Energy states and energy flow near the transition states of unimolecular reactions

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The use of lasers with jet-cooled samples has improved energy and angular momentum resolution for the reactant and time resolution for the rate constant by orders of magnitude. The resolution of product quantum states has added a new dimension to unimolecular dynamics. In the past, the geometry, barrier height and vibrational frequencies of the transition state in RRKM theory were adjusted to fit thermal unimolecular reaction rate data. There have been successful quantitative tests of the ability of ab initio theory to calculate transition state geometries accurately and barrier heights to a few kJ/mol for simple molecules. Predicted frequencies tend ... continued below

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19 p.

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Moore, C.B. October 1, 1994.

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  • Moore, C.B. Univ. of California, Berkeley, CA (United States). Dept. of Chemistry

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Description

The use of lasers with jet-cooled samples has improved energy and angular momentum resolution for the reactant and time resolution for the rate constant by orders of magnitude. The resolution of product quantum states has added a new dimension to unimolecular dynamics. In the past, the geometry, barrier height and vibrational frequencies of the transition state in RRKM theory were adjusted to fit thermal unimolecular reaction rate data. There have been successful quantitative tests of the ability of ab initio theory to calculate transition state geometries accurately and barrier heights to a few kJ/mol for simple molecules. Predicted frequencies tend to be somewhat too high for the softest modes which are of most importance in determining rates; however, the basic normal modes and sequence of frequencies seem to be correctly predicted. RRKM theory can be used with ab initio results to predict rate constants to within a factor of two or three and may be used for quantitative extrapolation to conditions not accessible in the laboratory but important in practical situations. Experiments on single molecular eigenstates have revealed quantum statistical fluctuations in rates which are predicted quantitatively in the appropriate extension of RRKM theory. Many experiments seeking to demonstrate non-statistical or non-RRKM dynamics have demonstrated the very wide range of applicability of the RRKM model. A few such experiments have demonstrated a lack of complete vibrational energy randomization in a reactant molecule. Dynamical theory has provided an exact quantum analog to RRKM theory which will combine with future experiments to define the extent to which quantized motion along the reaction coordinate and coupling between the reaction coordinate and vibrational degrees of freedom at the transition state are important. 42 refs., 11 figs.

Physical Description

19 p.

Notes

OSTI as DE95012385

Source

  • 38. conference on chemical research, chemical dynamics of transient species, Houston, TX (United States), 24-25 Oct 1994

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  • Other: DE95012385
  • Report No.: LBL--36640
  • Report No.: CONF-9410349--1
  • Grant Number: AC03-76SF00098
  • DOI: 10.2172/72893 | External Link
  • Office of Scientific & Technical Information Report Number: 72893
  • Archival Resource Key: ark:/67531/metadc706762

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Office of Scientific & Technical Information Technical Reports

Reports, articles and other documents harvested from the Office of Scientific and Technical Information.

Office of Scientific and Technical Information (OSTI) is the Department of Energy (DOE) office that collects, preserves, and disseminates DOE-sponsored research and development (R&D) results that are the outcomes of R&D projects or other funded activities at DOE labs and facilities nationwide and grantees at universities and other institutions.

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  • October 1, 1994

Added to The UNT Digital Library

  • Sept. 12, 2015, 6:31 a.m.

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  • Aug. 23, 2016, 3:02 p.m.

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Moore, C.B. Energy states and energy flow near the transition states of unimolecular reactions, report, October 1, 1994; California. (digital.library.unt.edu/ark:/67531/metadc706762/: accessed December 14, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.