High-resolutionK-shell photoabsorption measurements of simple molecules

K-shell photoabsorption spectra of CO, ^13C^18O, NO, O₂, CO₂, N₂O, C₂H₂, C₂D₂, C₂H₄, C₂D₄, C₂H₆, C₂D₆ measured with unprecedented energy resolution and signal-to-noise ratio are presented. These spectra reveal many new features in core-excited valence and Rydberg states. Detailed vibrational structures are observed in these spectra, providing valuable information on the geometrical and vibrational properties of the core-excited molecules. In addition, C 1s and N 1s core-hole lifetimes are found to be 120 and 135 meV in these molecules with little dependence on their bonding environments. These results and the tentative peak assignments are discussed briefly in terms of the equivalent core model, multielectron excitations, exchange interactions, and the geometry of the excited molecules.