Rotational and vibrational energy levels of methane calculated from a new potential energy surface

Nikitin, A.V.; Rey, M.; Tyuterev, Vladimir G.

doi:10.1016/j.cplett.2010.11.008

Cited by 102 publications

(137 citation statements)

References 45 publications

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“…A core correlation correction was added to the CCSD(T)/VQZ equilibrium geometry and the value, r e = 1.0862 ± 0.0005 Å, was retained. The PES of the second pair is the Nikitin, Rey, and Tuyterev (NRT) PES, 47 also calculated at the CCSD(T) level of theory, but with all electrons correlated and using a combination of the correlation consistent, polarized, core, valence quadruple zeta (ccpCVQZ or CVQZ in short) and augmented correlation consistent, polarized, core, valence quintuple zeta (aug-cc-pCV5Z or ACV5Z in short) basis sets. The latter basis set contains diffuse functions 48 and both basis sets possess core flexibility designed to take into account core and core-valence correlation.…”

Section: A Electronic Calculationsmentioning

confidence: 99%

Ab initio calculation of the rotational spectrum of methane vibrational ground state

Cassam-Chenaı̈

Liévin

2012

The Journal of Chemical Physics

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In a previous article we have introduced an alternative perturbation scheme to the traditional one starting from the harmonic oscillator, rigid rotator Hamiltonian, to find approximate solutions of the spectral problem for rotation-vibration molecular Hamiltonians. The convergence of our method for the methane vibrational ground state rotational energy levels was quicker than that of the traditional method, as expected, and our predictions were quantitative. In this second article, we study the convergence of the ab initio calculation of effective dipole moments for methane within the same theoretical frame. The first order of perturbation when applied to the electric dipole moment operator of a spherical top gives the expression used in previous spectroscopic studies. Higher orders of perturbation give corrections corresponding to higher centrifugal distortion contributions and are calculated accurately for the first time. Two potential energy surfaces of the literature have been used for solving the anharmonic vibrational problem by means of the vibrational mean field configuration interaction approach. Two corresponding dipole moment surfaces were calculated in this work at a high level of theory. The predicted intensities agree better with recent experimental values than their empirical fit. This suggests that our ab initio dipole moment surface and effective dipole moment operator are both highly accurate.

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Section: A Electronic Calculationsmentioning

confidence: 99%

Ab initio calculation of the rotational spectrum of methane vibrational ground state

Cassam-Chenaı̈

Liévin

2012

The Journal of Chemical Physics

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“…For CH 4 , the theoretical calculations are more difficult than for NH 3 and H 2 O, but many research groups are working on the problem [39,40]. As for ammonia, we expect that the theoretical groups will be able to make quantum number assignments in our spectra and will tune the potential energy surfaces to obtain better agreement with laboratory data, with the ultimate goal of obtaining a fully quantum mechanical line list comparable in quality to the BT2 list for water [6].…”

Section: Molecular Opacitiesmentioning

confidence: 99%

Molecular opacities for exoplanets

Bernath

2014

Phil. Trans. R. Soc. A.

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Spectroscopic observations of exoplanets are now possible by transit methods and direct emission. Spectroscopic requirements for exoplanets are reviewed based on existing measurements and model predictions for hot Jupiters and super-Earths. Molecular opacities needed to simulate astronomical observations can be obtained from laboratory measurements, ab initio calculations or a combination of the two approaches. This discussion article focuses mainly on laboratory measurements of hot molecules as needed for exoplanet spectroscopy.

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“…The potential energy surface (PES) in the Hamiltonian is the 10 th order, normal coordinate PES used in our previous calculation [29]. It has been derived from the Nikitin-Rey-Tuyterev (NRT) PES [22]. For details on the PES and on Watson µ-matrix expansion order, we refer the reader to Ref.…”

Section: Ab Initio Calculation Of Methane Rotation-vibration Eigenstatesmentioning

confidence: 99%

“…Proposed PES for methane include those of Gray and Robiette [15], Lee, Martin and Taylor [16], Schwenke and Partridge [17,18], Marquardt and Quack [19,20], Oyanagi et al [21], and more recently those of Nikitin, Rey and Tyuterev (NRT) [22] and Yurchenko et al. [25].…”

Section: Introductionmentioning

confidence: 99%

An improved third order dipole moment surface for methane

Cassam-Chenaı̈

Liévin

2013

Journal of Molecular Spectroscopy

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In a previous article a dipole moment surface (DMS) of full-electron, multi-reference configuration interaction (MRCI) quality was obtained and used to calculate the rotational spectrum of methane vibrational ground state, by means of a combination of the mean field configuration interaction method (VMFCI) with a generalized perturbation theory. The theoretical line intensities were matching the experimental ones obtained at the SOLEIL synchrotron well within experimental uncertainties.However, not all third order terms were included in this DMS. In the present work, additional DMS points have been calculated and fitted using a complete third order expansion. The new results give R-branch intensities systematically smaller by about 1 percent compared to those previously obtained by using the same ab initio method, so still within experimental errors. The relevance of this DMS to calculate intensities for excited vibrational states, in particular for the dyad, is addressed.

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Rotational and vibrational energy levels of methane calculated from a new potential energy surface

Cited by 102 publications

References 45 publications

Ab initio calculation of the rotational spectrum of methane vibrational ground state

Ab initio calculation of the rotational spectrum of methane vibrational ground state

Molecular opacities for exoplanets

An improved third order dipole moment surface for methane

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