scholarly journals Isotope effects in N<sub>2</sub>O photolysis from first principles

2011 ◽  
Vol 11 (5) ◽  
pp. 16075-16105 ◽  
Author(s):  
J. A. Schmidt ◽  
M. S. Johnson ◽  
R. Schinke
Keyword(s):  
Experimental Data ◽  
Cross Sections ◽  
First Principles ◽  
Potential Energy Surfaces ◽  
Ad Hoc ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Energy Surfaces ◽  
First Time ◽  
Wavepacket Propagation

Abstract. For the first time, accurate potential energy surfaces allow N2O cross sections and isotopic fractionation spectra to be derived that are in agreement with available experimental data (without ad hoc shifting), extending knowledge to a much broader range of conditions. Absorption spectra of rare N- and O-isotopologues (15N14N16O, 14N15N16O, 15N216O, 14N217O and 14N218O) calculated using wavepacket propagation are compared to the most abundant isotopologue (14N216O). The fractionation constants as a function of wavelength and temperature are in excellent agreement with experimental data. The study shows that excitations from the 3rd excited bending state, (0,3,0), and the first combination band, (1,1,0), are important for explaining the isotope effect at wavelengths longer than 210 nm. Only a small amount of the mass independent oxygen isotope anomaly observed in atmospheric N2O samples can be explained as arising from photolysis.

scholarly journals Isotope effects in N<sub>2</sub>O photolysis from first principles

2011 ◽  
Vol 11 (17) ◽  
pp. 8965-8975 ◽  
Author(s):  
J. A. Schmidt ◽  
M. S. Johnson ◽  
R. Schinke
Keyword(s):  
Experimental Data ◽  
Potential Energy ◽  
Cross Sections ◽  
First Principles ◽  
Potential Energy Surfaces ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Energy Surfaces ◽  
First Time ◽  
Wavepacket Propagation

Abstract. For the first time, accurate first principles potential energy surfaces allow N2O cross sections and isotopic fractionation spectra to be derived that are in agreement with all available experimental data, extending our knowledge to a much broader range of conditions. Absorption spectra of rare N- and O-isotopologues (15N14N16O, 14N15N16O, 15N216O, 14N217O and 14N218O) calculated using wavepacket propagation are compared to the most abundant isotopologue (14N216O). The fractionation constants as a function of wavelength and temperature are in excellent agreement with experimental data. The study shows that excitations from the 3rd excited bending state, (0,3,0), and the first combination state, (1,1,0), are important for explaining the isotope effect at wavelengths longer than 210 nm. Only a small amount of the mass independent oxygen isotope anomaly observed in atmospheric N2O samples can be explained as arising from photolysis.

scholarly journals On the isotopic fingerprint exerted on carbonyl sulfide by the stratosphere

2012 ◽  
Vol 12 (9) ◽  
pp. 25329-25353 ◽  
Author(s):  
J. A. Schmidt ◽  
S. Hattori ◽  
N. Yoshida ◽  
S. Nanbu ◽  
M. S. Johnson ◽  
...  
Keyword(s):  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Carbonyl Sulfide ◽  
Isotopic Fractionation ◽  
Data Sets ◽  
Mechanical Formalism ◽  
Model Study ◽  
Quantum Mechanical Formalism ◽  
Energy Surfaces ◽  
Good Agreement

Abstract. The isotopic fractionation in OCS photolysis is studied theoretically from first principles. UV absorption cross sections for OCS, OC33S, OC34S, OC36S and O13CS are calculated using the time-depedent quantum mechanical formalism and recent potential energy surfaces for the lowest four singlet and lowest four triplet electronic states. The calculated isotopic fractionations as a function of wavelength are in good agreement with recent measurements by Hattori et al. (2011) and indicate that photolysis leads to only a small enrichment of 34S in the remaining pool of OCS. A simple stratospheric model is constructed taking into account the main stratospheric sink reactions of OCS and it is found that stratospheric removal overall slightly favors light OCS in constrast to the findings of Leung et al. (2002). These results show, based on isotopic considerations, that OCS is an acceptable source of background stratosperic sulfate aerosol in agreement with a recent model study of Brühl et al. (2012). The 13C isotopic fractionation due to photolysis of OCS is significant and will leave a strong signal in the pool of remaining OCS making it a candidate for tracing using the ACE-FTS and MIPAS data sets.

