S-matrix analysis of non-resonant multiphoton ionisation of inner-valence electrons of the nitrogen molecule

Abstract

We have used a strong field S-matrix theory to analyse the ionisation of inner-valence electrons of the nitrogen molecule in an intense laser pulse. The results of calculations show that the laser-induced population distribution in the electronic states of the molecular ion is shifted towards lower vibrational levels as compared to a Franck-Condon distribution. This is found to be due to the strong dependence of the rates of multiphoton ionisation on the ionisation potential. Theoretical results for the intensity dependence of the strongest band head of the first negative band system of N2+ agree with experimental data.