Periodic Table of the Elements

The elements in this periodic table are color-coded to depict how Resonance Ionization would be applied to each element. See the description below the chart.

Preferred Three-Color Scheme - Analysis for these elements utilizes two one-photon resonance transitions, followed by a one-photon photoionization step. This method gives the greatest sensitivity (ppb and better).

Two-Photon Transition Required - The first excited state in these elements is too high to reach with standard frequency doubling and mixing techniques in crystals. Therefore, a simultaneous two-photon excitation is used. This requires much higher laser intensity than does the Preferred Three Color Scheme. This higher intensity produces multiphoton ionization interferences (poorer discrimination) and the focussing used to achieve the higher intensity causes poorer spatial overlap (poorer sensitivity, on the order of ppm). However, this method is still better than nonresonant ionization or SIMS in almost all cases.

Vacuum UV Required - For fluorine, the first excited state is too high even for two-photon excitation using standard frequency doubling and mixing techniques in crystals. For this element, a four-wave mixing method can be used to achieve vacuum ultraviolet wavelengths necessary for a one-photon excitation. This method has also been used for argon, although a two-photon excitation is feasible for argon. The four-wave mixing technique is possible for all the elements designated as requiring two-photon transitions. Even though the four-wave mixing technique will frequently give better discrimination and detection limits than two-photon excitation, it is more complex and most expensive, and therefore seldom used.

Presently Not Practical - Helium and neon are not practical elements for resonance ionization from the ground state. Ironically, helium was the first element used to demonstrate resonance ionization, but that early work at Oak Ridge National Laboratory was performed on excited metastable helium.

Performed at Atom Sciences - Atom Sciences, Inc. has performed analyses for elements marked with a navy blue "A".

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Last Modified Aug 25, 2008