Single-color optical-selectivity calculations are carried out for a number of transitions in the 570–620-nm wavelength range by a spectral-simulation method. The computed isotope ratio-enhancement factors are in good agreement with the values reported [J. Opt. Soc. Am. B 5, 2409–2416 (1988); Chem. Phys. Lett.118,134–139 (1985)]. The study results in the identification of six first-step excitation transitions for the selective ionization of the ⁹¹Zr isotope, for which the isotope ratio-enhancement factors are~10.The 4d²5s²³F₄586.8268 nm4d²5s⁵p ⁵F₅⁰ transition is found to be most efficient for selective excitation of the ⁹¹Zr isotope, whose isotope ratio-enhancement factor was nearly eight times greater than that of the previously reported transitions. The present calculations demonstrate the feasibility of selective excitation of the ⁹¹Zr isotope, despite the utilization of broadband lasers and larger Doppler widths of the atomic system.