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HIGH RESOLUTION ELECTRONIC SPECTROSCOPY OF NITROGEN-CONTAINING MOLECULES IN THE GAS PHASE: 26DAP AND PYRBN

Clements, Casey Lynn (2011) HIGH RESOLUTION ELECTRONIC SPECTROSCOPY OF NITROGEN-CONTAINING MOLECULES IN THE GAS PHASE: 26DAP AND PYRBN. Master's Thesis, University of Pittsburgh.

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    Abstract

    High resolution gas phase electronic spectra were recorded for 2,6-diaminopyridine (26DAP) and pyrrolidinobenzonitrile (PYRBN). A comparison of the electronic properties of the nitrogen-containing rings aniline, 2-aminopyridine, and 2,6-diaminopyridine (26DAP) shows that the potential energy surface of the molecule is significantly affected as more nitrogen atoms are added to the system. High resolution, rotationally resolved spectra of four vibrational bands in the S1 - S0 electronic transition of 26DAP were obtained in order to explain these changes. The zigzagging inertial defects point to a double minimum excited state potential energy surface along the coupled amino group inversion vibrational mode, which becomes a four-fold well (and barrier) problem when the existence of two nearly degenerate isomers is taken into account. Assuming that the molecules are in the lower energy, opposite-side configuration, ab initio calculations were performed using the MP2/6-31G** level of theory to create a potential energy surface modeling the simultaneous antisymmetric NH2-inversion mode. The calculated potential energy surface shows a ground electronic state barrier to simultaneous NH2 inversion of ~ 220 cm-1, and a fit to experimental vibrational energy level spacings and relative intensities produces an excited electronic state barrier of ~ 400 cm-1. The ground state barrier is less than that in aniline, but the excited state barrier is larger.Pyrrolidinobenzonitrile (PYRBN), a derivative of DMABN, has been examined here using high resolution fluorescence excitation spectroscopy in the presence of an electric field varying from 0 - 846 V/cm. The b-type fluorescence band reveals that the transition moment is along the short, in plane axis of the molecule. Upon excitation the inertial defect remains unchanged, which suggests that the molecule's planarity remains constant. The dipole moment is found to increase from 8.06 to 10.45 D upon electronic excitation. This analysis of PYRBN leads to many interesting comparisons to 1PP including their transition moments, dipole moments, and inertial defects.


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    Item Type: University of Pittsburgh ETD
    Creators/Authors:
    CreatorsEmailORCID
    Clements, Casey Lynnclc171@pitt.edu
    ETD Committee:
    ETD Committee TypeCommittee MemberEmailORCID
    Committee ChairPratt, Davidpratt@pitt.edu
    Committee MemberWaldeck, Daviddave@pitt.edu
    Committee MemberChong, Lillianltchong@pitt.edu
    Title: HIGH RESOLUTION ELECTRONIC SPECTROSCOPY OF NITROGEN-CONTAINING MOLECULES IN THE GAS PHASE: 26DAP AND PYRBN
    Status: Unpublished
    Abstract: High resolution gas phase electronic spectra were recorded for 2,6-diaminopyridine (26DAP) and pyrrolidinobenzonitrile (PYRBN). A comparison of the electronic properties of the nitrogen-containing rings aniline, 2-aminopyridine, and 2,6-diaminopyridine (26DAP) shows that the potential energy surface of the molecule is significantly affected as more nitrogen atoms are added to the system. High resolution, rotationally resolved spectra of four vibrational bands in the S1 - S0 electronic transition of 26DAP were obtained in order to explain these changes. The zigzagging inertial defects point to a double minimum excited state potential energy surface along the coupled amino group inversion vibrational mode, which becomes a four-fold well (and barrier) problem when the existence of two nearly degenerate isomers is taken into account. Assuming that the molecules are in the lower energy, opposite-side configuration, ab initio calculations were performed using the MP2/6-31G** level of theory to create a potential energy surface modeling the simultaneous antisymmetric NH2-inversion mode. The calculated potential energy surface shows a ground electronic state barrier to simultaneous NH2 inversion of ~ 220 cm-1, and a fit to experimental vibrational energy level spacings and relative intensities produces an excited electronic state barrier of ~ 400 cm-1. The ground state barrier is less than that in aniline, but the excited state barrier is larger.Pyrrolidinobenzonitrile (PYRBN), a derivative of DMABN, has been examined here using high resolution fluorescence excitation spectroscopy in the presence of an electric field varying from 0 - 846 V/cm. The b-type fluorescence band reveals that the transition moment is along the short, in plane axis of the molecule. Upon excitation the inertial defect remains unchanged, which suggests that the molecule's planarity remains constant. The dipole moment is found to increase from 8.06 to 10.45 D upon electronic excitation. This analysis of PYRBN leads to many interesting comparisons to 1PP including their transition moments, dipole moments, and inertial defects.
    Date: 27 January 2011
    Date Type: Completion
    Defense Date: 19 November 2010
    Approval Date: 27 January 2011
    Submission Date: 19 November 2010
    Access Restriction: No restriction; The work is available for access worldwide immediately.
    Patent pending: No
    Institution: University of Pittsburgh
    Thesis Type: Master's Thesis
    Refereed: Yes
    Degree: MS - Master of Science
    URN: etd-11192010-104810
    Uncontrolled Keywords: double minimum
    Schools and Programs: Dietrich School of Arts and Sciences > Chemistry
    Date Deposited: 10 Nov 2011 15:05
    Last Modified: 14 May 2012 11:02
    Other ID: http://etd.library.pitt.edu/ETD/available/etd-11192010-104810/, etd-11192010-104810

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