{"id":{"repo_id":"mit","oai_identifier":"oai:dspace.mit.edu:1721.1/113971"},"canonical_url":"https://search.dev.ndltd.org/etd/mit/oai:dspace.mit.edu:1721.1/113971","repository":{"repo_id":"mit","name":"MIT","base_url":"https://dspace.mit.edu/oai/request"},"display":{"title":"Exploring the effect of a potential barrier on the molecular rotation-vibration structure","abstract":"The goal of this thesis is to explore the effect of a potential barrier on the rotation-vibration structure of the sulfur dioxide (SO₂) C̃̃ state and the acetylene (HCCH) Ã state. The minimum-energy geometry of both electronically excited states is qualitatively different from their respective electronic ground state geometry. The SO₂ C state exhibits a barrier (~100 cm-¹) at the C₂u, geometry along the antisymmetric-stretching direction, separating two equivalent minimum-energy configurations with C, geometry. The HCCH A-state potential energy surface (PES) supports both trans- and cis-bent conformers (but not a linear configuration). The trans- and cis-conformer-wells are separated by a barrier of ~5000 cm-¹ (above the trans-bent minimum energy). For both the SO₂ C̃ state and the HCCH Ã-state, the presence of a potential barrier greatly complicates the rotation-vibration structure of the molecule. Interpretation of these barrier-related spectroscopic patterns requires both new experimental observations and new analysis tools, both of which are discussed in this thesis. For the SO₂ C̃ state, an IR-UV double-resonance excitation scheme enables direct observations of levels with odd quanta in the antisymmetric-stretching vibrational mode (v3). A new anharmonic force field is derived for the SO₂ C̃ state, which allows accurate determination of the shape of the barrier on the C̃-state PES. In addition, we develop tools, based on perturbation theory, the polyad model, and semiclassical analysis, to interpret the effect of the barrier on the C̃-state rotation-vibration structure. The cis-trans isomerization in the HCCH Ã-state has been the focus of the Field group acetylene project for the past ten years. However, the diminishing detection efficiency of the laser-induced fluorescence (LIF) scheme (due to acetylene predissociation), combined with a partial breakdown of the polyad fit model, has made it increasingly difficult to understand the HCCH A-state level-structure near the top of the cis-trans isomerization barrier. Two new sensitive and convenient action schemes are reported in this thesis to detect predissociated Ã-state rovibrational levels. The first scheme is based on detection of H-atoms by two-photon laser-induced (3d <-- 1s) fluorescence (3d --> 2p), and the second scheme is based on fluorescence detection of C₂ and C₂H fragments, photolyzed via resonance with the probed Ã-state levels. The photodissciation processes that give rise to the strong photofragment fluorescence signals are also studied in this thesis.","abstract_html":"The goal of this thesis is to explore the effect of a potential barrier on the rotation-vibration structure of the sulfur dioxide (SO₂) C̃̃ state and the acetylene (HCCH) Ã state. The minimum-energy geometry of both electronically excited states is qualitatively different from their respective electronic ground state geometry. The SO₂ C state exhibits a barrier (~100 cm-¹) at the C₂u, geometry along the antisymmetric-stretching direction, separating two equivalent minimum-energy configurations with C, geometry. The HCCH A-state potential energy surface (PES) supports both trans- and cis-bent conformers (but not a linear configuration). The trans- and cis-conformer-wells are separated by a barrier of ~5000 cm-¹ (above the trans-bent minimum energy). For both the SO₂ C̃ state and the HCCH Ã-state, the presence of a potential barrier greatly complicates the rotation-vibration structure of the molecule. Interpretation of these barrier-related spectroscopic patterns requires both new experimental observations and new analysis tools, both of which are discussed in this thesis. For the SO₂ C̃ state, an IR-UV double-resonance excitation scheme enables direct observations of levels with odd quanta in the antisymmetric-stretching vibrational mode (v3). A new anharmonic force field is derived for the SO₂ C̃ state, which allows accurate determination of the shape of the barrier on the C̃-state PES. In addition, we develop tools, based on perturbation theory, the polyad model, and semiclassical analysis, to interpret the effect of the barrier on the C̃-state rotation-vibration structure. The cis-trans isomerization in the HCCH Ã-state has been the focus of the Field group acetylene project for the past ten years. However, the diminishing detection efficiency of the laser-induced fluorescence (LIF) scheme (due to acetylene predissociation), combined with a partial breakdown of the polyad fit model, has