The role of electron correlation on calculated XH-stretching vibrational band intensities

Kjaergaard, Henrik G.; Daub, Christopher D.; Henry, Bryan R.

doi:10.1080/00268979709482601

Cited by 29 publications

(52 citation statements)

References 45 publications

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“…The conclusion from these studies was that the above-mentioned property was the steepness of the repulsive wall of the potential in agreement with other studies (Medvedev, 1984(Medvedev, , 1985b(Medvedev, , 1998Nikitin et al, 1993). The immediate outcome of this result was a straightforward explanation to the so-called chemical transferability of the CH higher-overtone intensities observed in rows of similar compounds [see, for example, Ahmed and Henry (1987); ; ; Lange et al (2001); Lehmann and Smith (1990); Lewerenz and Quack (1986); Phillips et al (1998); Vaida et al (2008)] and insensitivity of the intensities to electron correlations (Kjaergaard et al, 1997Schwenke and Partridge, 2000). [On the contrary, Quack and co-workers (Ha et al, 1990(Ha et al, , 1992Quack, 1986, 1988) found low sensitivity of overtone intensities to the potential, see Sec.…”

Section: Introductionsupporting

confidence: 83%

“…III B. Such calculations are easy to perform because electron correlation is less significant in the region of strong interatomic repulsion (Kjaergaard et al, 1997). Examples can be found in Brandão and Rio (2003); Ermilov et al (1990); Varandas and Voronin (1995).…”

Section: Empirical Rules For Overtone Intensities Of Stretching Vmentioning

confidence: 97%

“…Absorbance A mn in km/mol and emission intensity I mn in s −1 (Einstein A coefficient) are given by [see, for example, Atkins (1983); Kjaergaard et al (1997); Takahashi et al (2002)],…”

Section: Empirical Rules For Overtone Intensities Of Stretching Vmentioning

confidence: 99%

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Towards understanding the nature of the intensities of overtone vibrational transitions

Medvedev

2012

The Journal of Chemical Physics

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The overtone vibrational transitions, i.e., transitions between states separated by more than one vibrational quantum play important role in many fields of physics and chemistry. The overtone transition is a purely quantum process associated with the so-called dynamical tunneling [Heller, E. J., "The many faces of tunneling," J. Phys. Chem. A 103(49), 10433-10444 (1999)] whose probability is small as compared to the fundamental transition. The transition probability is proportional to the Landau-Lifshitz tunneling factor similar to the Gamov factor in nuclear physics. However, as opposed to the Gamov tunneling, the Landau-Lifshitz tunneling lacks any barrier to tunnel through: Its probability looks as if the system were forced to "dive" under the barrier up to a point where the transition can be performed without any change in momentum, hence with a high probability, and then to "emerge back" in a new state. It follows that the transition probability is associated with the shape of the potential in the classically forbidden region in the same sense as the transition energy is associated with the shape of the potential in the classically allowed region, as implied by the Bohr-Sommerfeld quantization rule, and in the same sense as the probability of the Gamov tunneling is associated with the shape of the potential within the barrier region. As soon as the tunneling character of the transition is recognized, the well-known extreme sensitivity of the overtone intensities to small variations of the fitting function representing the molecular potential [Lehmann, K. K. and Smith, A. M., "Where does overtone intensity come from?" J. Chem. Phys. 93(9), 6140-6147 (1990)] becomes fully understood: Small variations of the potential in the classical region, which do not affect the energy levels significantly, cause large variations in the forbidden region and hence do affect the tunneling factor. This dictates a clear strategy of constructing the potential energy and dipole moment functions (PEF and DMF) capable of explaining the data of vibrational spectroscopy and possessing a predictive power. In this paper, we will show that, for stretching vibrations, knowledge of the inner wall of the PEF is necessary to perform this task. Incorrect behavior of the PEF at extremely small interatomic separations corresponding to energies well above the dissociation limit results in an incorrect rate of the intensity falloff, hence a rapid increase of discrepancies between the calculated and observed intensities with overtone number. Analysis of experimental data on some di- and polyatomic molecules and their interpretations is presented, which shows that neglecting the tunneling nature of overtone transitions does not permit making predictions of the intensities with a known uncertainty. A new approach has to be developed. First of all, an ab initio PEF giving correct energy levels and having correct behavior of the repulsive wall must be constructed; thereafter, an ab initio DMF is invoked to explain the experimental data for lower (obs...

