Collisions between methyl peroxy radicals do not react in the triplet excited state, and lead to tetroxide formation in the singlet ground state.

The lifetimes of pre-reactive complexes, although implicitly part of the equations used to model many gas-phase bimolecular reactions, have seldom been included in quantitative calculations of rate coefficients. Here, we demonstrate the application of empirical molecular dynamics simulations of collisions between peroxy radicals to model association lifetimes. With the exception of the methyl peroxy−acetyl peroxy system, measurements of the lifetimes based on a phenomenological model are shown to correlate well with available experimental data for recombination reactions of peroxy radicals in cases where the ratelimiting transition state lies below the reactants in energy. Further, we predict reaction rates for larger α-pinene-derived peroxy radicals, and we interpret our results in tandem with available experimental data on these systems, which are of great relevance to improve our understanding of atmospheric aerosol formation.

In the presence of a halide ion, hypohalous acids can adopt two binding motifs upon formation of the ion–molecule complexes [XHOY]− (X, Y = Cl, Br, I): a hydrogen (HB) bond to the acid OH group and a halogen (XB) bond between the anion and the acid halogen. Here we isolate the X-bonded Cl–·IOH ion–molecule complex by collisions of I–·(H2O) n clusters with HOCl vapor and measure its vibrational spectrum by IR photodissociation of the H2-tagged complex. Anharmonic analysis of its vibrational band pattern reveals that formation of the XB complex results in dramatic lowering of the HOI bending fundamental frequency and elongation of the O–I bond (by 168 cm–1 and 0.13 Å, respectively, relative to isolated HOI). The frequency of the O–I stretch (estimated 436 cm–1) is also encoded in the spectrum by the weak v = 0 → 2 overtone transition at 872 cm–1.

There is much current interest in materials that are made entirely or mostly of nitrogen atoms. Such materials, polynitrogens, may reveal new aspects of nitrogen chemistry, and are believed to provide a possible basis for novel energetic substances. An interesting family of such materials, in which the N 5 + group appears as a cation, was prepared by K. O. Christe and co-workers. Little is known as yet on the microscopic properties of these materials. In this paper, we report theoretical calculations to predict the structure, energetic stability and decomposition dynamics of the polynitrogen molecule N 5 + B(N 3 ) 4 − , the building block of a solid prepared by Christe, and of the dimer of this molecule. The structures are computed at the B3LYP-D3 level of DFT. ab initio molecular dynamics simulations are used to explore the thermal stability of the species and the decomposition mechanism. It is found that the N 5 + B(N 3 ) 4− ion-pair decomposes on a picosecond time scale at T = 200 K, with an ultrafast release of four N 2 molecules, which is very exothermic. The species B(N 3 ) 3 is a product. The dimer is considerably more stable. Sensitivity of the process to temperature and to an applied force is reported. Possible applications of this material are briefly discussed.

Molecular dynamics simulations using directly ab initio potentials are carried out for the ionically bonded clusters [(Cl)(HO)] and [(F)(HO)] to explore their transitions to the hydrogen-bonded [(HCl)(HO)] and [(HF)(HO)] structures during the first picosecond of simulation. Both the ionic and the H-bonded structures that are formed are highly symmetric. It is found that proton transfers are concerted in all trajectories for [(Cl)(HO)]. For [(F)(HO)], the fully concerted mechanism is dominant but partially concerted transfers of two or three protons at the same time also occur. The concerted mechanism also holds for the reverse process of ionization of neutral acid molecules. It is suggested that the high symmetry of the ionic and the H-bonded structures plays a role in the preference for concerted transfers. Possible implications of the results for proton transfers in other systems are discussed.