OH produced from o-nitrophenol photolysis: A combined experimental and theoretical investigation

Abstract

Photodissociation dynamics of o-nitrophenol in the gas phase at different photolysis wavelengths (361-390 nm) is investigated, and the nascent OH radical is observed by the single-photon laser-induced fluorescence technique. At all the photolysis wavelengths, the OH radicals are formed in vibrationally cold state (upsilon(")=0) and have similar rotational state distributions. The average rotational temperature for all the photolysis wavelengths is approximately 970+/-120 K, corresponding to a rotational energy of 1.9+/-0.2 kcal mol(-1). The spin orbit and Lambda-doublet states of the OH fragments formed in the dissociation are measured to have nonstatistical distributions. To get an insight into the dissociative mechanism leading to OH formation in the photolysis of o-nitrophenol, the potential energy surfaces of the OH-forming channels are mapped by ab initio theoretical calculations. According to both experimental and theoretical results, a possible mechanism for OH formation is proposed.

Intersystem crossing-branched excited-state intramolecular proton transfer for o-nitrophenol: An ab initio on-the-fly nonadiabatic molecular dynamic simulation

“…The present trajectory simulation indicates that the aci-nitro isomers are mostly generated on the triplet states, especially on T 1 state and this confirms the previous assumption in which the HONO split-off motion is taken place in the triplet manifold 29 61 62 . The present simulation also indicates that the o-NP dynamic decay via ISC ESIPT is mostly in time scale of subpicosecond (expect tunneling ESIPT) and this is in close agreement with the observations for a large number of nitrated polycyclic aromatic compounds 63 64 65 .…”

Theoretical Study on the Formation of H- and O-Atoms, HONO, OH, NO, and NO2from the Lowest Lying Singlet and Triplet States inOrtho-Nitrophenol Photolysis

“…Since the first observation of HONO formation from ortho ‐nitrophenol by Bejan et al a decade ago, the photolysis of ortho ‐nitrophenol is known to be a source of OH radicals and HONO . This process was thought to contribute to the concentrations of HONO observed in the troposphere, which were well beyond what was supported by the known HONO sources as implemented in atmospheric models .…”

The community atmospheric chemistry box model CAABA/MECCA-4.0

“…The enhancement is applied to the photolysis rate coefficients (j values) of nitrooxyacetone (NOA), nitrooxyacetaldehyde (NO3CH2CHO), lumped nitrates of methyl ethyl ketone (LMEKNO3), nitrates of MVK (methyl vinyl ketone) and MACR, and unsaturated C 5nitrooxyaldehyde from the isoprene + NO 3 reaction. Keto-enol tautomerization of aldehydes induced by light absorption is implemented based on data for acetaldehyde (Clubb et al, 2012). The enols are in equilibrium with the corresponding aldehydes by HCOOH catalysis (da Silva, 2010).…”

“…Nitrophenols undergo photolysis yielding HONO, according to Bejan et al (2006) and Chen et al (2011), and assumed co-products being cyclic ketenes. However, the OHformation channel (Cheng et al, 2009;Vereecken et al, 2016) is not implemented.…”