Molecular rotation in the presence of intramolecular vibrational energy redistribution

Keske, John C.; McWhorter, David A.; Pate, Brooks H.

doi:10.1080/01442350050034171

Cited by 53 publications

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“…The timedependent moments of inertia resulting from IVR and isomerization dynamics produce changes in the spectrum that are similar to well known effects in NMR spectroscopy (7,8): motional narrowing is caused by IVR (9, 10) and, as demonstrated here, coalescence of the spectrum is produced by isomerization (11). The analogies between the new features in the rotational spectra of highly excited molecules and the dynamical effects in NMR spectra are the basis for calling this technique ''dynamic rotational spectroscopy'' (12).…”

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confidence: 67%

“…The reaction rate for each conformer into the delocalized torsional levels is varied independently. The contours drawn on the plot give the conformational isomerization time scale that comes from the kinetic model underlying the Bloch analysis (12). The relationship between these rates and the overall isomerization reaction rate are described in more detail in SI Text.…”

Section: Resultsmentioning

confidence: 99%

“…The isomerization rate is obtained from an analysis of the overall rotational line shape by using a three-state microwave spectroscopy Bloch model modified for chemical exchange (12). In this model, the cis and skew structures interact by coupling to above-barrier 1D torsional levels.…”

Section: Resultsmentioning

confidence: 99%

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Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy

Dian

Brown

Douglass

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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We demonstrate the application of molecular rotational spectroscopy to measure the conformation isomerization rate of vibrationally excited pent-1-en-4-yne (pentenyne). The rotational spectra of single quantum states of pentenyne are acquired by using a combination of IR-Fourier transform microwave double-resonance spectroscopy and high-resolution, single-photon IR spectroscopy. The quantum states probed in these experiments have energy eigenvalues of Ϸ3,330 cm ؊1 and lie above the barrier to conformational isomerization. At this energy, the presence of intramolecular vibrational energy redistribution (IVR) is indicated through the extensive local perturbations found in the high-resolution rotation-vibration spectrum of the acetylenic C-H stretch normalmode fundamental. The fact that the IVR process produces isomerization is deduced through a qualitatively different appearance of the excited-state rotational spectra compared with the pure rotational spectra of pentenyne. The rotational spectra of the vibrationally excited molecular eigenstates display coalescence between the characteristic rotational frequencies of the stable cis and skew conformations of the molecule. This coalescence is observed for quantum states prepared from laser excitation originating in the ground vibrational state of either of the two stable conformers. Experimental isomerization rates are extracted by using a threestate Bloch model of the dynamic rotational spectra that includes the effects of chemical exchange between the stable conformations. The time scale for the conformational isomerization rate of pentenyne at total energy of 3,330 cm ؊1 is Ϸ25 ps and is 50 times slower than the microcanonical isomerization rate predicted by the statistical Rice-Ramsperger-Kassel-Marcus theory.IVR ͉ microwave ͉ infrared ͉ double-resonance R otational spectroscopy is one of the most powerful tools in physical chemistry for the determination of gas-phase molecular structure (1). The development of molecular beam spectrometers for rotational spectroscopy-most notably the Fourier-transform microwave (FTMW) spectroscopy technique introduced by Balle and Flygare (2)-has greatly expanded the range of chemical systems that can be studied. Rotational spectroscopy can be routinely used to study challenging structural problems such as the conformations of large molecules (3), weakly bound molecular complexes (4), and radicals (5). In addition, rotational spectroscopy of low-energy vibrational and torsional levels can be used to determine accurate potential energy surfaces for large amplitude motion in ''floppy'' systems (1). Here we demonstrate a fundamentally unique application of rotational spectroscopy. We show that isomerization kinetics can be determined from the rotational spectrum of a highly vibrationally excited molecule.The physical basis of pure rotational spectroscopy is that when the total angular momentum is conserved, the rotational frequency is directly related to the principal moments of inertia of the molecule and, therefore, to its struct...

