Reactive scattering of atoms and radicals

Intersystem crossing and dynamics in O( 3 P) + C 2 H 4 multichannel reaction: Experiment validates theory

“…As described elsewhere (29), data analysis assumes a CM differential cross-section Iðθ; E 0 T Þ for each channel that is separable in the product of two parts: one depending only on the CM scattering angle, TðθÞ, and the other only on the product translational energy, PðE 0 T Þ (coupling between these two functions is weak under our experimental conditions). The total CM differential cross-section at a given m∕z is obtained by a weighted sum of the Iðθ; E 0 T Þ for the various channels contributing to the signal at that m∕z value.…”

“…We have recorded the angular and velocity distributions of the reaction products by a triply differentially pumped, ultrahigh-vacuum (10 −11 mbar) detector equipped with a tunable electron impact ionizer followed by a quadrupole mass filter and an off-axis electron multiplier (29)(30)(31). The whole detector unit can be rotated in the plane of the two beams around their intersection axis (Θ ¼ 0°represents the direction of the atomic oxygen beam).…”

“…The whole detector unit can be rotated in the plane of the two beams around their intersection axis (Θ ¼ 0°represents the direction of the atomic oxygen beam). The product angular distributions are measured by modulating (by a tuning fork chopper at 160 Hz) the ethylene beam for background subtraction; the velocity of reactants and products is derived using single-shot and pseudorandom, respectively, TOF analysis (29). For these experiments, a continuous supersonic beam of atomic oxygen was obtained by means of a radiofrequency (RF) discharge beam source (33), in which 200 mbar of a 5% O 2 ∕He gas mixture was discharged through a 0.28 mm diameter quartz nozzle at 300 W of RF power; peak velocity and speed ratio were 2;500 m∕s and 5.6, respectively.…”

Dynamics of chemical reactions of astrophysical interest

“…The effort to understand the behaviour of atom and small radical reactions is motivated by the great relevance they bear in many areas -from Earth's to planetary atmosphere chemistry, from combustion to interstellar cloud chemistry -in addition to their fundamental interest. Laboratory experiments suitable for investigating the dynamics of astrophysically important reactions have now become possible thanks to the development of laser photolysis (Patel-Misra & Dagdigian 1992, Che & Liu 1995, laser ablation (Kaiser et al 1995) and electrical discharge (Alagia et al 1995) techniques for generating radical beams.…”

“…In particular, semi-empirical and ab initio potential energy surfaces (PESs) have been developed and dynamical calculations, both classical and quantummechanical, have been carried out on them (see references in Alagia et al 1995 andCasavecchia et al 1995).…”