Analytic calculations of anharmonic infrared and Raman vibrational spectra

Cornaton, Yann; Ringholm, Magnus; Louant, Orian; Ruud, Kenneth

doi:10.1039/c5cp06657c

Cited by 30 publications

(26 citation statements)

References 82 publications

(146 reference statements)

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“…These properties are respectively fifth-and sixth-order derivatives of the molecular energy, and the task of calculating these and the other properties used in this work is greatly simplified by the use of our recursive approach. In line with previous findings for IR and Raman spectroscopy, 34,39 we observe that the inclusion of anharmonicity has a larger effect on the frequencies than on the intensities, but we also see that the inclusion of combination and overtone bands using the anharmonic treatment can add important features that are not present at the double-harmonic level, such as the 8 1 11 1 combination peak at 2914 cm À1 for the ethane hyper-Raman spectrum. The anharmonic spectra are in qualitatively better agreement with experimental spectra, but for the systems in this work, a more detailed analysis of the improvements obtained by the inclusion of anharmonic effects is hindered by instrumental limitations leading to a significant level of noise in the experimental results.…”

Section: Summary and Concluding Remarkssupporting

confidence: 91%

“…The main improvement going to the anharmonic treatment lies in the correction of the vibrational frequencies, as was already shown in our previous work for the IR and Raman spectra. 39 However, including anharmonic corrections increases the difference in intensity between the strong 3 1 peak and the two other weak ones. In the experimental hyper-Raman spectrum, one feature appears larger than the experimental noise around 3000 cm À1 .…”

Section: Methanementioning

confidence: 99%

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Complete analytic anharmonic hyper-Raman scattering spectra

Cornaton

Ringholm

Ruud

2016

Phys. Chem. Chem. Phys.

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We present the first computational treatment of the complete second-order vibrational perturbation theory applied to hyper-Raman scattering spectroscopy. The required molecular properties are calculated in a fully analytic manner using a recently developed program [Ringholm, Jonsson and Ruud, J. Comp. Chem., 2014, 35, 622] that utilizes recursive routines. For some of the properties, these calculations are the first analytic calculations of their kind at their respective levels of theory. We apply this approach to the calculation of the hyper-Raman spectra of methane, ethane and ethylene and compare these to available experimental data. We show that the anharmonic corrections have a larger effect on the vibrational frequencies than on the spectral intensities, but that the inclusion of combination and overtone bands in the anharmonic treatment can improve the agreement with the experimental data, although the quality of available experimental data limits a detailed comparison.

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Section: Summary and Concluding Remarkssupporting

confidence: 91%

Section: Methanementioning

confidence: 99%

Complete analytic anharmonic hyper-Raman scattering spectra

Cornaton

Ringholm

Ruud

2016

Phys. Chem. Chem. Phys.

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“…For the vibration-rotation transition probabilities, we adopted the band strengths of Cornaton et al (2016), which were determined from ab initio calculations. They compared band strengths obtained with several different treatments of the geometric derivative tensors of the electric dipole moment.…”

Section: Ghzmentioning

confidence: 99%

Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei

Gorski,

Aalto,

Mangum

et al. 2021

Preprint

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We present the first search for the 5.29 GHz methanimine (CH 2 NH) 1 10 − 1 11 transition toward a sample of galaxy nuclei. We target seven galaxies that host compact obscured nuclei (CONs) with the Karl G. Jansky Very Large Array. These galaxies are characterized by Compton-thick cores. CH 2 NH emission is detected toward six CONs. The brightness temperatures measured toward Arp 220 indicate maser emission. Isotropic luminosities of the CH 2 NH transition, from all sources where it is detected, exceed 1 L and thus may be considered megamasers. We also detect formaldehyde (H 2 CO) emission toward three CONs. The isotropic CH 2 NH luminosities are weakly correlated with the infrared luminosity of the host galaxy and strongly correlated with OH megamaser luminosities from the same galaxies. Non-local thermodynamic equilibrium radiative transfer models suggest that the maser is pumped by the intense millimeter-to-submillimeter Our study suggests that CH 2 NH megamasers are linked to the nuclear processes within 100 pc of the Compton-thick nucleus within CONs.

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“…Indeed, anharmonicity of the electronic potential is often neglected and taken into account a posteriori using corrective factors that are empirically determined to match experimental measurements. More rigorously, explicit modeling of anharmonicity is also carried out using several methods including VSCF [20], VSCF-PT2 [21], cc- * julilam@ulb.ac.be † abdul-rahman.allouche@univ-lyon1.fr VSCF [22], VCI-P [23][24][25], VT2 [26], GVPT2 [27][28][29][30][31]. Because of the required high-level of ab-initio calculations, the current calculations are computationally demanding which hinders studying molecules of more than tens of atoms.…”

Section: Introductionmentioning

confidence: 99%

Combining Quantum Mechanics and Machine-Learning Calculations for Anharmonic Corrections to Vibrational Frequencies

Lam

Abdul-Al

Allouche

2020

J. Chem. Theory Comput.

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Several methods are available to compute the anharmonicity in semi-rigid molecules. However, such methods are not routinely employed yet because of their large computational cost, especially for large molecules. The potential energy surface is required and generally approximated by a quartic force field potential based on ab initio calculation, thus limiting this approach to medium-sized molecules. We developed a new, fast and accurate hybrid Quantum Mechanic/Machine learning (QM//ML) approach to reduce the computational time for large systems. With this novel approach, we evaluated anharmonic frequencies of 37 molecules thus covering a broad range of vibrational modes and chemical environments. The obtained fundamental frequencies reproduce results obtained using B2PLYP/def2tzvpp with a root-mean-square deviation (RMSD) of 21 cm −1 and experimental results with a RMSD of 23 cm −1 . Along with this very good accuracy, the computational time with our hybrid QM//ML approach scales linearly with N while the traditional full ab initio method scales as N 2 , where N is the number of atoms.

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Analytic calculations of anharmonic infrared and Raman vibrational spectra

Abstract: Using a recent recursive scheme for the calculation of high-order geometric derivatives of molecular properties, we present the first analytic calculations of infrared and Raman spectra including anharmonicity both in the vibrational frequencies and in the IR and Raman intensities.

Cited by 30 publications

References 82 publications

Complete analytic anharmonic hyper-Raman scattering spectra

Complete analytic anharmonic hyper-Raman scattering spectra

Discovery of Methanimine Megamasers Toward Compact Obscured Galaxy Nuclei

Combining Quantum Mechanics and Machine-Learning Calculations for Anharmonic Corrections to Vibrational Frequencies

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