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Theoretical Study on the Formation of H‐ and O‐Atoms, HONO, OH, NO, and NO 2 from the Lowest Lying Singlet and Triplet States in Ortho ‐Nitrophenol Photolysis
Author(s) -
Vereecken L.,
Chakravarty H. K.,
Bohn B.,
Lelieveld J.
Publication year - 2016
Publication title -
international journal of chemical kinetics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.341
H-Index - 68
eISSN - 1097-4601
pISSN - 0538-8066
DOI - 10.1002/kin.21033
Subject(s) - intersystem crossing , chemistry , photodissociation , singlet state , dissociation (chemistry) , photochemistry , triplet state , ground state , excited state , radical , isomerization , singlet fission , atomic physics , molecule , catalysis , physics , biochemistry , organic chemistry
The photolysis of nitrophenols was proposed as a source of reactive radicals and NO x compounds in polluted air. The S 0 singlet ground state and T 1 first excited triplet state of nitrophenol were investigated to assess the energy dependence of the photofragmentation product distribution as a function of the reaction conditions, based on quantum chemical calculations at the G3SX//M06–2X/aug‐cc‐pVTZ level of theory combined with RRKM master equation calculations. On both potential energy surfaces, we find rapid isomerization with the aci ‐nitrophenol isomer, as well as pathways forming NO, NO 2 , OH, HONO, and H‐, and O‐atoms, extending earlier studies on the T 1 state and in agreement with available work on other nitroaromatics. We find that accessing the lowest photofragmentation channel from the S 0 ground state requires only 268 kJ/mol of activation energy, but at a pressure of 1 atm collisional energy loss dominates such that significant fragmentation only occurs at internal energies exceeding 550 kJ/mol, making this surface unimportant for atmospheric photolysis. Intersystem crossing to the T 1 triplet state leads more readily to fragmentation, with dissociation occurring at energies of ∼450 kJ/mol above the singlet ground state even at 1 atm. The main product is found to be OH + nitrosophenoxy, followed by formation of hydroxyphenoxy + NO and phenyloxyl + HONO. The predictions are compared against available experimental data.