Machine Learned Potential Enables Molecular Dynamics Simulation to Predict the Experimental Branching Ratios in the NO Release Channel of Nitroaromatic Compounds.

This study employs a machine learning (ML) model using the Gaussian process regression algorithm to generate potential energy surfaces (PES) from density functional theory calculations, facilitating the investigation of photodissociation dynamics of nitroaromatic compounds, resulting in NO release. The experimentally observed trends in the slow-to-fast branching ratios of the NO moiety were captured by estimating the branching ratio between the two distinct reaction pathways, viz., roaming and oxaziridine mechanisms, calculated from molecular dynamics simulations performed on a reduced two-dimensional T surface.

Molecular Association and Reactivity of the Pyridine Dimer Cation.

A recent experimental report has identified the formation of the C-N hemibonded pyridine dimer cation following vacuum ultraviolet near-threshold photoionization [, , 12, 4936-4943]. Herein, the dynamics and consequent reactivity of the pyridine dimer cation were investigated employing Born-Oppenheimer molecular dynamics (BOMD) simulations. An antiparallel π-stacked pyridine dimer in the neutral ground state is transformed into a noncovalently interacting C-H···N hydrogen-bonded structure which can lead to proton transfer in the cationic state.

Probing the Role of Solvent Configurations and Local Electric Fields on HX (X = F, Cl, Br and I) Dissociation in Water Clusters.

The acidity of hydrohalic acids increases down the group, with HF and HI being the weakest and strongest acids. Electronic structure calculations suggest that the critical electric fields required for the dissociation of HF, HCl, HBr, and HI are 347, 193, 163, and 153 MV cm, respectively, which are proportional to their corresponding p values and emphasize that in these systems the bond dissociation energy determines the p. The solvent configuration plays a significant role in the acid dissociation process, which is illustrated by a particular configuration of three water molecules around HX and favors dissociation of only HBr, even though the critical electric field required for the dissociation of HI is lower than that of HBr, as depicted in the graphical abstract.

Mechanistic variances in NO release: isomers of nitrophenol and nitroaniline.

The NO release following 266 nm photolysis of and isomers of nitrophenol and nitroaniline shows a bimodal translational energy distribution, wherein the slow and fast components originate from dynamics in the S and T states, respectively. The translational energy distribution profiles for any NO product state show a higher slow-to-fast (s/f) branching ratio for the isomer in comparison with the isomer. The observed variation in the s/f branching ratio the and isomers is attributed to the presence of intramolecular hydrogen bonding between the substituent and NO moiety, which favours the roaming mechanism.

Dissociative Photoionization of Dimethylpyridines and Trimethylpyridine at 266 nm: Dynamics of Methyl Radical Release.

The 266 nm photolysis of various positional isomers of dimethylpyridines and trimethylpyridine was investigated by measuring the translational energy distribution of the methyl radical following {sp}C-C{sp} bond dissociation. The observed translational energy distribution is attributed to the dissociative photoionization in the cationic ground state following [1 + 1 + 1] three-photon absorption. The translational energy distribution profiles of the methyl radical were broad with the maximum translation energy in excess of 2 eV, which originates due to the dissociation of {sp}C-C{sp} bond ortho to the N atom in the ring.