Internal Methyl Rotation in the CH Stretching Overtone Spectra of Toluene-α-d2, -α-d1, and -d0

Kjaergaard, Henrik G.; Rong, Zimei; McAlees, Allan J.; Howard, Daryl L.; Henry, Bryan R.

doi:10.1021/jp000571d

Cited by 23 publications

(44 citation statements)

References 27 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…7,8 Later more complicated band profiles like the methyl band shape in molecules with low methyl rotational barriers were successfully simulated. [9][10][11][12] The relative intensities and spectral profiles within a given overtone could be calculated in good agreement with experiment with a relatively simple local mode model.…”

Section: Introductionsupporting

confidence: 53%

Absolute Intensities of CH Stretching Overtones in Alkenes

Rong

Henry²,

Robinson³

et al. 2005

J. Phys. Chem. A

Self Cite

View full text Add to dashboard Cite

We have measured the CH stretching vibrational spectrum of ethene gas in the regions corresponding to 1-5 quanta in the CH stretching vibration with Fourier transform infrared and conventional absorption spectroscopy and have determined the corresponding oscillator strengths. We have calculated the CH stretching vibrational oscillator strengths for a series of alkenes: ethene, propene, 1,3-butadiene, cis-2-butene, and trans-2-butene. The CH stretching intensities are calculated with a simple Morse oscillator local mode model for CH groups and with the harmonically coupled anharmonic oscillator local mode model for CH2 and CH3 groups. The local mode parameters, frequencies, and anharmonicities are obtained from experiments. The harmonic coupling coefficients and the dipole moment functions are calculated with a range of ab initio methods. These include self-consistent-field Hartree-Fock, density functional, correlated, and multireference theories, combined with basis sets ranging from double- to quadruple-zeta quality augmented with polarization and diffuse functions. Variation in calculated oscillator strengths with the choice of ab initio method is systematically studied and compared with observed intensities. From this comparison between the calculated and observed values, we can quantitatively understand the relative usefulness of various ab initio dipole moment functions in calculations of vibrational oscillator strength for alkenes.

show abstract

Section: Introductionsupporting

confidence: 53%

Absolute Intensities of CH Stretching Overtones in Alkenes

Rong

Henry²,

Robinson³

et al. 2005

J. Phys. Chem. A

Self Cite

View full text Add to dashboard Cite

show abstract

“…In previous work we have also simulated these profiles at ∆V CH ) 2-5 with a best fit procedure. 12 In the current work, we simulate the methyl band profiles of toluene at ∆v CH ) 3-6 with 340 points from ab initio calculations. In our previous work we could not reproduce the peak around 8600 cm -1 at ∆V CH ) 3.…”

Section: Resultsmentioning

confidence: 99%

“…In our previous work we could not reproduce the peak around 8600 cm -1 at ∆V CH ) 3. 12 We expanded the dipole moment function to the second order for the cross term in a Taylor series as a function of the displacement coordinates in our previous work. 12 Here we include the dipole moment function to the third-order mixed terms depending on two CH stretching coordinates such as q 1 q 2 2 and q 1 2 q 2 terms.…”

Section: Resultsmentioning

confidence: 99%

“…In our previous studies, we found the methyl overtone spectra of toluene, 4-methylpyridine, p-xylene, and m-xylene with quasi free rotors are very similar. [12][13][14]16 The methyl overtone spectrum of 2,6-difluorotoluene is different from the spectra of the above molecules although the torsional potential of 2,6-difluorotoluene is still relatively low. 11 Fermi resonance extensively exists in stretching overtone spectra and has been quantitatively analyzed in different approaches.…”

