Universal crossed beam imaging studies of polyatomic reaction dynamics

Crossed-beam imaging studies of polyatomic reactions show surprising dynamics not anticipated by extrapolation from smaller model systems.

Primary vs. secondary H-atom abstraction in the Cl-atom reaction with n-pentane

Velocity map imaging (VMI) measurements and quasi-classical trajectory (QCT) calculations on a newly developed, global potential energy surface (PES) combine to reveal the detailed mechanisms of reaction of Cl atoms with n-pentane. Images of the HCl (v = 0, J = 1, 2 and 3) products of reaction at a mean collision energy of 33.5 kJ mol^-1 determine the centre-of-mass frame angular scattering and kinetic energy release distributions. The HCl products form with relative populations of J = 0-5 levels that fit to a rotational temperature of 138 ± 13 K. Product kinetic energy release distributions agree well with those derived from a previous VMI study of the pentyl radical co-product [Estillore et al., J. Chem. Phys. 2010, 132, 164313], but the angular distributions show more pronounced forward scattering. The QCT calculations reproduce many of the experimental observations, and allow comparison of the site-specific dynamics of abstraction of primary and secondary H-atoms. They also quantify the relative reactivity towards Cl atoms of the three different H-atom environments in n-pentane.

Crossed-beam DC slice imaging of fluorine atom reactions with linear alkanes

We report the reaction dynamics of F atom with selected alkanes studied by crossed beam scattering with DC slice ion imaging. The target alkanes are propane, n-butane, and n-pentane. The product alkyl radicals are probed by 157 nm single photon ionization following reaction at a collision energy of ∼10 kcal mol(-1). The analyzed data are compared with the corresponding theoretical studies. Reduced translational energy distributions for each system show similar trends with little of the reaction exoergicity appearing in translation. However, the pentane reaction shows a somewhat smaller fraction of available energy in translation than the other two, suggesting greater energy channeled into pentyl internal degrees of freedom. The center-of-mass angular distributions all show backscattering as well as sharp forward scattering that decreases in relative intensity with the size of the molecule. Possible reasons for these trends are discussed.