A theoretical study of the isotope selective excitation of 138La from 2D?,? states

Abstract

Isotope ratio enhancement factors and isotopic selectivities for 138La in a natural abundance lanthanum sample as well as an enriched sample have been computed theoretically for the 5d6s2 2D32-5d26p 2F520 (593.068 nm), 5d6s2 2D52-5d26p 2F720 (593.062 nm), 5d6s2 2D32-5d26p 2D320 (550.134 nm), 5d6s2 2D52-5d26p 2D520 (545.514 nm) and 5d6s2 2D32-5d6s6p 4F320 (753.923 nm) transitions for a narrow band laser excitation in a one-photon resonant two-photon ionisation scheme considering a Lorentzian atomic profile for simulation of the excitation spectrum. Simulations have been carried out for a laser bandwidth of 50 MHz. The coherence effects are ignored in the computation as the laser bandwidth (50 MHz) is much smaller than the largest separation between the hyperfine levels (i.e. γL ⪡ ΔHFS). The results obtained for the 2D32-4F320 (753.923 nm) transition are in excellent agreement with the experimental results obtained by Young et al. using diode laser initiated resonance ionisation mass spectrometry. The isotopic selectivities and isotope ratio enhancement factors computed for the 2D52-2D520 (545.514 nm) transition are about 19% higher than the 2D32-4F320 (753.923 nm) transition used by Young et al. This increased isotopic selectivity can be used for isotope selective excitation of 138La with improved detection sensitivity. This method demonstrates its usefulness in identifying the most efficient atomic lines in order to focus experimental effort on these transitions.