Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica
Autor(a) principal: | |
---|---|
Data de Publicação: | 2021 |
Tipo de documento: | Dissertação |
Idioma: | por |
Título da fonte: | Biblioteca Digital de Teses e Dissertações da UFPB |
Texto Completo: | https://repositorio.ufpb.br/jspui/handle/123456789/21129 |
Resumo: | Chlorofluorocarbons (CFCs) are synthetic compounds that have been very used in refrigeration systems, due to their great chemical stability. Nowadays, these compounds are known because they have an important contribution to reducing the concentration of stratospheric ozone. Although the use of CFCs was limited by the Montreal Protocol, the presence of these molecules in the atmosphere is a secular concern, in other words, they will react for a long time in atmosphere. Based on these facts, the importance of this work relies on the need for a better understanding of the photodissociative processes involving these compounds in atmosphere. Dichlorodifluoromethane (CF2Cl2), also known as CFC-12, was chosen in this study because it is one of the most abundant CFCs and it has a long-term life around 112 years. In addition, it has a high ozone depletion potential. Although the electronic structure of the molecule has been previously investigated, some mechanisms are still not understood. Therefore, the objective of this research was to investigate how properties of 25 excited singles states of valence and Rydberg, through calculations of electronic structure, as well as a photodissociation of the molecule, from the characterization of the Potential Energy Curves (PEC). For this, computational tools were used, such as the highly correlated methods MCSCF (CASSCF) and MR-CISD/MR-CISD+Q, performed with the COLUMBUS 7.0 program. An experimental geometry was used as a starting point for the calculations. The CAS (12.8) and CAS (12.12) active spaces were used, and the aug-cc-pVDZ and d-aug-ccpVDZ base sets. The results showed the importance of Rydberg states for this system because the inclusion of these states provided a better characterization of electronic transitions. The MR-CISD method, with the MR-CISD+Q extensibility correction, provided better results for the investigated states. The theoretical results obtained for the values of the vertical energies of the valence states were in good agreement with that observed experimentally. PEC revealed the existence of a local dissociative minimum in the 31A' state curve that favors the formation of the CF2Cl+ (11A') + Cl- (1S) ion channel, based on non-adiabatic events. Optimization and frequency calculations confirmed the structure of the [CF2Cl]+ Cl- pair, with a stability of 3.64 eV. It was possible to conclude that the study achieved the objectives proposed in its initial planning. It is hoped that this research will enable a better understanding of the photochemistry of the CF2Cl2 molecule. |
id |
UFPB_dc97cdb4e42a2992795cd0ea6554d03c |
---|---|
oai_identifier_str |
oai:repositorio.ufpb.br:123456789/21129 |
network_acronym_str |
UFPB |
network_name_str |
Biblioteca Digital de Teses e Dissertações da UFPB |
repository_id_str |
|
spelling |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônicaCFCEstados excitadosEstado iônicoFotodissociaçãoMétodos correlacionadosExcited statesIonic statePhotodissociationCorrelated methodsCNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICAChlorofluorocarbons (CFCs) are synthetic compounds that have been very used in refrigeration systems, due to their great chemical stability. Nowadays, these compounds are known because they have an important contribution to reducing the concentration of stratospheric ozone. Although the use of CFCs was limited by the Montreal Protocol, the presence of these molecules in the atmosphere is a secular concern, in other words, they will react for a long time in atmosphere. Based on these facts, the importance of this work relies on the need for a better understanding of the photodissociative processes involving these compounds in atmosphere. Dichlorodifluoromethane (CF2Cl2), also known as CFC-12, was chosen in this study because it is one of the most abundant CFCs and it has a long-term life around 112 years. In addition, it has a high ozone depletion potential. Although the electronic structure of the molecule has been previously investigated, some mechanisms are still not understood. Therefore, the objective of this research was to investigate how properties of 25 excited singles states of valence and Rydberg, through calculations of electronic structure, as well as a photodissociation of the molecule, from the characterization of the Potential Energy Curves (PEC). For this, computational tools were used, such as the highly correlated methods MCSCF (CASSCF) and MR-CISD/MR-CISD+Q, performed with the COLUMBUS 7.0 program. An experimental geometry was used as a starting point for the calculations. The CAS (12.8) and CAS (12.12) active spaces were used, and the aug-cc-pVDZ and d-aug-ccpVDZ base sets. The results showed the importance of Rydberg states for this system because the inclusion of these states provided a better characterization of electronic transitions. The MR-CISD method, with the MR-CISD+Q extensibility correction, provided better results for the investigated states. The theoretical results obtained for the values of the vertical energies of the valence states were in good agreement with that observed experimentally. PEC revealed the existence of a local dissociative minimum in the 31A' state curve that favors the formation of the CF2Cl+ (11A') + Cl- (1S) ion channel, based on non-adiabatic events. Optimization and frequency calculations confirmed the structure of the [CF2Cl]+ Cl- pair, with a stability of 3.64 eV. It was possible to conclude that the study achieved the objectives proposed in its initial planning. It is hoped that this research will enable a better understanding of the photochemistry of the CF2Cl2 molecule.Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPqOs clorofluorcarbonos (CFCs) são compostos sintéticos que foram amplamente utilizados em sistemas de refrigeração, devido a sua grande estabilidade química. Atualmente, esses compostos são reconhecidos por contribuírem significativamente na redução da concentração do ozônio estratosférico. Embora o uso dos CFCs tenha sido limitado pelo Protocolo de Montreal, a permanência dessas moléculas na atmosfera é da ordem secular, ou seja, reagirão por um longo período na atmosfera. Nesta conjuntura, a relevância desta pesquisa recai na necessidade de uma melhor compreensão dos processos fotodissociativos dessas substâncias em meio atmosférico. O diclorodifluorometano (CF2Cl2), também conhecido como CFC-12, foi a molécula escolhida neste estudo, por ser um dos CFCs mais abundantes e possuir uma vida útil de cerca de 112 anos. Além disso, possui um alto potencial de depleção do ozônio. Embora que a estrutura eletrônica da molécula já tenha sido previamente investigada, alguns mecanismos ainda não são bem compreendidos. Sendo assim, o objetivo dessa pesquisa foi investigar as propriedades de 25 estados excitados singletos de valência e Rydberg, através de cálculos de estrutura eletrônica, bem como a fotodissociação da molécula, a partir da caracterização das Curvas de Energia Potencial (CEP). Para tal, foram utilizadas ferramentas computacionais como os métodos altamente correlacionados MCSCF (CASSCF) e MRCISD/ MR-CISD+Q, realizados com o programa COLUMBUS 7.0. Uma geometria experimental foi utilizada como ponto de partida para os cálculos. Foram utilizados os espaços ativos CAS (12,8) e CAS (12,12), e os conjuntos de base aug-cc-pVDZ e d-aug-ccpVDZ. Os resultados revelaram a importância dos estados de Rydberg para este sistema, pois a inclusão desses estados forneceu uma boa caracterização das transições eletrônicas. O método MR-CISD, com a correção de extensividade MR-CISD+Q, forneceu melhores resultados para os estados investigados. Os resultados teóricos obtidos para os valores das energias verticais dos estados de valência estiveram em boa concordância com o observado experimentalmente. As CEP revelaram a existência de um mínimo local dissociativo na curva do estado 31A' que favorece a formação do canal iônico CF2Cl+ (11A') + Cl- (1S), a partir de eventos não adiabáticos. Cálculos de otimização e frequências confirmaram a estrutura do par [CF2Cl]+Cl-, com uma estabilidade de 3,64 eV. Pode-se concluir que o estudo alcançou os objetivos propostos no seu planejamento inicial. Espera-se que essa pesquisa possibilite um melhor entendimento da fotoquímica da molécula CF2Cl2.Universidade Federal da ParaíbaBrasilQuímicaPrograma de Pós-Graduação em QuímicaUFPBFaustino, Wagner de Mendonçahttp://lattes.cnpq.br/4969484654273225Monte, Elizete Ventura dohttp://lattes.cnpq.br/0792089842728963Monte, Silmar Andrade dohttp://lattes.cnpq.br/7082181076432469Nascimento, Mayzza Márcia Araujo do2021-09-30T21:34:50Z2021-03-032021-09-30T21:34:50Z2021-02-19info:eu-repo/semantics/publishedVersioninfo:eu-repo/semantics/masterThesishttps://repositorio.ufpb.br/jspui/handle/123456789/21129porAttribution-NoDerivs 3.0 Brazilhttp://creativecommons.org/licenses/by-nd/3.0/br/info:eu-repo/semantics/openAccessreponame:Biblioteca Digital de Teses e Dissertações da UFPBinstname:Universidade Federal da Paraíba (UFPB)instacron:UFPB2022-08-09T17:47:29Zoai:repositorio.ufpb.br:123456789/21129Biblioteca Digital de Teses e Dissertaçõeshttps://repositorio.ufpb.br/PUBhttp://tede.biblioteca.ufpb.br:8080/oai/requestdiretoria@ufpb.br|| diretoria@ufpb.bropendoar:2022-08-09T17:47:29Biblioteca Digital de Teses e Dissertações da UFPB - Universidade Federal da Paraíba (UFPB)false |
dc.title.none.fl_str_mv |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
title |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
spellingShingle |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica Nascimento, Mayzza Márcia Araujo do CFC Estados excitados Estado iônico Fotodissociação Métodos correlacionados Excited states Ionic state Photodissociation Correlated methods CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA |
title_short |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
title_full |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
title_fullStr |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
title_full_unstemmed |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
