The oscillator strength of the πg shape resonance in the absorption K-spectrum of a nitrogen molecule

Magnitudes of the absorption cross sections of a nitrogen molecule are measured by the transmission method near the ionization K-threshold. Based on these data, the partial absorption NK cross sections are obtained and the oscillator strength of the π_g shape resonance is determined. It is found that the oscillator strength of the π_g-resonance increases as the optical density of nitrogen decreases. This phenomenon is interpreted as a result of the instrumental distortion effect (the thickness effect). By extrapolating to zero pressure, the oscillator strength of the π_g shape resonance is determined to be 0.29.