Energy- and angle-resolved non-resonant 2-photon single valence ionization of N$_2$ using 9.3 eV femtosecond pulses

We present an experimental and theoretical study on the photoionization dynamics of non-resonant 2-photon single valence ionization of molecular nitrogen. Using 30 femtosecond 9.3 eV pulses produced via 400 nm driven high harmonic generation and a 3-D momentum imaging spectrometer, we detect the photoelectrons and ions produced from 2-photon ionization in coincidence. Photoionization populates nitrogen’s X($^2\Sigma_g^+$), A($^2\Pi_u$) and B($^2\Sigma_u^+$) ionic states, where the photoelectron angular distributions of the X($^2\Sigma_g^+$) and A($^2\Pi_u$) states both vary with changes in electron kinetic energy of only a few hundred meV, which we attribute to 2-electron resonances. These results are compared against time-dependent full ab initio calculations.