Molecular Beam Analyzer for Identifying Transient Intermediates in Gaseous Reactions

摘要

When using a mass spectrometer to monitor free radical and atom intermediates in rapid gas-phase reactions, identification of the parent species of each ion is made difficult by fragmentation processes that occur at electron energies necessary for optimum ionization cross sections. Molecular beam analysis is a new approach to this problem whereby molecular beam measurements are used to characterize neutral species before they are ionized. Thus, the trajectory of a particle in an inhomogeneous magnetic field shows whether or not it has a large magnetic moment characteristic of a free radical, its motion in an inhomogeneous electric field indicates its symmetry and the magnitude of its electric dipole moment, and its velocity distribution determines its mass when the source temperature is known. Using these techniques, various atom, free radical and unstable molecular species have been identified in gases excited by microwave discharge or as products of atom-molecule reactions. (Author)