Theoretical study of the electronic spectrum of disulfur monoxide

The near ultraviolet-visible absorption spectrum of disulfur monoxide (S2O) has been theoretically studied by using the time-dependent density functional theory (TD-DFT) and the equation of motion coupled-cluster singles and doubles approach (EOM-CCSD) combined with the AUG-cc-PVQZ basis set. From this, analytical expressions for the absorption coefficient over the 250 - 340 nm range are reported for the first time. The computed molecular structure and the vibrational frequencies for the ground and third electronically excited state S2O (C1A′), responsible of the observed spectrum, are compared with available data.Facultad de Ciencias ExactasInstituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Theoretical Study of the Absorption Spectrum and the Thermochemistry of the CF3OSO3 Radical

The UV-visible absorption spectrum of the recently reported CF3OSO3 radical has been studied by using the time-dependent generalization of the density functional theory (TDDFT). For this a set of eleven hybrid functionals combined with the 6-311+G(3df) basis set were employed. The main features of the three experimental absorption bands of CF3OSO3 recorded over the 220-530 nm range are well reproduced by the calculations. A dissociation enthalpy for the CF3O-SO3 bond of 19.1 kcal mol-1 is predicted at the BAC-G3MP2//B3LYP/6-311+G(3df) level of theory.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Theoretical Study of the Absorption Spectrum and the Thermochemistry of the CF3OSO3 Radical

The UV-visible absorption spectrum of the recently reported CF3OSO3 radical has been studied by using the time-dependent generalization of the density functional theory (TDDFT). For this a set of eleven hybrid functionals combined with the 6-311+G(3df) basis set were employed. The main features of the three experimental absorption bands of CF3OSO3 recorded over the 220-530 nm range are well reproduced by the calculations. A dissociation enthalpy for the CF3O-SO3 bond of 19.1 kcal mol-1 is predicted at the BAC-G3MP2//B3LYP/6-311+G(3df) level of theory.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

A SACM study of the cross-combination ratio of rate constants

An analysis of the cross-combination ratio of the rate constants ϕ in terms of the statistical adiabatic channel model allows to factorize ϕ into two contributions: one due to the motion along the reaction coordinates and another due to the reaction transitional modes. ϕ for the CH3/CCl3, CH3/C2H3, CH3/C3H5, CH3/C2H5 and C2H5/C3H5 radical pairs were calculated.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Estudio de la descomposición fotoquímica del ozono

El ozono es una de las moléculas mus interesantes de la química inorgánica. Es muy reactivo y participa por eso en numerosas reacciones térmicas y fotoquímicas. Desde el punto de vista fotoquímico tiene un interés especial porque el estado electrónico de los productos de la disociación que sigue a la absorción de un fotón depende de la longitud de onda de la radiación absorbida. Esto permite estudiar el comportamiento químico de especies con distinto grado de excitación puesto que tanto el oxígeno atómico como el molecular poseen estados electrónicos excitados relativamente fáciles de alcanzar. También presenta un interés especial desde un punto de vista práctico. Se sabe que el ozono es un componente normal de la alta atmósfera que impide que radiaciones de longitudes de onda menores a 310 nm lleguen a la superficie de la Tierra. Estas radiaciones tienen un efecto letal sobre la vida terrestre.Tesis digitalizada en SEDICI gracias a la colaboración de la Biblioteca de la Facultad de Ciencias Exactas (UNLP).Facultad de Ciencias Exacta

Limiting high pressure rate coefficients for the HO+NO2&→HONO2 reaction on ab initio potential energy surfaces

Phase space limiting high pressure rate coefficients for the title reaction on ab initio potential energy surfaces have been calculated at 50-600 K. Calculated rigidity factors at different levels of theory are presented. The best limiting high pressure rate coefficient obtained at 300 K, 4.0x10-11cm3 molecule-1 s-1, compares very well with the latest IUPAC recommended value.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Shock wave study and theoretical modeling of the thermal decomposition of c-C4F8

The thermal dissociation of octafluorocyclobutane, c-C4F8, was studied in shock waves over the range 1150-2300 K by recording UV absorption signals of CF2. It was found that the primary reaction nearly exclusively produces 2 C2F4 which afterwards decomposes to 4 CF2. A primary reaction leading to CF2 + C3F6 is not detected (an upper limit to the yield of the latter channel was found to be about 10 percent). The temperature range of earlier single pulse shock wave experiments was extended. The reaction was shown to be close to its high pressure limit. Combining high and low temperature results leads to a rate constant for the primary dissociation of k1 = 1015.97 exp(-310.5 kJ mol-1/RT) s-1 in the range 630-1330 K, over which k1 varies over nearly 14 orders of magnitude. Calculations of the energetics of the reaction pathway and the rate constants support the conclusions from the experiments. Also they shed light on the role of the 1,4-biradical CF2CF2CF2CF2 as an intermediate of the reaction.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Hintzer, K.. Dyneon Gmbh; AlemaniaFil: Sölter, L.. Universität Göttingen; AlemaniaFil: Tellbach, E.. Universität Göttingen; AlemaniaFil: Thaler, A.. Dyneon Gmbh; AlemaniaFil: Troe, J.. Universität Göttingen; Alemania. Max-Planck-Institut fu¨r biophysikalische Chemie; Alemani

