Coherence-converted population transfer FTMW-IR double resonance spectroscopy of CH3OD in the OD-stretch region

Twagirayezu, Sylvestre; Perry, David S.; Neill, Justin L.; Muckle, Matt T.

doi:10.1016/j.jms.2010.05.003

Cited by 5 publications

(2 citation statements)

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“…The rovibrational spectroscopy of methanol has been the subject of numerous experimental [1][2][3][4][5][6][7][8] and theoretical papers [9][10][11][12][13][14][15][16][17], with a focus on the facile internal torsional motion. Signatures of that motion in the vibrational spectrum of the fundamentals and overtones of the CH and OHstretch modes have been reported in recent experiments.…”

Section: Introductionmentioning

confidence: 99%

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Bowman

2013

Molecular Physics

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An accurate, ab initio potential energy surface (PES) is reported for CH 3 OH including the bound region as well as the barrierless dissociation to CH 3 + OH. The surface is a linear least-squares fit to a total of 45,199 ab initio energies, most of which were computed using CCSD(T)-F12b/aug-cc-pVDZ theory and a small number using CASPT2/aug-cc-pVDZ theory. The latter set was done in the multi-reference region of the PES in order to obtain a realistic description of the OH-CH 3 interaction in the near asymptotic region. The geometries and harmonic frequencies of the stationary points agree very well with direct CCSD(T)-F12b calculations. The three-fold barrier to internal rotation of CH 3 OH is also accurately described by the PES. The zero-point energies of methanol and CH 3 + OH are determined by Diffusion Monte Carlo calculations. The D 0 dissociation energy is 90.1 kcal/mol, in very good agreement with the recent IUPAC evaluation [Ruscic et al., J. Phys. Chem. Ref. Data 34, 573 (2005)] result of 90.25 kcal/mol. Keywords: potential energy surface; ab initio; methanol dissociation energy IntroductionThe rovibrational spectroscopy of methanol has been the subject of numerous experimental [1-8] and theoretical papers [9-17], with a focus on the facile internal torsional motion. Signatures of that motion in the vibrational spectrum of the fundamentals and overtones of the CH and OHstretch modes have been reported in recent experiments.Methanol is a challenging system for an ab initio approach, owing both to the dimensionality of the configuration space (12 vibrational degrees of freedom) and also the need to accurately describe the low-barrier torsional motion. High-level theoretical work on the vibration/torsion energies of CH 3 OH has made use of ab initio-based force fields and a potential that are limited to the region of the minimum of the potential [11][12][13][14][15][16][17]. The most recent of these [15] used electronic energies obtained using coupled-clustersingles-doubles and perturbative treatment of triples excitations (CCSD(T)) theory with large polarised basis sets, i.e. aug-cc-pVTZ. The limited PES we developed [15] was a fit to 19,315 CCSD(T)/aVTZ energies. That PES was used in MULTIMODE-Reaction Path calculations [15,16] of numerous low-lying vibration/torsion energies, which are in good agreement with experiment.That PES does not describe dissociation or near dissociation to any fragments, in particular to CH 3 + OH. These are among the dominant products of the thermal decomposition of CH 3 OH. That decomposition as well as the recombination of CH 3 + OH are important processes in combustion chemistry and have been studied over a range of

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Section: Introductionmentioning

confidence: 99%

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Bowman

2013

Molecular Physics

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“…In terms of the level structure, it includes interactions of the ν 2 and ν 9 vibrations with torsionally excited states built on ν 3 . A first principles full dimensional treatments of the methanol tunneling splittings by Sibert and Castillo-Chara included all of the other nearly resonant vibrational states, including the six binary CH bend combination bands that have been shown to interact strongly with the CH fundamentals. ,,, Each of these two treatments and model II yield different discrepancies relative to experiment (Table ), but overall, the agreement with experiment is comparable.…”

Section: Discussion and Conclusionmentioning

confidence: 99%

Torsion–Inversion Tunneling Patterns in the CH-Stretch Vibrationally Excited States of the G₁₂ Family of Molecules Including Methylamine

