Theoretical chemistry has advanced to the point where spectroscopic data can be produced that is directly comparable to high-accuracy experimental results. Quartic force field (QFFs) methods are one of the most efficient means of generating this data and have even shown spectroscopic accuracy (±1 cm−1) for fundamental vibrational frequencies. A method for extending QFFs to variationally inaccessible electronically excited states is presented herein using equation-of-motion (EOM) coupled cluster theory. The new EOM-based QFF is tested against the traditional QFF method using the isoformyl (HOC) radical’s variationally accessible 1 A” excited state and compared to previous benchmark studies. Challenges presented in this study are addressed in a second paper exploring the ethynyl (C2H) radical’s ground X 2Σ+ state and low-lying A 2Π state as well as its anionic form, the acetylide anion (C2H−). Special basis sets designed to treat diffuse (dipole-bound) states are developed in the final chapter which lays the foundation for the treatment of larger systems, such as anions, that posses dipole-bound excited states.
","abstract_html":"<p>Theoretical chemistry has advanced to the point where spectroscopic data can be produced that is directly comparable to high-accuracy experimental results. Quartic force field (QFFs) methods are one of the most efficient means of generating this data and have even shown spectroscopic accuracy (±1 cm−1) for fundamental vibrational frequencies. A method for extending QFFs to variationally inaccessible electronically excited states is presented herein using equation-of-motion (EOM) coupled cluster theory. The new EOM-based QFF is tested against the traditional QFF method using the isoformyl (HOC) radical’s variationally accessible 1 A” excited state and compared to previous benchmark studies. Challenges presented in this study are addressed in a second paper exploring the ethynyl (C2H) radical’s ground X 2Σ+ state and low-lying A 2Π state as well as its anionic form, the acetylide anion (C2H−). Special basis sets designed to treat diffuse (dipole-bound) states are developed in the final chapter which lays the foundation for the treatment of larger systems, such as anions, that posses dipole-bound excited states.</p>","abstract_has_math":false,"creators":["Morgan, Whitney J","Fortenberry, Ryan C"],"institution":null,"degree_name":"Master of Science in Applied Physical Science (M.S.)","degree_level":"Thesis (restricted to Georgia Southern)","degree_discipline":"Department of Chemistry","degree_department":null,"school":null,"contributors":["Sarah Higdon","James LoBue"],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2015,"date_issued":"2015-01-01T08:00:00Z","date_published":"2015-01-01T08:00:00Z","updated_at":"2026-07-24T02:28:22Z","subjects":["ETD","astrochemistry","coupled cluster","dipole bound","excited state","quartic force field","rovibrational spectroscopy","Atomic, Molecular and Optical Physics","Physical Chemistry","Stars, Interstellar Medium and the Galaxy"],"languages":[],"rights":[],"rights_urls":[],"identifier_entries":[]},"links":{"outbound_url":"https://digitalcommons.georgiasouthern.edu/etd/1251","outbound_label":"Repository record","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Sarah Higdon","James LoBue"]},{"key":"dc:creator","label":"Author","values":["Morgan, Whitney J","Fortenberry, Ryan C"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date.available","label":"Dc Date Available","values":["2016-04-22T07:00:00Z"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Department of Chemistry"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Thesis (restricted to Georgia Southern)"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Master of Science in Applied Physical Science (M.S.)"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["ETD","astrochemistry","coupled cluster","dipole bound","excited state","quartic force field","rovibrational spectroscopy","Atomic, Molecular and Optical Physics","Physical Chemistry","Stars, Interstellar Medium and the Galaxy"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["https://digitalcommons.georgiasouthern.edu/etd/1251"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description.abstract","label":"Abstract","values":["Theoretical chemistry has advanced to the point where spectroscopic data can be produced that is directly comparable to high-accuracy experimental results. Quartic force field (QFFs) methods are one of the most efficient means of generating this data and have even shown spectroscopic accuracy (±1 cm−1) for fundamental vibrational frequencies. A method for extending QFFs to variationally inaccessible electronically excited states is presented herein using equation-of-motion (EOM) coupled cluster theory. The new EOM-based QFF is tested against the traditional QFF method using the isoformyl (HOC) radical’s variationally accessible 1 A” excited state and compared to previous benchmark studies. Challenges presented in this study are addressed in a second paper exploring the ethynyl (C2H) radical’s ground X 2Σ+ state and low-lying A 2Π state as well as its anionic form, the acetylide anion (C2H−). Special basis sets designed to treat diffuse (dipole-bound) states are developed in the final chapter which lays the foundation for the treatment of larger systems, such as anions, that posses dipole-bound excited states.
"]},{"key":"dc:title","label":"Title","values":["Quartic Force Fields for Electronically Excited States of Interstellar Molecules"]}]}],"canonical_facts":{"dc:contributor":["Sarah Higdon","James LoBue"],"dc:creator":["Morgan, Whitney J","Fortenberry, Ryan C"],"dc:date.available":["2016-04-22T07:00:00Z"],"dc:description.abstract":["Theoretical chemistry has advanced to the point where spectroscopic data can be produced that is directly comparable to high-accuracy experimental results. Quartic force field (QFFs) methods are one of the most efficient means of generating this data and have even shown spectroscopic accuracy (±1 cm−1) for fundamental vibrational frequencies. A method for extending QFFs to variationally inaccessible electronically excited states is presented herein using equation-of-motion (EOM) coupled cluster theory. The new EOM-based QFF is tested against the traditional QFF method using the isoformyl (HOC) radical’s variationally accessible 1 A” excited state and compared to previous benchmark studies. Challenges presented in this study are addressed in a second paper exploring the ethynyl (C2H) radical’s ground X 2Σ+ state and low-lying A 2Π state as well as its anionic form, the acetylide anion (C2H−). Special basis sets designed to treat diffuse (dipole-bound) states are developed in the final chapter which lays the foundation for the treatment of larger systems, such as anions, that posses dipole-bound excited states.
"],"dc:identifier":["https://digitalcommons.georgiasouthern.edu/etd/1251"],"dc:subject":["ETD","astrochemistry","coupled cluster","dipole bound","excited state","quartic force field","rovibrational spectroscopy","Atomic, Molecular and Optical Physics","Physical Chemistry","Stars, Interstellar Medium and the Galaxy"],"dc:title":["Quartic Force Fields for Electronically Excited States of Interstellar Molecules"],"thesis:degree_discipline":["Department of Chemistry"],"thesis:degree_level":["Thesis (restricted to Georgia Southern)"],"thesis:degree_name":["Master of Science in Applied Physical Science (M.S.)"]},"updated_at":"2026-07-24T02:28:22Z"}