Detection of small concentrations of N2+ in the atmosphere by a laser scattering technique

The resonance absorption and emission at atmospheric pressure from the first negative band in N2+ has been investigated by a laser technique. By stimulation with a narrow-bandpass dye laser the cross section for resonance absorption at 3914 Å and subsequent emission at 4278 Å, (0-1) transition, was measured. This cross section was determined to be 3×10−20 cm2/ion. A theoretical estimate for this process places the cross section at 1.8×10−21 cm2/ion. An analysis of both the experiment and the calculation indicates that these numbers represent the upper and lower limits for the actual value of the cross section.