New Resonance Ionization Mass Spectrometry Scheme for Improved Uranium Analysis.

Resonance ionization mass spectrometry (RIMS) combines tunable laser spectroscopy with mass spectrometry to provide a high-efficiency means of analyzing solid materials. We previously showed a very high useful yield of 24% for analysis of uranium using three lasers to excite and ionize atoms sputtered from metallic uranium and uranium dioxide. A new resonance ionization scheme using only two lasers achieves a higher useful yield of 38% by accessing both the ground electronic state and a low-lying electronic state of atomic uranium that is significantly populated by sputtering.

High Useful Yield and Isotopic Analysis of Uranium by Resonance Ionization Mass Spectrometry.

Useful yields from resonance ionization mass spectrometry can be extremely high compared to other mass spectrometry techniques, but uranium analysis shows strong matrix effects arising from the tendency of uranium to form strongly bound oxide molecules that do not dissociate appreciably on energetic ion bombardment. We demonstrate a useful yield of 24% for metallic uranium. Modeling the laser ionization and ion transmission processes shows that the high useful yield is attributable to a high ion fraction achieved by resonance ionization.

Near infrared (NIR) strong field ionization and imaging of C₆₀ sputtered molecules: overcoming matrix effects and improving sensitivity.

Strong field ionization (SFI) was applied for the secondary neutral mass spectrometry (SNMS) of patterned rubrene films, mouse brain sections, and Botryococcus braunii algal cell colonies. Molecular ions of rubrene, cholesterol, C31 diene/triene, and three wax monoesters were detected, representing some of the largest organic molecules ever ionized intact by a laser post-ionization experiment. In rubrene, the SFI SNMS molecular ion signal was ~4 times higher than in the corresponding secondary-ion mass spectroscopy (SIMS) analysis.

Formation of neutral In(m)C(n) clusters under C60 ion bombardment of indium.

The formation of neutral gas phase indium carbide clusters under C60(+) ion bombardment of solid indium was investigated using laser based postionization prior to mass spectrometric detection. Two different postionization methods were used and shown to provide saturated photoionization efficiency, thereby delivering nearly the same information about the composition of the sputtered material. The resulting size distributions of neutral In(m)C(n) clusters are compared with those of the corresponding cationic secondary cluster ions and discussed in terms of calculated cluster properties.