High-Resolution N2 Absorption Study from 730 to 980 Å

Abstract

The absorption spectrum of N2 obtained photoelectrically at a bandwidth of 0.04 Å from 730 to 980 Å is presented and compared to earlier, broader band measurements. At wavelengths longer than the ionization edge at 796 Å the peak absorption cross sections (and consequently band oscillator strengths) show a highly variable dependence on the number density of absorbing molecules in the light path, which is caused by saturation and bandwidth effects. The results of an attempt to obtain band oscillator strengths in the limit at low column numbers (1014 molecules/cm2) are given. At wavelengths shorter than the ionization edge, the data are only dependent on column number for values greater than ≈ 1016 molecules/cm2. Absolute values for a set of lower limits on the cross sections are given, the structure is identified, and results are compared to those of Cook and Metzger, Huffman et al., and Cook and Ogawa. Optical oscillator strengths are compared to those of Lawrence et al. for the four bands in the interval from 958 to 972 Å. These are the only bands for which optical oscillator strengths had been previously obtained. The results agree within experimental error with the earlier work except that the oscillator strength of the band at 972 Å is shown here to vary with absorbing column number. Oscillator strengths for a total of 102 intervals are given. They are grouped into the b 1Πu, b′ 1Σu+, c′ 1Σu+, o 1Πu, and c 1IIu vibrational band systems and are compared to normalized electron energy-loss band-head data of Geiger and Schröder. Marked perturbations in the vibration series are evident.