Exploring mechanisms of a tropospheric archetype: CH3O2 + NO

Abstract

Methylperoxy radical (CH3O2) and nitric oxide (NO) contribute to the propagation of photochemical smog in the troposphere via the production of methoxy radical (CH3O) and nitrogen dioxide (NO2). This reaction system also furnishes trace quantities of methyl nitrate (CH3ONO2), a sink for reactive NOx species. Here, the CH3O2 + NO reaction is examined with highly reliable coupled-cluster methods. Specifically, equilibrium geometries for the reactants, products, intermediates, and transition states of the ground-state potential energy surface are characterized. Relative reaction enthalpies at 0 K (ΔH0K) are reported; these values are comprised of electronic energies extrapolated to the complete basis set limit of CCSDT(Q) and zero-point vibrational energies computed at CCSD(T)/cc-pVTZ. A two-part mechanism involving CH3O and NO2 production followed by radical recombination to CH3ONO2 is determined to be the primary channel for formation of CH3ONO2 under tropospheric conditions. Constrained optimizations of the reaction paths at CCSD(T)/cc-pVTZ suggest that the homolytic bond dissociations involved in this reaction path are barrierless.

Global exploration of isomers and isomerization channels on the quantum chemical potential energy surface of H3CNO3

“…The present study not only entirely reproduced the reported isomeric‐conversion and DCs around HOCH 2 NO 2 but also disclosed many other conformers and reaction channels at the levels of B3LYP/6‐31G(d) and B3LYP/6‐311++G(d,p). Related to the chemistry of the atmosphere, many studies were made for methyl nitrate 21 and methylperoxy nitrite 31 , but the isomeric forms and isomerization channels reported were essentially the same as the present study, although some DCs not treated in the present study were shown for radical‐pair processes . A similar result to this study was reported for an isomerization channel between methyl nitrate 21 and methoxy dioxaziridine 45 in connection with the reaction of triplet nitrenes with oxygen .…”

“…As for isomerization routes at high energy regions, rigorous treatments need to be made for deeper understanding. Radical‐pair channels including CH 3 O + NO 2 have been studied in connection with methyl nitrate 21 and methyl peroxynitrite 31 . In some special cases, multi‐reference treatments as well as excited‐surface treatments including conical intersections and seams should also be taken into account.…”

“…This article describes a study on the exploration of isomers, isomerization reactions, as well as their reaction routes for H 3 CNO 3 using SHS‐ADDF. Studies on H 3 CNO 3 were reported recently in relation to combustion and atmospheric chemistry . The reaction channels for some isomers of H 3 CNO 3 including nitromethanol (HOCH 2 NO 2 ) and nitrosooxymethnol (HOCH 2 ONO) were elucidated using hybrid density‐functional‐theory (DFT) B3LYP method in connection with radical‐molecule reaction of CH 2 OH with NO 2 .…”

“…The reaction channels for some isomers of H 3 CNO 3 including nitromethanol (HOCH 2 NO 2 ) and nitrosooxymethnol (HOCH 2 ONO) were elucidated using hybrid density‐functional‐theory (DFT) B3LYP method in connection with radical‐molecule reaction of CH 2 OH with NO 2 . The reaction channels involving methyl nitrate (H 3 CONO 2 ) and methyl peroxynitrite (H 3 COONO) related to atmospheric systems were studied in different levels of calculations . We assumed that interesting chemistry would be discovered more from the GRRM for H 3 CNO 3 because of its potential of the formation of various functional groups, including OH, OO, OOH, OOO, CO, CHO, COOH, COOOH, CN, NH, NH 2 , NO, NO 2 , NO 3 , NOO, ONO, NOH, NOOH, NHOH, CH, CH 2 , and CH 3 , which can compose various chemical structures.…”

High performance global exploration of isomers and isomerization channels on quantum chemical potential energy surface of H5C2NO2

“…To get those species, unrestricted methods should be employed. Atmospheric species such as methyl nitrate and methylperoxy nitrite [45][46][47] and roaming channels involving distant radical pairs [11][12][13] should be treated by an unrestricted approach, such as UB3LYP levels.…”