Mass Spectrometric Studies of Atom–Molecule Reactions Using High-Intensity Crossed Molecular Beams

Abstract

Elementary gas phase reactions have been studied with high‐intensity crossed molecular beams. A detailed analysis is presented on the sensitivity factors involved in mass spectrometric detection of free radicals formed in ordinary chemical reactions as contrasted to surface ionization detection of the products of alkali atom reactions. Free radicals have been observed in a number of atom–molecule reactions, including: (1) Cl atoms with n‐butane and isobutane, (2) H atoms with NO₂ and hydrazine, and (3) O atoms with hydrazine, monomethylhydrazine, and 1,1‐dimethylhydrazine. The O atom reactions with the hydrazines are very interesting because of the marked proclivity for an O atom to abstract two H atoms from opposite ends of the molecule, forming diimide (HNNH) in the case of hydrazine and methyldiazene (HNNCH₃) in the case of monomethylhydrazine. Ionization potentials of the free radicals and unstable molecules produced in the reactions have been measured and used in conjunction with appearance potentials of the corresponding ions to calculate relevant molecular and radical bond dissociation energies and heats of formation.