Quantum-Chemical calculations on molecules of astrochemical interest

Botschwina, Peter; Seeger, S.; Horn, Matthias; Flügge, J.; Oswald, M.; Mladenowić, M.; Höper, U.; Oswald, Rainer; Schick, Eginhard

doi:10.1063/1.46614

Cited by 27 publications

(74 citation statements)

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“…The corresponding frequency differences ( GHFF -ab initio ) for modes 1 to 6 of CH 3 Cl, using the MP4 results of Harris (5), are ϩ3, Ϫ1, ϩ16, Ϫ10, Ϫ2, and 0 cm Ϫ1 , respectively. Harmonic vibration frequencies (but not force constants) are available also from a CEPA-1 calculation (6). Comparison with the latter shows a similar close agreement, yielding differences of ϩ4, 0, ϩ9, Ϫ4, Ϫ8, and Ϫ7 cm Ϫ1 .…”

Section: Ghff Of Methyl Chloridesupporting

confidence: 54%

“…(1)(2)(3)(4)(5)(6)) and references cited therein), it is only comparatively recently that the anharmonic corrections required for comparison with empirical vibration frequencies have been quantitatively understood (7,8). These advances in the understanding of the vibrational anharmonicities (including Fermi resonance effects) for the methyl halides (7)(8)(9)(10) and the large number of new and improved high-resolution spectroscopic data now available (in particular axial centrifugal distortion constants D K ) make a recalculation of the empirical general harmonic force field (GHFF) of methyl chloride appropriate at this time.…”

Section: Introductionmentioning

confidence: 98%

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The General Harmonic Force Field of Methyl Chloride

Black

Law

2001

Journal of Molecular Spectroscopy

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Section: Ghff Of Methyl Chloridesupporting

confidence: 54%

Section: Introductionmentioning

confidence: 98%

The General Harmonic Force Field of Methyl Chloride

Black

Law

2001

Journal of Molecular Spectroscopy

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“…Several more extensive ab initio calculations on, among others, reactions (2) and (3) restricted to stationary points have been reported: while Glukhovtsev et al [64,65] made use of the G2(+ ) level of theory, Botschwina, [66] Schmatz et al, [67] and Parthiban et al [68] employed coupled cluster methods. The system: F À + CH 3 Cl was also studied by Botschwina et al [69] A recent CCSD(T) study with large basis sets, performed by Gonzales et al, [70] deals with the systems F À + CH 3 X (with X = F, Cl, CN, OH, SH, NH 2 , PH 2 ). Four-dimensional analytical representations of CCSD(T) PESs have been provided for the systems Cl À + CH 3 Cl [71,72] and Cl À + CH 3 Br.…”

Section: Full-dimensional Potential Energy Surfaces Based On Low-levementioning

confidence: 97%

Quantum Dynamics of Gas‐Phase S_N2 Reactions

Schmatz

2004

ChemPhysChem

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Understanding the state-resolved dynamics of elementary chemical reactions involving polyatomic molecules, such as the well-known reaction mechanism of nucleophilic bimolecular substitution (SN2), is one of the principal goals in chemistry. In this Review, the progress in the quantum mechanical treatment of SN2 reactions in the gas phase is reviewed. The potential energy profile of this class of reactions is characterized by two relatively deep wells, which correspond to pre- and post-reaction chargedipole complexes. As a consequence, the complex-forming reaction is dominated by Feshbach resonances. Calculations in the energetic continuum constitute a major challenge because the high density of resonance states imposes considerable requirements on the convergence and the energetic resolution of the scattering data. However, the effort is rewarding because new insights into the details of multimode quantum dynamics of elementary chemical reactions can be obtained.

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“…Owing mainly to the neglect of core-valence and core-core correlation eects, this value appears to be slightly too long. The same sort of calculations for CH 3 Cl yields R e (CeCl) 1.7821 A Ê , r e (CeH) 1.0853 A Ê , and b e (HeCeCl) 108.43°, which can be compared with our recommended equilibrium geometry values [6] of 1.7762 A Ê , 1.0836 A Ê and 108.58°. Assuming the same error to hold for the CCSD(T) value of the CCl distance at the saddle point, we arrive at R s 2.301 A Ê .…”

mentioning

confidence: 97%

“…The ®rst one (basis A) consists of 248 contracted Gaussian-type orbitals (cGTOs) and is the same as used in our previous investigation of the reaction F A + CH 3 Cl ® FCH 3 + Cl A [6]. It is comprised of the (s, p, d, f) functions of the aug-cc-pVQZ basis of Dunning and coworkers [7±9] for carbon and chlorine.…”

mentioning

confidence: 99%

The saddle point of the nucleophilic substitution reaction Cl − + CH 3 Cl: results of large-scale coupled cluster calculations

Botschwina

1998

Theoretical Chemistry Accounts: Theory, Computation, and Modeli

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On the basis of large-scale coupled cluster calculations including connectedz triple substitutions in a perturbative way, the geometrical parameters of the D 3h saddle point of the Walden inversion reaction Cl A + CH 3 Cl¢ ® ClCH 3 + Cl¢ A are predicted to be R s (CeCl) 2.301 A Ê and r s (CeH) 1.069 A Ê . The barrier height with respect to the reactants is recommended to be 11.5 1.0 kJ mol A1 . Connected triple substitutions lower the barrier height by almost a factor of 2, but have very little in¯uence on the geometric structure of the saddle point. Key words: S N 2 nucleophilic substitution reactions ± Coupled cluster calculationsThe nucleophilic substitution (S N 2) reaction Cl A + CH 3 Cl¢ ® ClCH 3 + Cl 1A is one of the fundamental reactions in physical organic chemistry and has been the subject of numerous experimental and theoretical studies (see Ref.[1] for a review). In a very recent paper by Clary and Palma [2] it has been shown, on the basis of three-dimensional quantum scattering calculations within the rotating bond approximation, that the length of the CeCl bond R s at the saddle point has a particularly pronounced eect on the reaction probabilities. It is obvious from Table 1 of Ref.[2] that this quantity is still not too well known from quantum chemistry calculations. Likewise, the height of the barrier with respect to the energy of the reactants has not yet been reliably established to an accuracy of better than 3 kJ mol A1 . It is the main purpose of this note to present accurate values for both R s and the barrier height (BH).We mainly make use of coupled cluster theory with single and double excitation operators plus a perturbative treatment of the eects of connected triple substitutions by means of the variants CCSD(T) [3] and CCSD-T [4]. All valence electrons are correlated in the calculations which were carried out with the MOLPRO suite of programs [5]. Two dierent basis sets were employed for the determination of the geometric structure

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Quantum-Chemical calculations on molecules of astrochemical interest

Cited by 27 publications

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The General Harmonic Force Field of Methyl Chloride

The General Harmonic Force Field of Methyl Chloride

Quantum Dynamics of Gas‐Phase S_N2 Reactions

The saddle point of the nucleophilic substitution reaction Cl − + CH 3 Cl: results of large-scale coupled cluster calculations

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Quantum-Chemical calculations on molecules of astrochemical interest

Cited by 27 publications

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The General Harmonic Force Field of Methyl Chloride

The General Harmonic Force Field of Methyl Chloride

Quantum Dynamics of Gas‐Phase SN2 Reactions

The saddle point of the nucleophilic substitution reaction Cl − + CH 3 Cl: results of large-scale coupled cluster calculations

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Quantum Dynamics of Gas‐Phase S_N2 Reactions