Molecular beam studies of elementary reactions relevant in plasma/combustion chemistry: O(3P) + unsaturated hydrocarbons

The identification of the primary products and the determination of their branching ratios as a function of translational energy (temperature) for multi-channel elementary (bimolecular) reactions of importance in combustion flames and plasma-assisted combustion still represent a challenge for traditional kinetics experiments. On the other hand, this kind of information is central for the detailed modeling of combustion/plasma systems. In this short review, the significant contribution provided in this area by the crossed molecular beam (CMB) scattering method with “universal” mass-spectrometric detection and time-of-flight analysis is illustrated. In particular, we describe the basics of the CMB technique empowered with “soft” electron-impact ionization as recently implemented in our laboratory, and report on its application to the study of the multi-channel elementary reactions of ground state atomic oxygen, O(3P), with unsaturated hydrocarbons containing two carbon atoms (acetylene and ethylene), three carbon atoms (propyne, propene, and allene), and also four carbon atoms (1-butene, 1,2-butadiene, and 1,3-butadiene), which are of paramount interest in combustion flames and plasma-assisted combustion of hydrocarbons. These studies are usually complemented in a synergistic manner by high-level electronic structure calculations of the underlying potential energy surfaces and related statistical (and dynamical when feasible) calculations of product branching ratios. The complementarity to kinetics studies and the implications of the dynamics results for the modeling of combustion/plasma chemistry will be commented on.