title_sort |
Estudo teórico da fotodissociação da molécula diclorodifluorometano (CFC 12) aplicando métodos multiconfiguracionais de estrutura eletrônica |
author |
Nascimento, Mayzza Márcia Araujo do |
author_facet |
Nascimento, Mayzza Márcia Araujo do |
author_role |
author |
dc.contributor.none.fl_str_mv |
Faustino, Wagner de Mendonça http://lattes.cnpq.br/4969484654273225 Monte, Elizete Ventura do http://lattes.cnpq.br/0792089842728963 Monte, Silmar Andrade do http://lattes.cnpq.br/7082181076432469 |
dc.contributor.author.fl_str_mv |
Nascimento, Mayzza Márcia Araujo do |
dc.subject.por.fl_str_mv |
CFC Estados excitados Estado iônico Fotodissociação Métodos correlacionados Excited states Ionic state Photodissociation Correlated methods CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA |
topic |
CFC Estados excitados Estado iônico Fotodissociação Métodos correlacionados Excited states Ionic state Photodissociation Correlated methods CNPQ::CIENCIAS EXATAS E DA TERRA::QUIMICA |
description |
Chlorofluorocarbons (CFCs) are synthetic compounds that have been very used in refrigeration systems, due to their great chemical stability. Nowadays, these compounds are known because they have an important contribution to reducing the concentration of stratospheric ozone. Although the use of CFCs was limited by the Montreal Protocol, the presence of these molecules in the atmosphere is a secular concern, in other words, they will react for a long time in atmosphere. Based on these facts, the importance of this work relies on the need for a better understanding of the photodissociative processes involving these compounds in atmosphere. Dichlorodifluoromethane (CF2Cl2), also known as CFC-12, was chosen in this study because it is one of the most abundant CFCs and it has a long-term life around 112 years. In addition, it has a high ozone depletion potential. Although the electronic structure of the molecule has been previously investigated, some mechanisms are still not understood. Therefore, the objective of this research was to investigate how properties of 25 excited singles states of valence and Rydberg, through calculations of electronic structure, as well as a photodissociation of the molecule, from the characterization of the Potential Energy Curves (PEC). For this, computational tools were used, such as the highly correlated methods MCSCF (CASSCF) and MR-CISD/MR-CISD+Q, performed with the COLUMBUS 7.0 program. An experimental geometry was used as a starting point for the calculations. The CAS (12.8) and CAS (12.12) active spaces were used, and the aug-cc-pVDZ and d-aug-ccpVDZ base sets. The results showed the importance of Rydberg states for this system because the inclusion of these states provided a better characterization of electronic transitions. The MR-CISD method, with the MR-CISD+Q extensibility correction, provided better results for the investigated states. The theoretical results obtained for the values of the vertical energies of the valence states were in good agreement with that observed experimentally. PEC revealed the existence of a local dissociative minimum in the 31A' state curve that favors the formation of the CF2Cl+ (11A') + Cl- (1S) ion channel, based on non-adiabatic events. Optimization and frequency calculations confirmed the structure of the [CF2Cl]+ Cl- pair, with a stability of 3.64 eV. It was possible to conclude that the study achieved the objectives proposed in its initial planning. It is hoped that this research will enable a better understanding of the photochemistry of the CF2Cl2 molecule. |
publishDate |
2021 |
dc.date.none.fl_str_mv |
2021-09-30T21:34:50Z 2021-03-03 2021-09-30T21:34:50Z 2021-02-19 |
dc.type.status.fl_str_mv |
info:eu-repo/semantics/publishedVersion |
dc.type.driver.fl_str_mv |
info:eu-repo/semantics/masterThesis |
format |
masterThesis |
status_str |
publishedVersion |
dc.identifier.uri.fl_str_mv |
https://repositorio.ufpb.br/jspui/handle/123456789/21129 |
url |
https://repositorio.ufpb.br/jspui/handle/123456789/21129 |
dc.language.iso.fl_str_mv |
por |
language |
por |
dc.rights.driver.fl_str_mv |
Attribution-NoDerivs 3.0 Brazil http://creativecommons.org/licenses/by-nd/3.0/br/ info:eu-repo/semantics/openAccess |
rights_invalid_str_mv |
Attribution-NoDerivs 3.0 Brazil http://creativecommons.org/licenses/by-nd/3.0/br/ |
eu_rights_str_mv |
openAccess |
dc.publisher.none.fl_str_mv |
Universidade Federal da Paraíba Brasil Química Programa de Pós-Graduação em Química UFPB |
publisher.none.fl_str_mv |
Universidade Federal da Paraíba Brasil Química Programa de Pós-Graduação em Química UFPB |
dc.source.none.fl_str_mv |
reponame:Biblioteca Digital de Teses e Dissertações da UFPB instname:Universidade Federal da Paraíba (UFPB) instacron:UFPB |
instname_str |
Universidade Federal da Paraíba (UFPB) |
instacron_str |
UFPB |
institution |
UFPB |
reponame_str |
Biblioteca Digital de Teses e Dissertações da UFPB |
collection |
Biblioteca Digital de Teses e Dissertações da UFPB |
repository.name.fl_str_mv |
Biblioteca Digital de Teses e Dissertações da UFPB - Universidade Federal da Paraíba (UFPB) |
repository.mail.fl_str_mv |
diretoria@ufpb.br|| diretoria@ufpb.br |
_version_ |
1801842982080479232 |