Erratum: “An assessment of theoretical procedures for the calculation of reliable free radical thermochemistry: A recommended new procedure” [J. Chem. Phys. <b>108</b>, 604 (1998)]

Mayer, Paul M.; Parkinson, C. J.; Smith, David M.; Radom, Leo

doi:10.1063/1.476372

Cited by 102 publications

(175 citation statements)

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“…In this context we note, see Table 1, that the available experimental f H 298 values for AN and PY1, 296 and 260 kcal mol −1 , are gratifyingly close to the calculated values, 298 and 260 kcal mol −1 , respectively. In the same vein, the f H 0 value of 100 kcal mol −1 for the severely spin-contaminated radical CH 2 C • -C N (ANR1 in Table 1, <S 2 > = 1.33) is virtually the same as the benchmark value, 100.2 kcal mol −1 , obtained in the elaborate theoretical study of spin-contaminated radicals by Mayer et al [16]. Finally we note that our mechanistic proposals of Scheme 7 remain essentially the same if the energy diagram were based upon the (relative) energies of the CBSB7 component of the method where spin-contamination is not an issue.…”

Section: Computational Aspectssupporting

confidence: 64%

“…For example, the acrylonitrile ion AN, the pyrimidine ion PY1, the vinylpyrimidine ion VP1 and the dimer ion D1 of Scheme 7 have <S 2 > values of 0.99, 1.29, 1.47 and 0.97, respectively. It is difficult to assess the effect of strong spincontamination on the errors in the CBS-QB3 derived energies but the incorporation of a spin-correction factor and the use of DFT derived geometries are expected to mitigate adverse effects [16]. In this context we note, see Table 1, that the available experimental f H 298 values for AN and PY1, 296 and 260 kcal mol −1 , are gratifyingly close to the calculated values, 298 and 260 kcal mol −1 , respectively.…”

Section: Computational Aspectsmentioning

confidence: 99%

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The acrylonitrile dimer ion: A study of its dissociation via self-catalysis, self-protonation and cyclization into the pyrimidine radical cation

Ervasti¹,

Jobst²,

Burgers³

et al. 2007

International Journal of Mass Spectrometry

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Large energy barriers prohibit the rearrangement of solitary acrylonitrile ions, CH 2 CHC N•+ , into their more stable hydrogen-shift isomers CH 2 C C NH•+ or CH CH-C NH •+ . This prompted us to examine if these isomerizations occur by self-catalysis in acrylonitrile dimer ions. Such ions, generated by chemical ionization experiments of acrylonitrile with an excess of carbon dioxide, undergo five dissociations in the s time frame, as witnessed by peaks at m/z 53, 54, 79, 80 and 105 in their metastable ion mass spectrum. Collision experiments on these product ions, deuterium labeling, and a detailed computational analysis using the CBS-QB3 model chemistry lead to the following conclusions: (i) the m/z 54 ions are ions CH 2 CHC NH + generated by self-protonation in ion-dipole stabilized hydrogen-bridged dimer ions [CH 2 CHC N· · ·H-C(C N)CH 2 ]•+ and [CH 2 CHC N· · ·H-C(H)C(H)C N]•+ ; the proton shifts in these ions are associated with a small reverse barrier; (ii) dissociation of the Hbridged ions into CH 2 C C NH•+ or CH CH-C NH •+ by self-catalysis is energetically feasible but kinetically improbable: experiment shows that the m/z 53 ions are CH 2 CHC N•+ ions, generated by back dissociation; (iii) the peaks at m/z 79, 80 and 105 correspond with the losses of HCN, C 2 H 2 and H• , respectively. The calculations indicate that these ions are generated from dimer ions that have adopted the (much more stable) covalently bound "head-to-tail" structure [CH 2 CHC N-C(H 2 )C(H)C N]•+ ; experiments indicate that the m/z 79 (C 5 H 5 N) and m/z 105 (C 6 H 6 N 2 ) ions have linear structures but the m/z 80 (C 4 H 4 N 2 ) ions consist of ionized pyrimidine in admixture with its stable pyrimidine-2-ylidene isomer. Acrylonitrile is a confirmed species in interstellar space and our study provides experimental and computational evidence that its dimer radical cation yields the ionized prebiotic pyrimidine molecule.

