Vibrational overtone spectroscopy and internal dynamics in gaseous nitromethane NO2CH2D

Cavagnat, D.; Lespade, L.

doi:10.1063/1.476382

Cited by 14 publications

(17 citation statements)

References 50 publications

(63 reference statements)

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“…Palmö, Mirkin, and Krimm have found that CC force constants in neopentane depend on the methyl torsional angle, and that CH force constants are coupled to CC force constants. The coupling between CH vibrational frequencies and methyl torsional angle can also be seen in the dependence of local mode parameters ω and ω x on φ given by eqs 8 and 9 and the parameters δ ω and δ ω x (Table ). − The change in local mode transition frequencies resulting from varying φ from 60° to 45° are calculated using the data in Table and eqs 5, 8, and 9. As the torsional angle changes from φ = 60° to 45°, the local mode transition frequency increases.…”

Section: Resultsmentioning

confidence: 99%

“…Coupling between Stretching and Torsional Motions. CH stretching modes couple to torsional modes through the dependence of ω and ω x on the dihedral (torsional) angle φ. − In the M(CH 3 ) 4 homologues this dependence can be approximated as a cosine squared function where δ ω = ω(0°) − ω(60°) in which ω(60°) and ω(0°) are the local mode frequencies in the staggered and eclipsed conformers, respectively. The values of ω(60°) and ω(0°) are calculated using the method of Low and Kjaergaard where, in our case, the ab initio value of ω(60°) is scaled to be identical to the experimentally obtained value of ω.…”

Section: Theory and Calculationsmentioning

confidence: 99%

See 1 more Smart Citation

Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Petryk

Henry

2002

J. Phys. Chem. A

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A comparison of the CH vibrational overtone spectra of vapor phase neopentane-d 0 (C(CH3)4), -d 6 (C(CH3)2(CD3)2), and -d 9 (C(CH3)(CD3)3) and tetramethylsilane (TMS) in the frequency range Δv CH = 4−8 (10 800−18 200 cm-1) has revealed pronounced differences between the spectra of TMS and the neopentanes, and subtle differences among the spectra of the neopentanes. These spectral differences are interpreted as a manifestation of geometry and vibrational frequency dependent differences in coupling efficiencies that facilitate the de-excitation of local modes of vibration via IVR. Fermi resonance plays a key role in this coupling. Some of the states are perturbed by through space coupling (a collision-like van der Waals interaction) that can facilitate IVR. The normal modes of vibration, which are implicated in Fermi resonance of the neopentanes and TMS, have been calculated ab initio using density functional theory and are shown to be affected by through space interactions.

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Section: Resultsmentioning

confidence: 99%

Section: Theory and Calculationsmentioning

confidence: 99%

Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Petryk

Henry

2002

J. Phys. Chem. A

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“…Such an internal rotation is strongly coupled with many other vibrational motions, particularly with the methyl CH stretching vibrations. ,,, The conformation-dependent CH vibrators thus constitute a unique probe for obtaining detailed microscopic information about the structure and internal dynamics of the material. As shown for similar molecules, the complex features observed in fundamental infrared and Raman spectra of the methyl CH stretching vibrations are conserved in the excited states but are often perturbed by the presence of strong CH stretch−bend Fermi resonance phenomena, leading to internal vibrational energy redistribution (IVR). − …”

Section: Introductionmentioning

confidence: 98%

Methyl Group Internal Rotation Dynamics: Overtone Study of Gaseous Methylpyridine-2-αd₂ and -3-αd₂

et al. 2000

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Conventional infrared absorption and Raman spectroscopy have been used to record the vapor phase spectra of methylpyridine-2-Rd 2 ,6-d 1 , methylpyridine-2-Rd 2 , and methylpyridine-3-Rd 2 ,-d 4 in the ∆V CH ) 1-4 regions. The spectra are analyzed with a theoretical model that takes into account, in the adiabatic approximation, the coupling between the internal rotation of the methyl group and the methyl CH stretching vibration. The principal parameters used in this model have been determined by ab initio calculations at the HF/6-31G** level of theory. A good agreement between experimental and calculated spectra is found. This indicates that this coupling is at the origin of the majority of the observed spectral profiles. A comparison of these results with those previously obtained for similar methylated molecules reveals that the change in type and size of the barrier to internal methyl rotation is at the origin of significant spectral differences. These changes are particularly important for methylpyridine-2-Rd 2 , revealing that the methyl group experiences increasingly different internal dynamics with increasing energy. These spectral changes can be well explained by the deformation of the effective internal rotation potential in the vibrational excited states. The overtone spectra of the aryl CD stretching of methylpyridine-3-Rd 2 ,-d 4 have also been studied.