made it increasingly difficult to understand the HCCH A-state level-structure near the top of the cis-trans isomerization barrier. Two new sensitive and convenient action schemes are reported in this thesis to detect predissociated Ã-state rovibrational levels. The first scheme is based on detection of H-atoms by two-photon laser-induced (3d &lt;-- 1s) fluorescence (3d --&gt; 2p), and the second scheme is based on fluorescence detection of C₂ and C₂H fragments, photolyzed via resonance with the probed Ã-state levels. The photodissciation processes that give rise to the strong photofragment fluorescence signals are also studied in this thesis.","abstract_has_math":false,"creators":["Jiang, Jun, Ph. D. Massachusetts Institute of Technology"],"institution":"Massachusetts Institute of Technology","degree_name":null,"degree_level":null,"degree_discipline":null,"degree_department":"Massachusetts Institute of Technology. Department of Chemistry.","school":null,"contributors":[],"advisors":["Robert W. Field."],"committee_chairs":[],"committee_members":[],"year":2017,"date_issued":"2017","date_published":"2017","updated_at":"2026-07-22T22:22:20Z","subjects":["Chemistry."],"languages":["eng"],"rights":["MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission."],"rights_urls":["http://dspace.mit.edu/handle/1721.1/7582"],"identifier_entries":[]},"links":{"outbound_url":"http://hdl.handle.net/1721.1/113971","outbound_label":"Handle","outbound_source":"dc:identifier.uri"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor.advisor","label":"Advisor","values":["Robert W. Field."]},{"key":"dc:contributor.department","label":"Department","values":["Massachusetts Institute of Technology. Department of Chemistry."]},{"key":"dc:contributor.other","label":"Dc Contributor Other","values":["Massachusetts Institute of Technology. Department of Chemistry."]},{"key":"dc:creator","label":"Author","values":["Jiang, Jun, Ph. D. Massachusetts Institute of Technology"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.accessioned","label":"Dc Date Accessioned","values":["2018-03-02T22:21:10Z"]},{"key":"dc:date.available","label":"Dc Date Available","values":["2018-03-02T22:21:10Z"]},{"key":"dc:date.issued","label":"Date","values":["2017"]},{"key":"dc:publisher","label":"Institution","values":["Massachusetts Institute of Technology"]},{"key":"dc:type","label":"Dc Type","values":["Thesis"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Chemistry."]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language.iso","label":"Language (ISO)","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission."]},{"key":"dc:rights.uri","label":"Rights URI","values":["http://dspace.mit.edu/handle/1721.1/7582"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier.uri","label":"Identifier URI","values":["http://hdl.handle.net/1721.1/113971"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017.","Cataloged from PDF version of thesis.","Includes bibliographical references (pages 265-279)."]},{"key":"dc:description.abstract","label":"Abstract","values":["The goal of this thesis is to explore the effect of a potential barrier on the rotation-vibration structure of the sulfur dioxide (SO₂) C̃̃ state and the acetylene (HCCH) Ã state. The minimum-energy geometry of both electronically excited states is qualitatively different from their respective electronic ground state geometry. The SO₂ C state exhibits a barrier (~100 cm-¹) at the C₂u, geometry along the antisymmetric-stretching direction, separating two equivalent minimum-energy configurations with C, geometry. The HCCH A-state potential energy surface (PES) supports both trans- and cis-bent conformers (but not a linear configuration). The trans- and cis-conformer-wells are separated by a barrier of ~5000 cm-¹ (above the trans-bent minimum energy). For both the SO₂ C̃ state and the HCCH Ã-state, the presence of a potential barrier greatly complicates the rotation-vibration structure of the molecule. Interpretation of these barrier-related spectroscopic patterns requires both new experimental observations and new analysis tools, both of which are discussed in this thesis. For the SO₂ C̃ state, an IR-UV double-resonance excitation scheme enables direct observations of levels with odd quanta in the antisymmetric-stretching vibrational mode (v3). A new anharmonic force field is derived for the SO₂ C̃ state, which allows accurate determination of the shape of the barrier on the C̃-state PES. In addition, we develop tools, based on perturbation theory, the polyad model, and semiclassical analysis, to interpret the effect of the barrier on the C̃-state rotation-vibration structure. The cis-trans isomerization in the HCCH Ã-state has been the focus of the Field group acetylene project for the past ten years. However, the diminishing detection efficiency of the laser-induced