Welcome
December 07, 2018
First Ionization Potentials of Fm, Md, No, and Lr:
Verification of Filling-Up of 5f Electrons and Confirmation of the Actinide Series
In a current paper in the Journal of the American Chemical Society (JACS), we report the first ionization potentials (IP1) of the heavy actinides, fermium (Fm, atomic number Z = 100), mendelevium (Md, Z = 101), nobelium (No, Z = 102), and lawrencium (Lr, Z = 103).
Current Periodic Table. The position of the studied elements at the end of the actinide series is highlighted. © B. Schausten, GSI |
The surface ion source: grey tantalum tube in the image center, surrounded by two heating filaments. It is installed at JAEA Tokai, Japan © JAEA |
The first ionization potential (IP1) is the energy required to remove the most weakly bound electron from
a neutral atom and is a fundamental property of any chemical element.
The IP1 values were determined in an atom-at-a-time regime using a method based on a surface ionization process
in a tantalum ionizer, coupled to an online mass separation technique.
The efficiency of the surface ionization process depend directly on the IP1.
The measured IP1 values agree well with those predicted by state-of-the-art relativistic calculations
performed alongside the present measurements. The value measured for No also agrees well with the
laser spectroscopic work carried out at GSI
in the group of Prof. Michael Block.
Similar to the well-established behavior for the lanthanides, the (IP1)values of the heavy actinides up to No
increase with filling up the 5f orbital, while that of Lr is the lowest among the actinides.
These results clearly demonstrate that the 5f orbital is fully filled at No with the
[Rn]5f147s2
configuration
and that Lr has a weakly bound electron outside the No core. In analogy to the lanthanide series,
the present results unequivocally verify that the actinide series ends with Lr.
The experiment led by our
collaborators at JAEA Tokai, Japan,
where it was carried out at the JAEA Tandem accelerator,
in collaboration with international partners including experimenters from our group.