The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe
<p>This thesis presents an experimental and theoretical study of the collision dynamics of OH(A<sup>2</sup>Σ<sup>+</sup>) with Kr and Xe. These two systems both exhibit a significant degree of electronically non-adiabatic behaviour, and a particular emphasis of the work...
| Main Authors: | , |
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| Other Authors: | |
| Format: | Thesis |
| Language: | English |
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2014
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| _version_ | 1797070162089738240 |
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| author | Perkins, T Thomas Perkins |
| author2 | Brouard, M |
| author_facet | Brouard, M Perkins, T Thomas Perkins |
| author_sort | Perkins, T |
| collection | OXFORD |
| description | <p>This thesis presents an experimental and theoretical study of the collision dynamics of OH(A<sup>2</sup>Σ<sup>+</sup>) with Kr and Xe. These two systems both exhibit a significant degree of electronically non-adiabatic behaviour, and a particular emphasis of the work presented here is to characterise the competition and interplay between electronic quenching on the one hand, and electronically adiabatic collisional processes on the other. Quenching takes place close to the bottom of the deepest potential well for both systems. In collisions that remain in the excited electronic state, this same region of the potential is also largely responsible for rotational energy transfer (RET) and the collisional depolarisation of angular momentum. Therefore, the direct competition between these processes suppresses the cross-sections for RET and collisional depolarisation from their expected value in the absence of quenching.</p> <p>To investigate this, experiments were carried out to measure cross-sections for the collisional transfer of electronic, vibrational and rotational energy in OH(A, <em>v</em>=0,1) + Kr and OH(A, <em>v</em>=0) + Xe. In addition, measurements were made of the <em>j-j'</em> correlation -- that is, the relationship between the angular momentum of the OH radical before and after a collision -- in collisions with Kr and Xe, using the experimental technique of <em>Zeeman quantum beat spectroscopy</em>. Collisions with both Kr and Xe tend to effectively depolarise the angular momentum of the OH radical, due to the very anisotropic character of the potential on which the process occurs. Electronic quenching, which plays an essential role in both systems, is more prevalent with xenon as the crossing to the ground state potential is located in a more accessible location.</p> <p>These experimental results were compared with single surface quasi-classical trajectory (QCT) calculations, where the overestimate of rotational energy transfer or collisional depolarisation helps to elucidate the degree to which the presence of quenching suppresses these processes. Surface hopping QCT was then used to account for non-adiabatic transitions in the theory, which led to an improvement in agreement with experiment. However, standard surface hopping QCT theory failed to account for the full extent of quenching in these two systems.</p> <p>A major focus of this work is therefore on the development of an extension to standard surface hopping QCT theory to incorporate rovibronic couplings. In non-linear configurations, the excited state of the OH + Kr, Xe systems has <em>A'</em> symmetry, while the ground state is split into symmetric (<em>A'</em>) and antisymmetric (<em>A''</em>) components. For these symmetry reasons, coupling is restricted to the two states of the same symmetry, however a rotation of the correct (<em>A''</em>) symmetry can induce transitions to the <em>A''</em> state too. Inclusion of all three electronic states, and the relevant couplings between them, is found to be crucial for a proper description of experimental reality.</p> |
| first_indexed | 2024-03-06T22:35:02Z |
| format | Thesis |
| id | oxford-uuid:5998e249-35ff-4d05-9c13-9b65d59b11d9 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T22:35:02Z |
| publishDate | 2014 |
| record_format | dspace |
| spelling | oxford-uuid:5998e249-35ff-4d05-9c13-9b65d59b11d92022-03-26T17:10:43ZThe effects of electronic quenching on the collision dynamics of OH(A) with Kr and XeThesishttp://purl.org/coar/resource_type/c_db06uuid:5998e249-35ff-4d05-9c13-9b65d59b11d9Photochemistry and reaction dynamicsPhysical & theoretical chemistryTheoretical chemistrySpectroscopy and molecular structureComputational chemistryLaser SpectroscopyAtomic and laser physicsChemical kineticsChemistry & allied sciencesPhysical SciencesEnglishOxford University Research Archive - Valet2014Perkins, TThomas PerkinsBrouard, M<p>This thesis presents an experimental and theoretical study of the collision dynamics of OH(A<sup>2</sup>Σ<sup>+</sup>) with Kr and Xe. These two systems both exhibit a significant degree of electronically non-adiabatic behaviour, and a particular emphasis of the work presented here is to characterise the competition and interplay between electronic quenching on the one hand, and electronically adiabatic collisional processes on the other. Quenching takes place close to the bottom of the deepest potential well for both systems. In collisions that remain in the excited electronic state, this same region of the potential is also largely responsible for rotational energy transfer (RET) and the collisional depolarisation of angular momentum. Therefore, the direct competition between these processes suppresses the cross-sections for RET and collisional depolarisation from their expected value in the absence of quenching.</p> <p>To investigate this, experiments were carried out to measure cross-sections for the collisional transfer of electronic, vibrational and rotational energy in OH(A, <em>v</em>=0,1) + Kr and OH(A, <em>v</em>=0) + Xe. In addition, measurements were made of the <em>j-j'</em> correlation -- that is, the relationship between the angular momentum of the OH radical before and after a collision -- in collisions with Kr and Xe, using the experimental technique of <em>Zeeman quantum beat spectroscopy</em>. Collisions with both Kr and Xe tend to effectively depolarise the angular momentum of the OH radical, due to the very anisotropic character of the potential on which the process occurs. Electronic quenching, which plays an essential role in both systems, is more prevalent with xenon as the crossing to the ground state potential is located in a more accessible location.</p> <p>These experimental results were compared with single surface quasi-classical trajectory (QCT) calculations, where the overestimate of rotational energy transfer or collisional depolarisation helps to elucidate the degree to which the presence of quenching suppresses these processes. Surface hopping QCT was then used to account for non-adiabatic transitions in the theory, which led to an improvement in agreement with experiment. However, standard surface hopping QCT theory failed to account for the full extent of quenching in these two systems.</p> <p>A major focus of this work is therefore on the development of an extension to standard surface hopping QCT theory to incorporate rovibronic couplings. In non-linear configurations, the excited state of the OH + Kr, Xe systems has <em>A'</em> symmetry, while the ground state is split into symmetric (<em>A'</em>) and antisymmetric (<em>A''</em>) components. For these symmetry reasons, coupling is restricted to the two states of the same symmetry, however a rotation of the correct (<em>A''</em>) symmetry can induce transitions to the <em>A''</em> state too. Inclusion of all three electronic states, and the relevant couplings between them, is found to be crucial for a proper description of experimental reality.</p> |
| spellingShingle | Photochemistry and reaction dynamics Physical & theoretical chemistry Theoretical chemistry Spectroscopy and molecular structure Computational chemistry Laser Spectroscopy Atomic and laser physics Chemical kinetics Chemistry & allied sciences Physical Sciences Perkins, T Thomas Perkins The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title | The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title_full | The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title_fullStr | The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title_full_unstemmed | The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title_short | The effects of electronic quenching on the collision dynamics of OH(A) with Kr and Xe |
| title_sort | effects of electronic quenching on the collision dynamics of oh a with kr and xe |
| topic | Photochemistry and reaction dynamics Physical & theoretical chemistry Theoretical chemistry Spectroscopy and molecular structure Computational chemistry Laser Spectroscopy Atomic and laser physics Chemical kinetics Chemistry & allied sciences Physical Sciences |
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