Near-infrared diode laser spectroscopy of the nitrogen molecule in Rydberg states

Abstract

Two electronic bands of the nitrogen molecule were observed by near-infrared diode laser absorption spectroscopy around the 1.3 μm region. One band was assigned to the transition from the E 3Σ+g(v″=0) to D 3Σ+u(v′=0) state. Both states were previously assigned as Rydberg states with an s- or p-electron, and an N+2 X 2Σ+g core. Fine structure constants of these states were determined for the first time. The second band looked as if it belonged to a doublet system of the molecular ion, but it turned out to be that of the neutral when the doublet structure was resolved into triplet components by means of sub-Doppler saturation spectroscopy. This band was also assigned as a 3Σ+−3Σ+ transition and was tentatively assigned to a vibrational hot band of the D–E transition based on the rotational constants, lifetime, transition dipole moment, and systematic line broadening due to predissociation.