Section: Introductionmentioning

confidence: 88%

See 1 more Smart Citation

CH Stretching Overtone Spectra of Fluorine Substituted Toluenes

2003

Self Cite

View full text Add to dashboard Cite

We have measured and analyzed the vapor phase CH stretching overtone spectra of 3,5-difluorotoluene, 2,3,5,6-tetrafluorotoluene, and 2,3,4,5,6-pentafluorotoluene. The aryl bands are complex due to Fermi resonance. We have used a two-level system model to analyze the Fermi resonance within the aryl bands. The aryl regions of the overtone spectra are "corrected" for Fermi resonance and interpreted as uncoupled stretching oscillators. The methyl band profiles are complex due to the coupling between CH stretching and methyl torsion. The methyl band profiles are simulated with a CH stretching methyl torsion model. The CH stretching modes are described by a harmonically coupled anharmonic oscillator local mode model, and the methyl torsion is described by a rigid rotor model. Simulation parameters are obtained from ab initio calculations with the HF/6-31G(d) method. Relative intensities of aryl and methyl contributions in the CH stretching overtone spectra in the region ∆V CH ) 2-5 are measured and calculated for these molecules. We have found that the methyl bands of 3,5-difluorotoluene are very similar to corresponding bands in toluene, 4-methylpyridine, p-xylene, and m-xylene. The methyl bands of 2,3,5,6-tetrafluorotoluene and 2,3,4,5,6-pentafluorotoluene are virtually identical to those of 2,6-difluorotoluene. Thus, the main factor that determines the structure in methyl CH stretching overtone spectra of these molecules is the nature of the groups adjacent to the methyl group. The aryl bands of these molecules are primarily affected by the nearest substituents.

show abstract

“…However, these are only really useful for a few very low-lying states because of the inability of the method to correctly predict nodal structures in wave functions. On the other hand, adiabatic separation methods that have been applied for some smaller polyatomic clusters exist [7][8][9][10]. In particular, methods such as MULTIMODE by Bowman et al [11][12][13] and the harmonically coupled anharmonic oscillator methods by Kjaergarrd et al [8,[14][15][16][17][18] have been used to describe vibrationrotation-tunnelling (VRT) states in small polyatomic clusters including the water dimer.…”

Section: Introductionmentioning

confidence: 99%

An adiabatic model for calculating overtone spectra of dimers such as (H ₂ O) ₂

Tennyson

Barber

Kelly

2012

Phil. Trans. R. Soc. A.

View full text Add to dashboard Cite

The near-infrared and visible wavelength spectrum of the water dimer is considered to be the major contributor to the so-called water continuum at these wavelengths. However, theoretical models of this spectrum require the simultaneous treatment of both monomer and dimer excitations. A model for treating this problem is proposed which is based upon a Franck-Condon-like separation between the monomer and dimer vibrational motions. In this model, one of the monomers is treated as the chromophore and its absorption is assumed to be given by its, possibly perturbed, vibrational band intensity. The main computational issue is the treatment of separate monomer and dimer motions. Various approaches for obtaining dimer vibration-rotation tunnelling spectra that allow for monomer motion are explored. These approaches include ways of treating the adiabatic separation of dimer vibrational modes from monomer vibrational modes. We classify the adiabatic separation methods under four main approaches: namely fixed-geometry, freemonomer, perturbed-monomer and coupled-monomer methods. The latter being the most computationally expensive as the monomer wave functions are dependent on the dimer coordinates. For each of these approaches, expectation values over the full potential are calculated for the given monomer vibrational wave functions. Various full (named VAP 2pD in the text) and partial (VAP (+p)D) averaging techniques are outlined to calculate the vibrationally averaged, monomer state-dependent, dimer interaction potentials. The computational costs associated with application of these techniques to the water dimer are estimated and the prospects for full calculations based on this approach are assessed.

show abstract

Internal Methyl Rotation in the CH Stretching Overtone Spectra of Toluene-α-d₂, -α-d₁, and -d₀

Cited by 23 publications

References 27 publications

Absolute Intensities of CH Stretching Overtones in Alkenes

Absolute Intensities of CH Stretching Overtones in Alkenes

CH Stretching Overtone Spectra of Fluorine Substituted Toluenes

An adiabatic model for calculating overtone spectra of dimers such as (H ₂ O) ₂

Contact Info

Product

Resources

About

Internal Methyl Rotation in the CH Stretching Overtone Spectra of Toluene-α-d2, -α-d1, and -d0

Cited by 23 publications

References 27 publications

Absolute Intensities of CH Stretching Overtones in Alkenes

Absolute Intensities of CH Stretching Overtones in Alkenes

CH Stretching Overtone Spectra of Fluorine Substituted Toluenes

An adiabatic model for calculating overtone spectra of dimers such as (H 2 O) 2

Contact Info

Product

Resources

About

Internal Methyl Rotation in the CH Stretching Overtone Spectra of Toluene-α-d₂, -α-d₁, and -d₀

An adiabatic model for calculating overtone spectra of dimers such as (H ₂ O) ₂