Ar XIII is found to be unique with new features in electron-ion recombination not seen in any other ion .
The ion has been studied with the unified method which provides a theoretically self-consistent set of atomic parameters for the inverse processes of photoionization and total electron-ion recombination .
Unified method subsumes both the radiative recombination ( RR ) and dielectronic recombination ( DR ) within the framework of close-coupling formulations using the R-matrix method .
A set of four DR ” bumps ” , two in the low and two in the high temperature regions , is found to exist in the recombination rates of Ar XIV + e \rightarrow Ar XIII .
This is in contrast to two typical DR ” bumps ” , one at high temperature common for most ions and one at low temperature depending on the presence of near threshold autoionizing resonances in the bound-free process .
Large scale ab initio calculations have been carried out for photoionization and electron-ion recombination cross sections of Ar XIII .
The ion is represented by a large close coupling eigenfunction expansion of 37 core Ar XIV states from n = 2 and 3 complexes .
This enables core excitations of type \Delta n = 0 and 1 .
The \Delta n = 1 transitions have much higher radiative decay rates than those of \Delta n = 0 , and cause the fourth DR bump around 2 \times 10 ^ { 6 } K. For a large number of bound states , Ar XIII exhibits more extensive resonant structures and wider PEC ( photoexitation-of-core ) resonances for n = 3 core states than those of n = 2 states .
Hence the high energy region of photoionization and recombination are dominated by these structures .
A total of 684 bound states with valence electron n \leq 10 and l~ { } \leq 9 are found for Ar XIII .
Total and partial photoionization cross sections of all bound states , state-specific recombinaion rates of 561 bound states and total recombination rate coefficients at a large temperature range are presented for Ar XIII .