Double-resonance measurements of isotope shifts and hyperfine structure in Gd I with hyperfine-state selection in an intermediate level

Abstract

Isotope shifts and hyperfine structure have been measured in the 4f7 5d6s2 9D6 -- X9 D6 (;38 024. 9 cm-1) transition in atomic gadolinium using high- resolution resonance ionization mass spectroscopy. Excitation was performed as a resonance-enhanced two-photon transition with the 4f7 5d6s6p 9F7 state as an intermediate level. Selective population of hyperfine states in the first excitation step allowed assignment of all transitions in the complex hyperfine spectrum of the odd isotopes 155,157Gd and evaluation of the magnetic dipole and electric quadrupole hyperfine structure constants for the X 9D6 state. Measured values for the isotope shifts of all stable Gd isotopes have been used to derive specific mass shift and field shift factors. The obtained spectroscopic information leads to the conclusion that the X 9D6 state is a 4f75d6s8s configuration.