Comparison of intense-field ionization of diatomic molecules and rare-gas atoms

Strong, short laser pulses have been used to ionize diatomic molecules and rare-gas atoms. Using mixed species targets, intensity-dependent ionization yield ratios have been measured directly for pairs of molecules and atoms with similar ionization potentials. Specifically, ionization rate ratios for homonuclear $({\mathrm{N}}_{2}:\mathrm{Ar},{\mathrm{F}}_{2}:\mathrm{Ar},{\mathrm{D}}_{2}:\mathrm{Ar},{\mathrm{O}}_{2}:\mathrm{Xe},{\mathrm{S}}_{2}:\mathrm{Xe})$ and heteronuclear (CO:Kr, NO:Xe, SO:Xe) molecules have been obtained. Our experimental results are compared to the predictions of several approximate theoretical models. In general, these models fail to accurately describe the detailed differences in the intense laser ionization rates of atomic and diatomic targets.