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

The first ionization potential of einsteinium (IPEs) was determined by resonance ionization mass spectroscopy (RIMS) using samples with less than or equal to 10(12) atoms of Es-254 (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 IPEs. 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)). (C) 1998 Elsevier Science S.A.