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High-resolution infrared spectroscop...

Whitney, Erin Sue.

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High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system.

Record Type:	Language materials, printed : Monograph/item
Title/Author:	High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system./
Author:	Whitney, Erin Sue.
Description:	173 p.
Notes:	Adviser: David J. Nesbitt.
Contained By:	Dissertation Abstracts International67-02B.
Subject:	Chemistry, Physical. -
Online resource:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3207681
ISBN:	9780542552304

High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system.
Whitney, Erin Sue.

High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system. - 173 p.

Adviser: David J. Nesbitt.

Thesis (Ph.D.)--University of Colorado at Boulder, 2006.

This thesis describes a series of projects whose common theme comprises the structure and internal energy distribution of gas-phase radicals. In the first two projects, shot noise-limited direct absorption spectroscopy is combined with long path-length slit supersonic discharges to obtain first high-resolution infrared spectra for jet-cooled CH2F and CH2Cl in the symmetric and antisymmetric CH2 stretching modes. Drawing motivation from the question of the equilibrium structures of halogen-substituted methyl radicals, spectral assignment yields refined lower and upper state rotational constants, as well as fine-structure parameters from least-square fits to the sub-Doppler lineshapes for individual transitions. High-level CCSD(T) calculations extrapolated to the complete basis set (CBS) limit confirm the existence of a non-planar (theta=29°) CH2F equilibrium structure with a 132 cm-1 barrier to planarity and a vibrational bend frequency of 276 cm-1. Similar calculations for CH 2Cl predict a slightly nonplanar equilibrium structure (theta=11°) with a vibrationally adiabatic one-dimensional treatment of the bend coordinate yielding a fundamental anharmonic frequency (393 cm-1). Both sets of calculations are in excellent agreement with previous studies.

ISBN: 9780542552304Subjects--Topical Terms:

560527
Chemistry, Physical.

High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system.
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020 $a 9780542552304
035 $a (UMI)AAI3207681
035 $a AAI3207681
040 $a UMI $c UMI
100 1 $a Whitney, Erin Sue. $3 1291368
245 1 0 $a High-resolution infrared spectroscopy: Jet-cooled halogenated methyl radicals and reactive scattering dynamics in an atom + polyatom system.
300 $a 173 p.
500 $a Adviser: David J. Nesbitt.
500 $a Source: Dissertation Abstracts International, Volume: 67-02, Section: B, page: 0914.
502 $a Thesis (Ph.D.)--University of Colorado at Boulder, 2006.
520 $a This thesis describes a series of projects whose common theme comprises the structure and internal energy distribution of gas-phase radicals. In the first two projects, shot noise-limited direct absorption spectroscopy is combined with long path-length slit supersonic discharges to obtain first high-resolution infrared spectra for jet-cooled CH2F and CH2Cl in the symmetric and antisymmetric CH2 stretching modes. Drawing motivation from the question of the equilibrium structures of halogen-substituted methyl radicals, spectral assignment yields refined lower and upper state rotational constants, as well as fine-structure parameters from least-square fits to the sub-Doppler lineshapes for individual transitions. High-level CCSD(T) calculations extrapolated to the complete basis set (CBS) limit confirm the existence of a non-planar (theta=29°) CH2F equilibrium structure with a 132 cm-1 barrier to planarity and a vibrational bend frequency of 276 cm-1. Similar calculations for CH 2Cl predict a slightly nonplanar equilibrium structure (theta=11°) with a vibrationally adiabatic one-dimensional treatment of the bend coordinate yielding a fundamental anharmonic frequency (393 cm-1). Both sets of calculations are in excellent agreement with previous studies.
520 $a More interesting, however, are the unexpected intensity ratios of the symmetric vs. antisymmetric bands for CH2F and the absence of an antisymmetric band for CH2Cl. While a simple bond-dipole picture predicts a ratio of 1:3 for the symmetric vs. antisymmetric intensities, the experimentally observed value for CH2F is &sim;2:1. This ratio is confirmed by DFT [B3LYP/aug-cc-pVTZ] calculations in a novel albeit indirect probe of the effective non-planarity for CH2F. For CH2Cl, similar DFT calculations predict a 30-fold decrease between the intensity of the symmetric and antisymmetric CH2 stretches, leading to the postulation of a nearly perfect cancellation of antisymmetric stretch intensity transition moment with chlorination.
520 $a These two projects are followed by an investigation utilizing a well-characterized radical source, F, in a reaction with ethane to form HF and ethyl radical. The non-radical HF product is detected directly through similar high-resolution infrared absorption methods as described above, and its analysis is used to make inferences about the internal energy redistribution of the other radical fragment, ethyl. State-to-state reaction dynamics under single collision conditions are interpreted in the context of a simple impulsive model based on conservation of linear/angular momentum yields predictions in good agreement with experiment. Deviations from the model indicate only minor excitation of the ethyl vibrations, in contrast with a picture of extensive intramolecular vibrational energy flow but consistent with Franck-Condon excitation of the methylene CH2 bending mode. The results suggest a relatively simple dynamical picture for exothermic atom + polyatomic scattering, i.e., that of early barrier dynamics in atom + diatom systems but modified by impulsive recoil coupling at the transition state between translational/rotational degrees of freedom.
590 $a School code: 0051.
650 4 $a Chemistry, Physical. $3 560527
650 4 $a Physics, Molecular. $3 1018648
690 $a 0494
690 $a 0609
710 2 0 $a University of Colorado at Boulder. $3 1019435
773 0 $t Dissertation Abstracts International $g 67-02B.
790 $a 0051
790 1 0 $a Nesbitt, David J., $e advisor
791 $a Ph.D.
792 $a 2006
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=3207681