| Abstract: | We present a joint theoretical and experimental investigation for electric-field effects on ground-state photoionization of Ca. For an electric field with its direction along the z axis, the dominant field-free, doubly excited, odd-parity (i. e., 3dnp and/or 3dnf) resonances of the (1,3)L(J=1)(o) (i.e., (1,3)P(J=1)(o) and (3)D(J=1)(o)) symmetries are coupled with the even-parity (i.e., 3dns, 3dnd, and/or 3dng) resonances of the (1,3)L(J=0)(e) (i.e., (1)S(J=0)(e) and (3)P(J=0)(e)) and (1,3)L(J=2)(e) (i.e., (3)P(J=2)(e), (1,3)D(J=2)(e), and (3)F(J=2)(e)) symmetries. Using a B-spline-based complex-rotation method with spin-dependent interaction, our theoretically calculated spectrum is found to be in good agreement with the observed spectrum from a cross-beam photoionization experiment for field strengths up to 25 kV/cm. We present in detail a number of qualitative features of the field-induced level crossing and avoided crossing in energy between neighboring resonances, their corresponding changes in width, and the resulting variation in resonance structure profiles. A few " hidden" resonances due to strong overlap with more prominant resonances are also identified theoretically. |
