Cross Sections for Electron-Impact Fragmentation and Dissociation Energies of the Dimer and Tetramer of Bismuth

Abstract

Although molecules of bismuth have been the subject of numerous studies, the investigation reported here represents the first reliable mass‐spectrometric study of these molecules. First of all, this article describes a new method for handling the problem of apportionment of ion currents in mass‐spectrometric analyses when both direct ionization and electron‐impact fragmentation contribute comparable currents to a specific ion species. The study of the molecules Bi and Bi₂ provides an experimental test of this apportionment method for the ion current of Bi⁺. Second, this article describes measurements of the heats of dissociation and atomization of Bi₄. The results of these measurements provide the only reliable information now available on this molecule. The experimental heat of atomization of Bi₄ at 298°K is found to be 139.7±1.9 kcal mole⁻¹. Other thermodynamic data obtained for the dimer and monomer confirm the results of previous investigators.