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Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NOx

Automated, High-resolution Mobile Collection System for the Nitrogen Isotopic Analysis of NO_x

Published on: December 20, 2016

Primer estudio de principios sobre el papel de la interconversión entre NO2, N2O4, cis-ONO-NO2 y trans-ONO-NO2 en los

Wei-Guang Liu¹, William A Goddard

¹Materials and Process Simulation Center, California Institute of Technology , Pasadena, California 91125, United States.

Journal of the American Chemical Society

|July 12, 2012

Resumen

Los estudios de mecánica cuántica revelan distintas vías para la formación de dímeros de dióxido de nitrógeno (NO2), aclarando la hidrólisis de NO2 y las reacciones hipergólicas. La formación simétrica de dímeros N2O4 no tiene barreras, mientras que los isómeros cis y trans tienen diferentes barreras de energía.

Área de la Ciencia:

Química computacional es la química computacional.
Química física es la química física de las cosas.
La cinética de las sustancias químicas.

Sus antecedentes:

Las observaciones experimentales de la hidrólisis y la hipergolicidad del NO2 sugieren la participación del dímero del NO2.
Comprender las estructuras de dímeros de NO2 (N2O4 simétrico, cis-ONO-NO2, trans-ONO-NO2) es crucial, pero complicado por la energía de resonancia del NO2.
Los métodos mecánicos cuánticos estándar muestran limitaciones para describir con precisión estos sistemas.

Objetivo del estudio:

Investigar las barreras energéticas y las vías para la formación de diferentes isómeros de dímeros de NO2.
Para comparar la fiabilidad de varios métodos mecánicos cuánticos para el estudio de estos sistemas.
Para aclarar los mecanismos detrás de la hidrólisis de NO2 y el intercambio de oxígeno isotópico.

Principales métodos:

Teoría funcional de la densidad (DFT) utilizando B3LYP funcional.
Métodos ab initio que incluyen MP2, CCSD (T) y GVB-RCI.
Cálculos de alto nivel a nivel RCCSD (T) /CBS para una determinación precisa de la barrera energética.

Principales resultados:

Las barreras entálpicas para la formación de dímeros: cis-ONO-NO2 (1,9 kcal/mol) y trans-ONO-NO2 (13,2 kcal/mol) en RCCSD(T) /CBS.
GVB-RCI indica que no hay barreras para la formación simétrica de N2O4, en contraste con las barreras no físicas de RCCSD (T).
La isomerización de N2O4 a trans-ONO-NO2 tiene una barrera alta (43,9 kcal/mol), lo que lo excluye para la hidrólisis de NO2; la formación a través de cis-ONO-NO2 es más favorable (barrera de 2,4 kcal/mol).

Conclusiones:

La elección del método mecánico cuántico tiene un impacto significativo en las barreras de energía calculadas para la formación de dímeros de NO2.
La formación de N2O4 simétrico es energéticamente fácil, mientras que las isomerizaciones implican barreras sustanciales.
Un mecanismo propuesto para el intercambio de oxígeno isotópico en el NO2 implica la formación de trans-ONO-NO2 y la migración ON+.

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