The photoionisation of the 4S0 ground state of atomic nitrogen

Photoionisation of the nitrogen ground state N(2s22p3 4S0) has been extensively studied starting from an accurate physical model. The initial bound state N(4S0) and the final continuum state N++e-(4Pe) are described consistently by collisional R-matrix-type expansions over the five parent ionic states N+(2s22p2 3Pe; 2s2p3 5S0, 3D0, 3P0, 3S0), 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).

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