Search

Reactive scattering of Cl atoms with C2H5I molecules has been studied over the range of initial translational energy E = 63 - 24 kJ mol-1, using a supersonic beam of Cl atoms seeded in He and Ne buffer gas. Laboratory angular and velocity distributions of ICl product were measured which show that reaction proceeds via a long-lived collision complex at low initial translational energy. However at intermediate and higher initial translational energy, a forward scattered component emerges with a higher product translational energy than that of the long-lived complex component. This breakdown of long-lived complex dynamics occurs more readily in collisions at large impact parameters in contrast to the osculating complex model which assumes a statistical distribution of lifetimes independent of impact parameter.

Reactive scattering of Cl atoms with CH3I molecules has been studied over the range of initial translational energy E = 62-23 kJ mol-1, using a supersonic beam of Cl atoms seeded in He and Ne buffer gas. Laboratory angular and velocity distributions of ICl product were measured which indicate that reaction occurs via a long-lived collision complex with forward scattering appearing only at the highest collision energy. The dependence of the total reaction cross section on initial translational energy was also determined. The observed reactive scattering arises from an endoergic dissociation of the collision complex. The results are interpreted by a model which accounts for the effect of angular momentum conservation on this endoergic dissociation compared with the favoured dissociation of the complex back to reactants.

Reactive scattering of O atoms with ICl molecules has been studied at an initial translational energy E = 40 kJ mol-1 using a supersonic beam of O atoms seeded in He and at E = 15 kJ mol-1 using O atoms seeded in Ne. Velocity distributions of OI product were measured by cross-correlation time-of-flight analysis. Full contour maps of the differential reaction cross-section have been obtained which show peaking almost equally in the forward and backward directions at both initial translational energies. The product translational energy distributions are consistent with a long-lived O-I-Cl collision complex dissociating via a loose transition state. The stability of the O-I-Cl complex is attributed to the low electronegativity of the central I atom compared with the peripheral atoms. This electronegativity ordering rule also determines the stability of the intermediates in the other reactions of oxygen atoms with halogen molecules. The mild peaking of the product angular distributions for O + ICl and IBr indicates that collision complexes have quite modest collision angular momenta L ∼ 40 ħ corresponding to impact parameters b ∼ 1·4 Å and that the angular momentum of the OI molecule in the loose transition state may be approximately half the product orbital angular momentum.

Reactive scattering of CH3 radicals with ICl, IBr, I2 and Br2 molecules has been studied at an initial translational energy E ∼ 30kJ mol-1, using a supersonic beam of CH3 radicals seeded in He buffer gas. Laboratory angular and velocity distributions of CH3I and CH3Br product have been measured which show a gradation from short-lived complex dynamics for ICl to rebound dynamics for I2 and Br2 with intermediate behaviour for IBr. This variation in dynamics is attributed to the form of the potential energy surface which shifts from a shallow hollow for CH3 + ICl to repulsion in the exit valley for CH3 + I2, Br2, with both features being present for the intermediate case of CH3 + IBr.

Reactive scattering of Cl atoms with C3H7I molecules has been studied over the range of initial translational energy E = 46-25 kJ mol-1, using a supersonic beam of Cl atoms seeded in He and Ne buffer gas. Laboratory angular and velocity distributions of ICl product were measured which show reaction proceeding via a long-lived collision complex at low initial translational energy. However a forward scattered component with a higher product translational energy appears at intermediate and higher initial translational energy. The decreased lifetimes for complexes formed in large impact parameter collisions and the high product translational energies reflect the reduced density of vibrational states prevailing for complexes with large values of the total angular momentum J ≲ 300 ħ.

Reactive scattering of Cl atoms with C3F7I molecules has been studied at an initial translational energy E = 47 kJ mol-1, using a supersonic beam of Cl atoms seeded in He buffer gas. Laboratory angular and velocity distributions of ICl product have been measured which show reaction proceeding via a long-lived collision complex. The forward and backward scattering has a higher product translational energy than the sideways scattering, with the intensity and energy of the forward scattering somewhat higher than the backward scattering. Long-lived collision dynamics first break down in collisions at large impact parameters with apparently incomplete energy transfer to internal modes of the C3F7 radical.