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confidence: 67%

Section: Resultsmentioning

confidence: 99%

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Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy

Dian

Brown

Douglass

et al. 2008

Proc. Natl. Acad. Sci. U.S.A.

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“…Trapped by a Bottleneck. A second curious instance of inhibition of IVR has been observed in molecules for which acetylene is a prototype 49 with a dramatic decrease in isomerization rate. There is reason to suspect that this too is connected with the ability of the polyad constant to act as a severe constraint on energy flow.…”

Section: Energy Flow and Chemical Reactivitymentioning

confidence: 99%

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

Kellman

Tyng

2007

Acc. Chem. Res.

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At low energies, molecular vibrational motion is described by the normal modes model. This model breaks down at higher energy, with strong coupling between normal modes and onset of chaotic dynamics. New anharmonic modes are born in bifurcations, or branchings of the normal modes. Knowledge of these new modes is obtained through the window of frequency-domain spectroscopy, using techniques of nonlinear classical dynamics. It may soon be possible to "watch" molecular rearrangement reactions spectroscopically. Connections are being made with reaction rate theories, condensed phase systems, and motions of electrons in quantum dots.

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“…The involvement of rotations, torsions, and other large amplitude modes in molecular systems and their implications for IVR [210] and dynamical tunneling have received relatively less attention. Early pioneering studies [4] by Harter and Patterson showed that the splitting of the doubly degenerate Klevels of a symmetric top on the introduction of asymmetry could be associated with tunneling across a separatrix on the so called rotational energy surface.…”

Section: Local Mode Doubletsmentioning

confidence: 99%

Dynamical tunnelling in molecules: quantum routes to energy flow

Keshavamurthy¹

2007

International Reviews in Physical Chemistry

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Dynamical tunneling, introduced in the molecular context, is more than two decades old and refers to phenomena that are classically forbidden but allowed by quantum mechanics. The barriers for dynamical tunneling, however, can arise in the momentum or more generally in the full phase space of the system. On the other hand the phenomenon of intramolecular vibrational energy redistribution (IVR) has occupied a central place in the field of chemical physics for a much longer period of time. Despite significant progress in understanding IVR a priori prediction of the pathways and rates is still a difficult task. Although the two phenomena seem to be unrelated several studies indicate that dynamical tunneling, in terms of its mechanism and timescales, can have important implications for IVR. It is natural to associate dynamical tunneling with a purely quantum mechanism of IVR. Examples include the observation of local mode doublets, clustering of rotational energy levels, and extremely narrow vibrational features in high resolution molecular spectra. Many researchers have demonstrated the usefulness of a phase space perspective towards understanding the mechanism of IVR. Interestingly dynamical tunneling is also strongly influenced by the nature of the underlying classical phase space. Recent studies show that chaos and nonlinear resonances in the phase space can enhance or suppress dynamical tunneling by many orders of magnitude. Is it then possible that both the classical and quantum mechanisms of IVR, and the potential competition between them, can be understood within the phase space perspective? This review focuses on addressing the question by providing the current state of understanding of dynamical tunneling from the phase space perspective and the consequences for intramolecular vibrational energy flow in polyatomic molecules.

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Molecular rotation in the presence of intramolecular vibrational energy redistribution

Cited by 53 publications

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Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy

Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

Dynamical tunnelling in molecules: quantum routes to energy flow

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Molecular rotation in the presence of intramolecular vibrational energy redistribution

Cited by 53 publications

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Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm −1 of internal energy measured by dynamic rotational spectroscopy

Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm −1 of internal energy measured by dynamic rotational spectroscopy

The Dance of Molecules: New Dynamical Perspectives on Highly Excited Molecular Vibrations

Dynamical tunnelling in molecules: quantum routes to energy flow

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Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy

Conformational isomerization kinetics of pent-1-en-4-yne with 3,330 cm ⁻¹ of internal energy measured by dynamic rotational spectroscopy