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“…Cavagnat et al have successfully simulated the methyl profiles in the spectra of nitromethanes, − toluenes , and methylpyridine-4-α- d 2 , all molecules with small 6-fold torsional barriers. In the molecules with CH 3 groups they considered the effect of Fermi resonance between CH stretching and HCH bending vibrations.…”

Section: Introductionmentioning

confidence: 99%

“…This seemed to improve the agreement in the fundamental and first overtone regions. They used an ab initio calculated dipole moment function expanded in both the CH stretching displacement coordinates and torsional angle. − Recently, Cavagnat et al also simulated methyl band profiles in the Δ v CH = 1−4 spectra of methylpyridine-2-α- d 2 and methylpyridine-3-α- d 2 . These molecules have 3-fold torsional barrier heights of 90 and 50 cm -1 , respectively.…”

Section: Introductionmentioning

confidence: 99%

Internal Methyl Rotation in the CH Stretching Overtone Spectra of ortho-, meta-, and para-Xylene

Rong

Kjaergaard

2002

J. Phys. Chem. A

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The room-temperature vapor phase overtone spectra of o-, m-, and p-xylene have been recorded in the CH stretching region corresponding to Δv CH = 2−6 with conventional near-infrared spectroscopy (Δv CH = 2 and 3), intracavity titanium:sapphire (Δv CH = 4 and 5) and dye laser photoacoustic spectroscopy (Δv CH = 6). Absolute oscillator strengths have been measured from the conventional spectra and relative oscillator strengths within a given overtone from the conventional and photoacoustic spectra. The aryl region of the spectra can be interpreted simply in terms of a number of nonequivalent and independent local modes. The methyl region of the spectra is more complex. The methyl band profiles in the overtone spectra of m-xylene and p-xylene are very similar to each other and to that of toluene and differ significantly from the methyl band profiles in the spectra of o-xylene. We use a simple anharmonic oscillator local mode model with ab initio calculated dipole moment functions to calculate oscillator strengths of the aryl transitions. The methyl band profiles are simulated on the basis of a model that incorporates the harmonically coupled anharmonic oscillator local mode model for the CH stretching modes and a rigid rotor basis for the methyl internal rotation (torsion). The model parameters are calculated ab initio. The dipole moment function is expressed in a series expansion in both the CH displacement coordinate and the torsional angle whereas the frequency, anharmonicity, and torsional potential are expressed in Fourier series of the torsional angle. The difference in the methyl band profiles in o-xylene, and in m- and p-xylene are ascribed mainly to differences in the torsional potential and the dipole moment function. Our simulations have successfully reproduced the methyl band profiles in the xylene spectra and the relative aryl to methyl intensities.

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Vibrational overtone spectroscopy and internal dynamics in gaseous nitromethane NO2CH2D

Cited by 14 publications

References 50 publications

Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Methyl Group Internal Rotation Dynamics: Overtone Study of Gaseous Methylpyridine-2-αd₂ and -3-αd₂

Internal Methyl Rotation in the CH Stretching Overtone Spectra of ortho-, meta-, and para-Xylene

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Vibrational overtone spectroscopy and internal dynamics in gaseous nitromethane NO2CH2D

Cited by 14 publications

References 50 publications

Through Space Coupling and Fermi Resonances in Neopentane-d0, -d6, -d9, and Tetramethylsilane

Through Space Coupling and Fermi Resonances in Neopentane-d0, -d6, -d9, and Tetramethylsilane

Methyl Group Internal Rotation Dynamics: Overtone Study of Gaseous Methylpyridine-2-αd2 and -3-αd2

Internal Methyl Rotation in the CH Stretching Overtone Spectra of ortho-, meta-, and para-Xylene

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Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Through Space Coupling and Fermi Resonances in Neopentane-d₀, -d₆, -d₉, and Tetramethylsilane

Methyl Group Internal Rotation Dynamics: Overtone Study of Gaseous Methylpyridine-2-αd₂ and -3-αd₂