Role of higher multipoles in field-induced continuum lowering in plasmas

The latest development in calculations of a continuum lowering (CL) in plasmas is based on the employment of dicenter models of the plasma state. One such theory--a percolation theory--calculated the CL defined as an absolute value of energy at which an electron becomes bound to a macroscopic portion of plasma ions (a quasi-ionization). We derived analytically the value of the CL in the ionization channel, which was disregarded in the percolation theory: a quasimolecule, consisting of the two ion centers plus an electron, can become ionized in the true sense of the word before the electron would be shared by more than two ions. We derived the CL in this channel for an arbitrary ratio of charges of the two Coulomb centers, while the specific values of the CL in the percolation theory were obtained only for dicenters consisting of two identical ions. We produced our results within a purely classical approach, but proceeding from first principles. We also showed that whether the electron is bound primarily by the smaller or by the larger out of two positive charges makes a dramatic qualitative and quantitative difference for this ionization channel. This difference is revealed due to our allowance for all higher multipoles.