MASS-SPECTROMETRIC AND THEORETICAL INVESTIGATIONS INTO THE FORMATION OF ARGON MOLECULAR-IONS IN PLASMA-MASS SPECTROMETRY

The abundance and distribution of argon molecular ions (e.g., ArH+, Ar O+, ArN+, Ar-2(+) and MAr(+); M = metal) in plasma MS (ICP-MS, LA-ICP- MS and rf-GDMS) were investigated and compared. In ICP-MS the non-meta l argon molecular ions were formed with higher intensity compared with the metal argide ions. This could be explained by theoretical calcula tions of the binding energies. The ArH+ ion can be viewed as an isoele ctronic system, comparable to HCl. The intensities of diatomic metal a rgide ions relative to metal ions in ICP-MS are less than 10(-4). A co rrelation between the intensities of metal argide ions with the bond d issociation energies of diatomic ions was found. The highest intensity of metal argide ions, of the order of per cent. values, were observed in rf-GDMS. The intensity of the argon molecular ions in an rf-GD var ied by up to three orders of magnitude as a function of the plasma par ameters (e.g., argon pressure in the GD ion source). The characteristi c distribution of diatomic argide ions of REEs in ICP-RIS was found to be comparable to the distribution of rare earth oxide ions.