Cluster formation processes in laser and spark plasmas of rare earth oxide–graphite mixtures

Abstract

The abundance distribution of cluster ions (C_n⁺, MC_n⁺ and MO⁺; M = rare earth element) of a rare earth oxide–graphite mixture in laser ionization mass spectrometry (LIMS) and spark source mass spectrometry (SSMS) was investigated. In LIMS and SSMS, a typical alternating abundance distribution for positively charged carbon and carbide cluster ions of rare earth elements was found. Clusters with an odd number of atoms were observed with a higher intensity in comparison with clusters with an even number of atoms. A maximum cluster formation rate of carbon clusters (C_n⁺) and metal carbide clusters (MC_n⁺) using a rare earth oxide–graphite mixture target was observed at a laser power density of about 10⁸ W cm^–2. The intensities of positively singly charged monoxide and dicarbide ions of rare earth elements correlate with the dissociation energy of the molecules, which depends directly on the transition energy from the 4f^n–15d6s² electronic state to the 4fⁿ6s² electronic state for rare earth elements. Additionally, measurements using high resolution inductively coupled plasma mass spectrometry (ICP-MS), have shown that the typical distribution of oxide ions of rare earth elements with increasing atomic number is comparable to that found in LIMS and SSMS.