Theoretical determination of the rate constant of the CCl2 + CCl2 → C2Cl4 association reaction

En un estudio previo se determinó la constante de velocidad de la reacción CCl2+CCl2 → C2Cl4 empleando la técnica de fluorescencia inducida por láser. En el presente trabajo determinamos mediante el modelo de los canales estadísticamente adiabáticos la constante de velocidad de este proceso en el régimen de alta presión. Se empleó la teoría del funcional de la densidad para determinar las propiedades moleculares de los reactivos y del complejo activado. Entre 300 K y 2000 K se obtuvo la siguiente expresión k∞ = (1,5 ± 0,4) x 10-12 x (T / 300K) (0.50±0.07) exp[-(260 ± 10) K/T] cm3 molécula-1 s-1. El valor a temperatura ambiente está en muy buen acuerdo con el valor experimental determinado en nuestro laboratorio.In a previous work we used the laser induced fluorescence technique to determine the rate constant of the CCl2 + CCl2 association reaction. In the present work we determined by the statistical adiabatic channel model the temperature dependence of the rate constant in the high pressure regime. The density functional theory was used to characterize the properties of the parent molecules and the activated complex. Within 300 K and 2000 K we obtained the following expression k∞ = (1,5 ± 0,4) x 10-12 x (T / 300K)(0.50±0.07) exp[- (260 ± 10) K/T] cm3 molécula-1 s-1. The value at room temperature is in very good agreement with the experimental value obtained in our laboratory.Fil: Gómez, Nicolás Damián. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; ArgentinaFil: Azcárate, María Laura. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; ArgentinaFil: Codnia, Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Unidad de Investigación y Desarrollo Estratégico para la Defensa. Ministerio de Defensa. Unidad de Investigación y Desarrollo Estratégico para la Defensa; ArgentinaFil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; Argentin

Theoretical modeling study of the reaction H + CF4 → HF + CF3

The high-temperature hydrogenation of CF4 in mixtures of CF4 and H2 is assumed to involve the reaction H + CF4 → HF + CF3. The hydrogen atoms here are either formed by the reaction of F and CF3 (i.e., the products of the thermal dissociation of CF4) with H2, or by the thermal dissociation of H2. In the former case, a complicated chain process is started, while the reaction proceeds in a more direct way in the latter. This article determines the rate constant of the reaction H + CF4 → HF + CF3, characterizing its transition state by quantum-chemical methods. Over the temperature range 1000–3000 K, the most accurate results for the rate constant can be represented in the form 1.64 × 1014 (T/1000 K)1.95 exp(−178.8 kJ mol–1/RT) cm3 mol–1 s–1, based on coupled cluster theory extrapolated to the complete basis set limit, and incorporating vibrational anharmonicity, electron correlation through CCSDT(Q), and relativistic and non-Born–Oppenheimer effects.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Knight, Gary. Edwards Innovation Centre; Reino UnidoFil: Marshall, Paul. University of North Texas; Estados UnidosFil: Troe, Jürgen. Universität Göttingen; Alemani

Falloff curves and mechanism of thermal decomposition of CF3I in shock waves

The falloff curves of the unimolecular dissociation CF3I (+Ar) - CF3 + I (+Ar) are modelled by combining quantum-chemical characterizations of the potential energy surface for the reaction, standard unimolecular rate theory, and experimental information on the average energy transferred per collision between excited CF3I and Ar. The (essentially) parameter-free theoretical modelling gives results in satisfactory agreement with data deduced from earlier shock wave experiments employing a variety of reactant concentrations (between a few ppm and a few percent in the bath gas Ar). New experiments recording absorption–time signals of CF3I, I2, CF2 and (possibly) IF at 450–500 and 200–300 nm are reported. By analysing the decomposition mechanism, besides the unimolecular dissociation of CF3I, these provide insight into the influence of secondary reactions on the experimental observations.Fil: Cobos, Carlos Jorge. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas. Universidad Nacional de La Plata. Facultad de Ciencias Exactas. Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicadas; ArgentinaFil: Sölter, L.. Universität Göttingen; AlemaniaFil: Tellbach, E.. Universität Göttingen; AlemaniaFil: Troe, J.. Universität Göttingen; Alemania. Institut Max Planck fuer Bioanorganische Chemie; Alemani