mol(-1)). Following pyrolysis of C5H4═O, photoionization mass spectrometry was used to measure the relative concentrations of HCC-CHCH2 and HCCH. Reaction 1 dominates at low pyrolysis temperatures (1000-1400 K). At temperatures above 1400 K, reaction 2 becomes the dominant channel. We have used the product branching ratios over the temperature range 1000-1600 K to extract the ratios of unimolecular rate coefficients for reactions 1 and 2 . If Arrhenius expressions are used, the difference of activation energies for reactions 1 and 2 , E2 - E1, is found to be 16 ± 1 kcal mol(-1) and the ratio of the pre-exponential factors, A2/A1, is 7.0 ± 0.3.

show abstract

“…The G4 results compared to in this experimental paper treat high-level correlation empirically, using parameters derived primarily from energy minima, not transition states. We are presently working to use advanced coupled cluster methods 34 to provide an ab initio determination of the barriers probed experimentally in this work. Note that our data are sensitive to the difference in the H + ketene barrier and the isomerization barrier, and the analysis relies on a C−Cl bond energy, so the robust conclusion is that the H + ketene barrier is 4.0 ± 0.5 kcal/mol above the isomerization barrier (44.6−40.6) if one assumes that the product branching is statistical.…”

Section: The Journal Of Physical Chemistry Amentioning

confidence: 99%

The Onset of H + Ketene Products from Vinoxy Radicals Prepared by Photodissociation of Chloroacetaldehyde at 157 nm

2016

View full text Add to dashboard Cite

We investigate the unimolecular dissociation of the vinoxy radical (CH2CHO) prepared with high internal energy imparted from the photodissociation of chloroacetaldehyde (CH2ClCHO) at 157 nm. Using a velocity map imaging apparatus, we measured the speed distribution of the recoiling chlorine atoms, Cl((2)P3/2) and Cl((2)P1/2), and derived from this the resulting distribution of kinetic energy, P(ET), imparted to the Cl + vinoxy fragments upon dissociation. Using conservation of energy, the distribution of kinetic energy was used to determine the total internal energy distribution in the radical. The P(ET) derived for the C-Cl bond fission presented in this work suggests the vinoxy radicals are mostly formed in the Ã state. We also took ion images at m/z = 42 and m/z = 15 to characterize the branching between the unimolecular dissociation channels of the vinoxy radical to H + ketene and methyl + CO products. Our results show a marked change in the branching ratio between the two channels from the previous study on the photodissociation of chloroacetaldehyde at 193 nm by Miller et al. (J. Chem. Phys., 2004, 121, 1830) in that the production of ketene is now favored over the production of methyl. To help analyze the data, we developed a model for the branching between the two channels that takes into account how the change in rotational energy en route to the products affects the vibrational energy available to surmount the barriers to the channels. The model predicts the portion of the C-Cl bond fission P(ET) that produces dissociative vinoxy radicals, then predicts the branching ratio between the H + ketene and CH3 + CO product channels at each ET. The model uses Rice-Ramsperger-Kassel-Marcus rate constants at the correct sums and densities of vibrational states while accounting for angular momentum conservation. We find that the predicted portion of the P(ET) that produces H + ketene products best fits the experimental portion (that we derive by taking advantage of conservation of momentum) if we use a barrier height for the H + ketene channel that is 4.0 ± 0.5 kcal/mol higher than the isomerization barrier en route to CH3 + CO products. Using the G4 computed isomerization barrier of 40.6 kcal/mol, this gives an experimentally determined barrier to the H + ketene channel of 44.6 kcal/mol. From these calculations, we also predict the branching ratio between the H + ketene and methyl + CO channels to be ∼2.1:1.

show abstract

High-Accuracy Extrapolated Ab Initio Thermochemistry of the Vinyl, Allyl, and Vinoxy Radicals

Cited by 11 publications

References 145 publications

Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry

Active Thermochemical Tables: Sequential Bond Dissociation Enthalpies of Methane, Ethane, and Methanol and the Related Thermochemistry

Pyrolysis of Cyclopentadienone: Mechanistic Insights from a Direct Measurement of Product Branching Ratios

The Onset of H + Ketene Products from Vinoxy Radicals Prepared by Photodissociation of Chloroacetaldehyde at 157 nm

Contact Info

Product

Resources

About