Kinetic origin of the ozone isotope effect: a critical analysis of enrichments and rate coefficients

Dynamics of the O-Atom Exchange Reaction 16O(3P) + 18O18O(3Σg–) → 16O18O(3Σg–) + 18O(3P) at Hyperthermal Energies

“…Inelastic Collisions. In the experiments, the lab frame TOF and angular distributions of the inelastically scattered 16 O atoms were measured. In the QCT calculations, a collision was The fact that the lab-frame predictions, calculated from the best-fit experimental and the QCT c.m.…”

“…[10][11][12] _ENREF_13_ENREF_16 Numerous explanations for the unexpected enrichment have been offered in the literature since then. Isotope-dependent rates of ozone formation and the competing atom exchange reactions have been measured, [13][14][15][16] and the small change in reaction exoergicity due to the difference in zero-point energies of different isotopologues was proposed as a possible explanation for the unexpected isotope enrichment. However, zero-point energy effects may not be sufficient to alter ozone kinetics significantly, 16 leading to the conclusion that the isotope effect is dynamically driven.…”

“…Isotope-dependent rates of ozone formation and the competing atom exchange reactions have been measured, [13][14][15][16] and the small change in reaction exoergicity due to the difference in zero-point energies of different isotopologues was proposed as a possible explanation for the unexpected isotope enrichment. However, zero-point energy effects may not be sufficient to alter ozone kinetics significantly, 16 leading to the conclusion that the isotope effect is dynamically driven. [17][18][19][20][21] It seems clear that the dynamics of both the bimolecular step and the collisional stabilization of the transient O 3 complex are important.…”

“…translational energy distribution showed a maximum close to the available energy (E avl ), suggesting relatively little rotational and vibrational excitation in the products. The rotational distribution of product 16 23 based on the earlier work of Siebert, Schinke, and Bittererova. 24 This PES for the O + O 2 system is characterized by a deep well corresponding to O 3 , with a submerged potential barrier ("reef") in the O + O 2 entrance/exit channel, now thought to be an artifact.…”

“…At impact parameters above 2.1 Å, the 16 O atom is reflected from the outer repulsive wall of the O 2 molecule, resulting in exclusively forward scattering, while collisions at impact parameters below ~2 Å access the O 3 potential well and lead to ejection of either an 16 O or an 18 O atom. Scattering remains preferentially forward in both cases due to the large momentum of the attacking 16 O atom.…”