fluorescence (LIF) scheme (due to acetylene predissociation), combined with a partial breakdown of the polyad fit model, has made it increasingly difficult to understand the HCCH A-state level-structure near the top of the cis-trans isomerization barrier. Two new sensitive and convenient action schemes are reported in this thesis to detect predissociated Ã-state rovibrational levels. The first scheme is based on detection of H-atoms by two-photon laser-induced (3d <-- 1s) fluorescence (3d --> 2p), and the second scheme is based on fluorescence detection of C₂ and C₂H fragments, photolyzed via resonance with the probed Ã-state levels. The photodissciation processes that give rise to the strong photofragment fluorescence signals are also studied in this thesis."]},{"key":"dc:description.degree","label":"Dc Description Degree","values":["Ph. D."]},{"key":"dc:title","label":"Title","values":["Exploring the effect of a potential barrier on the molecular rotation-vibration structure"]}]}],"canonical_facts":{"dc:contributor.advisor":["Robert W. Field."],"dc:contributor.department":["Massachusetts Institute of Technology. Department of Chemistry."],"dc:contributor.other":["Massachusetts Institute of Technology. Department of Chemistry."],"dc:creator":["Jiang, Jun, Ph. D. Massachusetts Institute of Technology"],"dc:date.accessioned":["2018-03-02T22:21:10Z"],"dc:date.available":["2018-03-02T22:21:10Z"],"dc:date.issued":["2017"],"dc:description":["Thesis: Ph. D., Massachusetts Institute of Technology, Department of Chemistry, 2017.","Cataloged from PDF version of thesis.","Includes bibliographical references (pages 265-279)."],"dc:description.abstract":["The goal of this thesis is to explore the effect of a potential barrier on the rotation-vibration structure of the sulfur dioxide (SO₂) C̃̃ state and the acetylene (HCCH) Ã state. The minimum-energy geometry of both electronically excited states is qualitatively different from their respective electronic ground state geometry. The SO₂ C state exhibits a barrier (~100 cm-¹) at the C₂u, geometry along the antisymmetric-stretching direction, separating two equivalent minimum-energy configurations with C, geometry. The HCCH A-state potential energy surface (PES) supports both trans- and cis-bent conformers (but not a linear configuration). The trans- and cis-conformer-wells are separated by a barrier of ~5000 cm-¹ (above the trans-bent minimum energy). For both the SO₂ C̃ state and the HCCH Ã-state, the presence of a potential barrier greatly complicates the rotation-vibration structure of the molecule. Interpretation of these barrier-related spectroscopic patterns requires both new experimental observations and new analysis tools, both of which are discussed in this thesis. For the SO₂ C̃ state, an IR-UV double-resonance excitation scheme enables direct observations of levels with odd quanta in the antisymmetric-stretching vibrational mode (v3). A new anharmonic force field is derived for the SO₂ C̃ state, which allows accurate determination of the shape of the barrier on the C̃-state PES. In addition, we develop tools, based on perturbation theory, the polyad model, and semiclassical analysis, to interpret the effect of the barrier on the C̃-state rotation-vibration structure. The cis-trans isomerization in the HCCH Ã-state has been the focus of the Field group acetylene project for the past ten years. However, the diminishing detection efficiency of the laser-induced fluorescence (LIF) scheme (due to acetylene predissociation), combined with a partial breakdown of the polyad fit model, has made it increasingly difficult to understand the HCCH A-state level-structure near the top of the cis-trans isomerization barrier. Two new sensitive and convenient action schemes are reported in this thesis to detect predissociated Ã-state rovibrational levels. The first scheme is based on detection of H-atoms by two-photon laser-induced (3d <-- 1s) fluorescence (3d --> 2p), and the second scheme is based on fluorescence detection of C₂ and C₂H fragments, photolyzed via resonance with the probed Ã-state levels. The photodissciation processes that give rise to the strong photofragment fluorescence signals are also studied in this thesis."],"dc:description.degree":["Ph. D."],"dc:identifier.uri":["http://hdl.handle.net/1721.1/113971"],"dc:language.iso":["eng"],"dc:publisher":["Massachusetts Institute of Technology"],"dc:rights":["MIT theses are protected by copyright. They may be viewed, downloaded, or printed from this source but further reproduction or distribution in any format is prohibited without written permission."],"dc:rights.uri":["http://dspace.mit.edu/handle/1721.1/7582"],"dc:subject":["Chemistry."],"dc:title":["Exploring the effect of a potential barrier on the molecular rotation-vibration structure"],"dc:type":["Thesis"]},"updated_at":"2026-07-22T22:22:20Z"}