Isotope shifts and hyperfine structure of the Fe I 372 nm resonance line

Abstract

We report measurements of the isotope shifts of the $3d^64s^2 a ^5D_4 - 3d^64s4p z ^5F_5^o$ Fe I resonance line at 372 nm between all four stable isotopes $^{54}$Fe, $^{56}$Fe, $^{57}$Fe, and $^{58}$Fe, as well as the complete hyperfine structure of that line for $^{57}$Fe, the only stable isotope having a non-zero nuclear spin. The field and specific mass shift coefficients of the transition have been derived from the data, as well as the experimental value for the hyperfine structure magnetic dipole coupling constant $A$ of the excited state of the transition in $^{57}$Fe: $A(3d^64s4p z ^5F_5^o) = 81.69(86)$ MHz. The measurements were done by means of Doppler-free laser saturated-absorption spectroscopy in a Fe-Ar hollow cathode using both natural and enriched iron samples. The measured isotope shifts and hyperfine constants are reported with uncertainties at the percent level.