Abstract

Resonance ionization mass spectrometry (RIMS) is the technique of resonance ionization spectroscopy (RIS) followed by mass spectrometry. By means of RIS, the isobaric interference of mass spectrometry is removed. Therefore RIMS is applied to a lot of analytical problems such as determination of isotope ratio, trace analysis and so on. It has been, however, shown experimentally and theoretically that there are considerable differences of ionization probability between even and odd isotopes although all isotopes are excited by the laser whose bandwidth is large enough to overlap their hyperfine levels.^[1,2] Methods to eliminate biases due to hyperfine structure are supposed for the determination of isotope ratio.^[3] It is needed for the precise determination of the isotope ratio that responses of even- and odd-mass isotopes should be understood. We have experimentally investigated these differences dependent on the laser intensity on various conditions such as exciting scheme, polarization and electric field.

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