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Section: Introductionsupporting

confidence: 83%

Section: Empirical Rules For Overtone Intensities Of Stretching Vmentioning

confidence: 97%

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Towards understanding the nature of the intensities of overtone vibrational transitions

Medvedev

2012

The Journal of Chemical Physics

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“…The exception is a few molecules that contain a triple bond to which the CH bond is attached. 16 Calculated fundamental intensities were found to improve with the addition of electron correlation. Dipole moment functions calculated with density functional theory (DFT) produce improved fundamental intensities compared to those obtained with the Hartree-Fock (HF) method.…”

Section: Introductionmentioning

confidence: 98%

Absolute Intensities of CH Stretching Overtones in Alkenes

Rong

Henry²,

Robinson³

et al. 2005

J. Phys. Chem. A

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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.

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“…32,33 Vibrational band intensity calculations similar to those reported here have been performed by Kjaergaard, Henry, and others on several molecules using a local mode harmonically coupled anharmonic oscillator model 34 -36 and coupled Morse oscillators. 37 For calculation of the OH fundamental and overtone in HOONO described here, we consider only the OH normal mode.…”

Section: Calculated Transition Strengths Of Cis-cis and Trans-perpmentioning

confidence: 99%

Cis-cis and trans-perp HOONO: Action spectroscopy and isomerization kinetics

Fry

Nizkorodov

Okumura

et al. 2004

The Journal of Chemical Physics

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The weakly bound HOONO product of the OHϩNO 2 ϩM reaction is studied using the vibrational predissociation that follows excitation of the first OH overtone (2 1 ). We observe formation of both cis-cis and trans-perp conformers of HOONO. The trans-perp HOONO 2 1 band is observed under thermal ͑223-238 K͒ conditions at 6971 cm Ϫ1 . We assign the previously published ͑warmer temperature͒ HOONO spectrum to the 2 1 band at 6365 cm Ϫ1 and 2 1 -containing combination bands of the cis-cis conformer of HOONO. The band shape of the trans-perp HOONO spectrum is in excellent agreement with the predicted rotational contour based on previous experimental and theoretical results, but the apparent origin of the cis-cis HOONO spectrum at 6365 cm Ϫ1 is featureless and significantly broader, suggesting more rapid intramolecular vibrational redistribution or predissociation in the latter isomer. The thermally less stable trans-perp HOONO isomerizes rapidly to cis-cis HOONO with an experimentally determined lifetime of 39 ms at 233 K at 13 hPa ͑in a buffer gas of predominantly Ar͒. The temperature dependence of the trans-perp HOONO lifetime in the range 223-238 K yields an isomerization barrier of 33Ϯ12 kJ/mol. New ab initio calculations of the structure and vibrational mode frequencies of the transition state perp-perp HOONO are performed using the coupled cluster singles and doubles with perturbative triples ͓CCSD͑T͔͒ model, using a correlation consistent polarized triple basis set ͑cc-pVTZ͒. The energetics of cis-cis, trans-perp, and perp-perp HOONO are also calculated at this level ͓CCSD͑T͒/ cc-pVTZ͔ and with a quadruple basis set using the structure determined at the triple basis set ͓CCSD͑T͒/cc-pVQZ//CCSD͑T͒/cc-pVTZ͔. These calculations predict that the anti form of perp-perp HOONO has an energy of ⌬E 0 ϭ42.4 kJ/mol above trans-perp HOONO, corresponding to an activation enthalpy of ⌬H 298 ‡0 ϭ41.1 kJ/mol. These results are in good agreement with statistical simulations based on a model developed by Golden, Barker, and Lohr. The simulated isomerization rates match the observed decay rates when modeled with a trans-perp to cis-cis HOONO isomerization barrier of 40.8 kJ/mol and a strong collision model. The quantum yield of cis-cis HOONO dissociation to OH and NO 2 is also calculated as a function of photon excitation energy in the range 3500-7500 cm Ϫ1 , assuming D 0 ϭ83 kJ/mol. The quantum yield is predicted to vary from 0.15 to 1 over the observed spectrum at 298 K, leading to band intensities in the action spectrum that are highly temperature dependent; however, the observed relative band strengths in the cis-cis HOONO spectrum do not change substantially with temperature over the range 193-273 K. Semiempirical calculations of the oscillator strengths for 2 1 (cis-cis HOONO) and 2 1 (trans-perp HOONO) are performed using ͑1͒ a one-dimensional anharmonic model and ͑2͒ a Morse oscillator model for the OH stretch, and ab initio dipole moment functions calculated using Becke, Lee, Yang, and Parr density functional theory ͑B3LYP͒,...

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The role of electron correlation on calculated XH-stretching vibrational band intensities

Cited by 29 publications

References 45 publications

Towards understanding the nature of the intensities of overtone vibrational transitions

Towards understanding the nature of the intensities of overtone vibrational transitions

Absolute Intensities of CH Stretching Overtones in Alkenes

Cis-cis and trans-perp HOONO: Action spectroscopy and isomerization kinetics

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