State-selective ionization of nitrogen in the X 2Σ+g v+=0 and v+=1 states by two-color (1+ 1) photon excitation near threshold

Efficient generation of N+2X 2Σ+g(v+=0,1) is demonstrated by an extreme-ultraviolet +visible (1+1) photon excitation scheme. The c′4 1Σ+u (v′=0,1) Rydberg states are used as intermediates. The N2 molecules are ionized near the v+=0 and v+=1 ionization thresholds. The autoionizing ndδg 1Δg Rydberg series with the rotational quantum numbers N=4, 5, and 6 (in the limit of l uncoupling) are observed for the first time. Extrapolation of the N=4 series yields an ionization energy of N2 of 125 666.959(67) cm−1.