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RESEARCH PRODUCT

Determination of the first ionization potential of einsteinium by resonance ionization mass spectroscopy (RIMS)

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Abstract The first ionization potential of einsteinium (IP Es ) was determined by resonance ionization mass spectroscopy (RIMS) using samples with ≤10 12 atoms of 254 Es ( T 1/2 =276 days). This method is based on the measurement of photoionization thresholds as a function of applied electric field strength, followed by extrapolation to zero field strength to yield IP Es . An atomic beam of Es was created by heating a filament on which einsteinium was electrodeposited from an aqueous solution onto a tantalum backing and covered with titanium metal. Es atoms were ionized via a three-step excitation scheme, and the ions mass-selectively detected in a time-of-flight (TOF) mass spectrometer. The excitation scheme used included a previously unknown EsI level at 32 924.9 cm −1 . Furthermore, an autoionizing state at 51 447.3 cm −1 was also found. The first ionization potential of Es was determined to be 6.3676(5) eV (≡51 358(5) cm −1 ).