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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.

Abstract：

: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 approximately 3,330 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 normal-mode 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 three-state 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 approximately 25 ps and is 50 times slower than the microcanonical isomerization rate predicted by the statistical Rice-Ramsperger-Kassel-Marcus theory.

journal_name

Proc Natl Acad Sci U S A

journal_title

Proceedings of the National Academy of Sciences of the United States of America

authors

Dian BC,Brown GG,Douglass KO,Rees FS,Johns JE,Nair P,Suenram RD,Pate BH

doi

10.1073/pnas.0800520105

subject

Has Abstract

pub_date

2008-09-02 00:00:00

pages

12696-700

issue

eissn

0027-8424

issn

1091-6490

pii

0800520105

journal_volume

105

pub_type

杂志文章

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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.