We report on nonresonant strong field ionization of the multielectron transition metal atoms V, Nb, Ta, Ni, and Pd. Operating in the adiabatic regime ($\lambda =1.5\mu \mathrm{m}$), we quantitatively determined both (i) the first charge state saturation intensities and (ii) the absolute ionization rates for intensities ranging from threshold up to $3\times {10}^{14}\mathrm{W}/{\mathrm{c}\mathrm{m}}^2$. We observed a dramatic suppression of ionization relative to single active electron approximation expectations. We suggest that this derives from dynamic polarization or screening effects within the multielectron atom, stressing a need for many-body theories of strong field ionization.

• Received 31 May 2004

DOI:https://doi.org/10.1103/PhysRevLett.93.213003