$K$-shell photoabsorption coefficients of ${\mathrm{O}}_2$, C${\mathrm{O}}_2$, CO, and ${\mathrm{N}}_2$O

The total photoabsorption coefficient has been measured from 500 to 600 eV around the $K$ edge of oxygen in gases ${\mathrm{O}}_2$, C${\mathrm{O}}_2$, CO, and ${\mathrm{N}}_2$O by means of a gold continuum source and crystal spectrometer with better than 1-eV resolution. The cross sections are dominated by discrete molecular-orbital transitions below the $K$-edge energy. A few Rydberg transitions were barely detectable. Broad shape resonances appear at or above the $K$ edge. Additional broad, weak features above the $K$ edge possibly arise from shake up. The authors give quantitative results that have about 10% accuracy ($3\sigma$), except on the very strong peaks. All the measured features are discussed in relation to other related measurements and theory.