Submitted by Sandra Pereira (srpereira@ufrrj.br) on 2017-01-20T11:19:55Z No. of bitstreams: 1 2016 - Michel Braga Garcia.pdf: 2199692 bytes, checksum: 4e890f95e489a3e9ea5a095b493dce78 (MD5) / Made available in DSpace on 2017-01-20T11:19:55Z (GMT). No. of bitstreams: 1 2016 - Michel Braga Garcia.pdf: 2199692 bytes, checksum: 4e890f95e489a3e9ea5a095b493dce78 (MD5) Previous issue date: 2016-04-06 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior - CAPES / Studies on Atmospheric Chemistry allow the understanding of chemical behavior of different atmospheric pollutants towards oxidant agents in troposphere. Among these agents, OH radicals, ozone and nitrate radicals are the most important. In coastal zones, chlorine atoms are also important specie for the chemical removal of primary and secondary pollutants. This work aims the kinetic study of the gas phase reaction between chlorine atom and formaldehyde, H2CO + Cl ? HCO + HCl. The reaction was described at HF, MP2, CCSD, QCISD and DFT (B2PLYP, MPW2PLYP and MPWKCIS1K) levels. Basis set effect was also explored and the aug-cc-pVDZ (ACCD) and aug-cc-pVTZ (ACCT) basis set were adopted. Geometry optimizations and vibrational frequencies calculations were performed for reactants and products. A prebarrier complex was located at all levels of theory, stabilized with respect the isolated reactants by ca. 4 kcal mol-1. Saddle points were located and characterized by their imaginary frequencies. Energy barriers were predicted as ca. 1 kcal mol-1, in agreement with experimental results (0.7 ? 1.0 kcal mol-1). Rate coefficients were calculated in the range from 100 to 500 K, adopting the canonical variational method, as available in the kcvt code. The calculated kinetic parameters, rate coefficients (k, 298 K, expressed in 10-11 cm3 molecule-1 s-1), activation energy (Ea, expressed in kcal mol-1) and Arrhenius preexponential factor (A, expressed in 10-11 cm3 molecule-1 s-1) were: k = 4.89, Ea = 0.25 and A = 7.45. The results suggest that a reaction dynamics is well described by a mechanism taking into account a prebarrier intermediate. Canonical variational rate coefficients were predicted in good agreement with experimental data, validating the proposal for the reaction mechanism introduced in this study / Os estudos em Qu?mica Atmosf?rica permitem entender o comportamento qu?mico de diversos poluentes atmosf?ricos frente a agentes oxidantes presentas na troposfera. Entre esses agentes, radicais OH, oz?nio e nitrato s?o os mais importantes. Ainda em zonas costeiras, ?tomos de cloro tornam-se tamb?m importantes esp?cies para a remo??o qu?mica de poluentes prim?rios e secund?rios. Este trabalho visa o estudo cin?tico da rea??o H2CO + Cl ? HCO + HCl em fase gasosa. A rea??o foi descrita em n?veis HF, MP2, CCSD, QCISD, DFT (B2PLYP, MPW2PLYP e MPWKCIS1K) Tamb?m o efeito da base foi explorado e, para tanto, as bases aug-cc-pVDZ (ACCD) e aug-cc-pVTZ (ACCT) foram adotadas. C?lculos de otimiza??o de geometria e frequ?ncia vibracionais foram feitos para reagentes e produtos. Foram vistos tamb?m para todos os n?veis de c?lculo a forma??o de um pr?-complexo estabilizado, em rela??o aos reagentes isolados, por cerca de 4 kcal mol-1. Ponto de sela tamb?m foram otimizados e identificados pela frequ?ncia vibracional imagin?ria. Barreiras de energia foram previstas em cerca de 1 kcal mol-1, em acordo com a previs?o da literatura, 0,7 - 1,0 kcal mol-1. Os coeficientes de velocidade foram calculados na faixa de 100 ? 500 K a partir da teoria do estado de transi??o variacional com auxilio do programa kcvt. Os par?metros cin?ticos encontrados, coeficientes de velocidade (k, 298 K, expressos em 10-11 cm3mol?cula-1s-1), energia de ativa??o (Ea, expresso em kcal mol-1) e fator pr?-exponencial (A, expresso em 10-11 cm3mol?cula-1s-1) foram: k298K = 4,89, Ea = 0,25 e A = 7,45. Os resultados sugerem que a din?mica da rea??o ? bem descrita a partir de um mecanismo que contempla a participa??o de um intermedi?rio pr?-barreira. Resultados de coeficientes de velocidade variacionais can?nicos obtidos neste trabalho se mostraram satisfat?rios quando comparados a dados experimentais validando a proposta de mecanismo trazida nesse trabalho.