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Section: Computational Aspectssupporting

confidence: 64%

Section: Computational Aspectsmentioning

confidence: 99%

The acrylonitrile dimer ion: A study of its dissociation via self-catalysis, self-protonation and cyclization into the pyrimidine radical cation

Ervasti¹,

Jobst²,

Burgers³

et al. 2007

International Journal of Mass Spectrometry

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“…However, for more severely spincontaminated wave functions, they do not give reliable energies. The effect of spin contamination on computed energies is discussed in more detail by Mayer et al 16 In addition, for some of the transition states studied here that are nominally closedshell species, the restricted Hartree-Fock wave function was found to be unstable with respect to becoming unrestricted. In other cases, no transition state was found at the restricted Hartree-Fock level, or one was found that was qualitatively different from those found at higher levels or at the unrestricted Hartree-Fock level.…”

Section: Methodsmentioning

confidence: 99%

“…This is a variant of the CBS-Q method, in which the geometry optimization and frequency calculation are done at the QCISD/6-31G-(d) level of theory, and the larger QCISD energy calculation is replaced by a coupled-cluster (CCSD(T)) calculation. This procedure was shown by Mayer et al 16 to give more accurate energies than the G-2 or CBS-Q methods for spin-contaminated radical species. In the CBS-RAD method, we used unrestricted wave functions for all species, including nominally closed-shell species.…”

Section: Methodsmentioning

confidence: 99%

“…Of course, the restricted calculations could be replaced with their unrestricted counterparts, but then it is questionable whether the result can still be called a CBS-Q or G-2 calculation. Therefore, the CBS-RAD method, recommended by Mayer et al 16 for computing highaccuracy energies of free radicals, was also applied to all of the molecules and transition states considered here. This is a variant of the CBS-Q method, in which the geometry optimization and frequency calculation are done at the QCISD/6-31G-(d) level of theory, and the larger QCISD energy calculation is replaced by a coupled-cluster (CCSD(T)) calculation.…”

Section: Methodsmentioning

confidence: 99%

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Reactions in the Al−H−Cl System Studied by ab Initio Molecular Orbital and Density Functional Methods

Swihart

Catoire

2000

J. Phys. Chem. A

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High-level ab initio quantum chemical calculations have been used to investigate possible reactions in the Al-H-Cl system. Transition states or barrierless reaction paths have been identified for essentially all feasible reactions in this system involving a single aluminum atom. Structures, energies, and vibrational frequencies for reactants, products, and transition states in this system are presented. These results provide a basis for the estimation of reaction rate parameters for this system using transition state theory and related unimolecular reaction rate theories and thereby construct a reaction mechanism useful for detailed chemical kinetic modeling of aluminum combustion in HCl and chemical vapor deposition using AlCl 3 in H 2 . In the few cases where previous experimental or theoretical results have been published, the present work is consistent with previous work.

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Keto-enol tautomerism and dissociation of ionized acetaldehyde and vinyl alcohol. A G2 Molecular Orbital Study

Bertrand

Bouchoux

1998

Rapid Commun. Mass Spectrom.

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Both studies 1,2 agree qualitatively in the estimates of the various critical energies separating each isomer and the dissociation products. However discrepancies of no less than 50 kJ/mol were apparent for some elementary steps, particularly hydrogen atom migrations. Furthermore, conflicting conclusions were drawn concerning the nature of the energy determining step for dissociation 3 of 1 Á . To clarify these questions, in view of the moderate size of this system, it was of interest to reinvestigate the energetic of reactions of Scheme 1 using a more sophisticated theoretical method such as the G2 theory. 4 COMPUTATIONAL SECTIONIt seems well established that accurate heats of formation of open-shell systems can be attained at the G2 level of theory 4a for species with low spin contamination. 5 Standard G2 theory employs a geometry optimized at the MP2(full)/ 6-31G(d) level and a scaled HF/6-31G(d) ZPE. A base energy calculated at the MP4/6-311G(d,p) level is corrected by several additivity approximations to QCISD(T) and to 6-311G(3df,2p) basis set. In an attempt to account for residual basis set deficiencies, G2 theory introduces higherlevel corrections (HLC) that depends on the number of paired and unpaired electrons. In the more economical G2(MP2) approach, the basis set-extension energy corrections are obtained at the 2nd order Molle-Plesset level.

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Erratum: “An assessment of theoretical procedures for the calculation of reliable free radical thermochemistry: A recommended new procedure” [J. Chem. Phys. 108, 604 (1998)]

Cited by 102 publications

References 0 publications

The acrylonitrile dimer ion: A study of its dissociation via self-catalysis, self-protonation and cyclization into the pyrimidine radical cation

The acrylonitrile dimer ion: A study of its dissociation via self-catalysis, self-protonation and cyclization into the pyrimidine radical cation

Reactions in the Al−H−Cl System Studied by ab Initio Molecular Orbital and Density Functional Methods

Keto-enol tautomerism and dissociation of ionized acetaldehyde and vinyl alcohol. A G2 Molecular Orbital Study

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