2013

Self Cite

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Two torsion-inversion tunneling models (models I and II) are reported for the CH-stretch vibrationally excited states in the G12 family of molecules. The torsion and inversion tunneling parameters, h(2v) and h(3v), respectively, are combined with low-order coupling terms involving the CH-stretch vibrations. Model I is a group theoretical treatment starting from the symmetric rotor methyl CH-stretch vibrations; model II is an internal coordinate model including the local-local CH-stretch coupling. Each model yields predicted torsion-inversion tunneling patterns of the four symmetry species, A, B, E1, and E2, in the CH-stretch excited states. Although the predicted tunneling patterns for the symmetric CH-stretch excited state are the same as for the ground state, inverted tunneling patterns are predicted for the asymmetric CH-stretches. The qualitative tunneling patterns predicted are independent of the model type and of the particular coupling terms considered. In model I, the magnitudes of the tunneling splittings in the two asymmetric CH-stretch excited states are equal to half of that in the ground state, but in model II, they differ when the tunneling rate is fast. The model predictions are compared across the series of molecules methanol, methylamine, 2-methylmalonaldehyde, and 5-methyltropolone and to the available experimental data.

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On the molecular structure of HOOO

McCarthy

Lattanzi

Kokkin

et al. 2012

The Journal of Chemical Physics

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The molecular structure of trans, planar hydridotrioxygen (HOOO) has been examined by means of isotopic spectroscopy using Fourier transform microwave as well as microwave-millimeter-wave double resonance techniques, and high-level coupled cluster quantum-chemical calculations. Although this weakly bound molecule is readily observed in an electrical discharge of H(2)O and O(2) heavily diluted in an inert buffer gas, we find that HOOO can be produced with somewhat higher abundance using H(2) and O(2) as precursor gases. Using equal mixtures of normal and (18)O(2), it has been possible to detect three new isotopic species, H(18)OOO, HO(18)O(18)O, and H(18)O(18)O(18)O. Detection of these species and not others provides compelling evidence that the dominant route to HOOO formation in our discharge is via the reaction OH + O(2) → HOOO. By combining derived rotational constants with those for normal HOOO and DOOO, it has been possible to determine a fully experimental (r(0)) structure for this radical, in which all of the structural parameters (the three bond lengths and two angles) have been varied. This best-fit structure possesses a longer central O-O bond (1.684 Å), in agreement with earlier work, a markedly shorter O-H bond distance (0.913 Å), and a more acute [angle]HOO angle (92.4°) when compared to equilibrium (r(e)) structures obtained from quantum-chemical calculations. To better understand the origin of these discrepancies, vibrational corrections have been obtained from coupled-cluster calculations. An empirical equilibrium (r(e) (emp)) structure, derived from the experimental rotational constants and theoretical vibrational corrections, gives only somewhat better agreement with the calculated equilibrium structure and large residual inertial defects, suggesting that still higher order vibrational corrections (i.e., γ terms) are needed to properly describe large-amplitude motion in HOOO. Owing to the high abundance of this oxygen-chain radical in our discharge expansion, a very wide spectral survey for other oxygen-bearing species has been undertaken between 6 and 25 GHz. Only about 50% of the observed lines have been assigned to known hydrogen-oxygen molecules or complexes, suggesting that a rich, unexplored oxygen chemistry awaits detection and characterization. Somewhat surprisingly, we find no evidence in our expansion for rotational transitions of cis HOOO or from low-lying vibrationally excited states of trans HOOO under conditions which optimize its ground state lines.

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Coherence-converted population transfer FTMW-IR double resonance spectroscopy of CH3OD in the OD-stretch region

Cited by 5 publications

References 37 publications

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Torsion–Inversion Tunneling Patterns in the CH-Stretch Vibrationally Excited States of the G₁₂ Family of Molecules Including Methylamine

On the molecular structure of HOOO

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Coherence-converted population transfer FTMW-IR double resonance spectroscopy of CH3OD in the OD-stretch region

Cited by 5 publications

References 37 publications

Full-dimensional, ab initio potential energy surface for CH3OH → CH3+OH

Full-dimensional, ab initio potential energy surface for CH3OH → CH3+OH

Torsion–Inversion Tunneling Patterns in the CH-Stretch Vibrationally Excited States of the G12 Family of Molecules Including Methylamine

On the molecular structure of HOOO

Contact Info

Product

Resources

About

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Full-dimensional, ab initio potential energy surface for CH₃OH → CH₃+OH

Torsion–Inversion Tunneling Patterns in the CH-Stretch Vibrationally Excited States of the G₁₂ Family of Molecules Including Methylamine