The photoionisation of the⁴S⁰ground state of atomic nitrogen

Photoionisation of the nitrogen ground state N(2s 2 2p 3 4 S 0 ) has been extensively studied starting from an accurate physical model. The initial bound state N( 4 S 0 ) and the final continuum state N + +e - ( 4 P e ) are described consistently by collisional R-matrix-type expansions over the five parent ionic states N + (2s 2 2p 2 3 P e ; 2s2p 3 5 S 0 , 3 D 0 , 3 P 0 , 3 S 0 ), represented in turn by accurate configuration interaction wavefunctions. An exact account of the couplings between the photoejection of the 2p and 2s valence electrons is essential in the low-energy spectrum, dominated by wide resonant structures. Close agreement with a recent high-resolution measurement of the strongest resonances contributes towards an assessment of the accuracy of the calculation. Detailed graphs and tables provide all the relevant information-total and partial cross sections, angular distribution of photoelectrons, analysis and fitting of prominent resonant structures-from the threshold at 852 AA ( approximately=1 Ryd) to 300 AA ( approximately=3 Ryd).