Photoabsorption windows for Na andNa2+

Abstract

There exist absorption windows (i.e., Cooper-minima) in the photoabsorption cross sections of some atomic systems because of the relative phase shifts between the initial and final state wave functions due to the atomic screening potentials in contrast to the Coulomb potentials. Such window positions are sensitive to the accuracy of the initial and final state wave functions. Using our modified Breit-Pauli $R$-matrix code, the photoionization cross sections of ground Na are calculated. Our calculated cross sections and minimum position in the low photoelectron energy range $(l9\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$ are in excellent agreement with the experimental results. In the high energy range $(g9\phantom{\rule{0.3em}{0ex}}\mathrm{eV})$, there is an abnormal bump in the experimental measurements, which is a long-standing experimental puzzle. It is interesting to note that there is also an absorption window in the photoabsorption (i.e., photodissociation) cross sections of $\mathrm{Na}_{2}{}^{+}$. Such an absorption window provides an answer to the puzzle.