scholarly journals OCS photolytic isotope effects from first principles: sulfur and carbon isotopes, temperature dependence and implications for the stratosphere

2013 ◽  
Vol 13 (3) ◽  
pp. 1511-1520 ◽  
Author(s):  
J. A. Schmidt ◽  
M. S. Johnson ◽  
S. Hattori ◽  
N. Yoshida ◽  
S. Nanbu ◽  
...  
Keyword(s):  
Cross Sections ◽  
First Principles ◽  
Isotope Effects ◽  
Isotopic Fractionation ◽  
Data Sets ◽  
Mechanical Formalism ◽  
Model Study ◽  
Quantum Mechanical Formalism ◽  
Uv Excitation ◽  
Good Agreement

Abstract. The isotopic fractionation in OCS photolysis is studied theoretically from first principles. UV absorption cross sections for OCS, OC33S, OC34S, OC36S and O13CS are calculated using the time-depedent quantum mechanical formalism and a recently developed ab-initio description of the photodissociation of OCS which takes into account the lowest four singlet and lowest four triplet electronic states. The calculated isotopic fractionations as a function of wavelength are in good agreement with recent measurements by Hattori et al. (2011) and indicate that photolysis leads to only a small enrichment of 34S in the remaining OCS. The photodissociation dynamics provide strong evidence that the photolysis quantum yield is unity at all wavelengths for atmospheric UV excitation, for all isotopologues. A simple stratospheric model is constructed taking into account the main sink reactions of OCS and it is found that overall stratospheric removal slightly favors light OCS in constrast to the findings of Leung et al. (2002). These results show, based on isotopic considerations, that OCS is an acceptable source of background stratosperic sulfate aerosol in agreement with a recent model study of of Brühl et al. (2012). The 13C isotopic fractionation due to photolysis of OCS in the upper stratosphere is significant and will leave a clear signal in the remaining OCS making it a candidate for tracing using the ACE-FTS and MIPAS data sets.

Global investigation of potential energy surfaces for the pyrolysis of C1–C3 hydrocarbons: toward the development of detailed kinetic models from first principles

2015 ◽  
Vol 17 (41) ◽  
pp. 27789-27805 ◽  
Author(s):  
Mikhail N. Ryazantsev ◽  
Adeel Jamal ◽  
Satoshi Maeda ◽  
Keiji Morokuma
Keyword(s):  
Potential Energy ◽  
First Principles ◽  
Kinetic Models ◽  
Potential Energy Surfaces ◽  
Computational Investigation ◽  
Bottom Up ◽  
Energy Surfaces

Detailed kinetic models (DKMs) are the most fundamental “bottom-up” approaches to computational investigation of the pyrolysis and oxidation of fuels.

scholarly journals O(3P) + CO2 scattering cross-sections at superthermal collision energies for planetary aeronomy

2019 ◽  
Vol 491 (4) ◽  
pp. 5650-5659 ◽  
Author(s):  
Marko Gacesa ◽  
R J Lillis ◽  
K J Zahnle
Keyword(s):  
Cross Sections ◽  
Potential Energy Surfaces ◽  
Energy Transport ◽  
Basis Set ◽  
Planar Geometry ◽  
Rotational States ◽  
Mass Scaling ◽  
Linear Configuration ◽  
Energy Surfaces ◽  
Scattering Cross Sections

ABSTRACT We report new elastic and inelastic cross-sections for O(3P) + CO2 scattering at collision energies from 0.03 to 5 eV, of major importance to O escape from Mars, Venus, and CO2-rich atmospheres. The cross-sections were calculated from first principles using three newly constructed ab initio potential energy surfaces correlating to the lowest energy asymptote of the complex. The surfaces were restricted to a planar geometry with the CO2 molecule assumed to be in linear configuration fixed at equilibrium. Quantum-mechanical coupled-channel formalism with a large basis set was used to compute state-to-state integral and differential cross-sections for elastic and inelastic O(3P) + CO2 scattering between all pairs of rotational states of CO2 molecule. The elastic cross-sections are 35 per cent lower at 0.5 eV and more than 50 per cent lower at 4 + eV than values commonly used in studies of processes in upper and middle planetary atmospheres of Mars, Earth, Venus, and CO2-rich planets. Momentum transfer cross-sections, of interest for energy transport, were found to be proportionally lower than predicted by mass scaling.

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