Vacuum-Ultraviolet Absorption Spectra of the Cyclic Ethers: Trimethylene Oxide, Tetrahydrofuran, and Tetrahydropyran

The vacuum-ultraviolet spectra of trimethylene oxide, tetrahydrofuran and tetrahydropyran show discrete absorption at frequencies higher than 49 000 cm—1. Rydberg series are found to converge to a first ionization potential at 77 980 cm—1 (9.667 eV), 75 960 cm—1 (9.42 eV), and 74 630 cm—1 (9.25 eV), respectively for trimethylene oxide, tetrahydrofuran, and tetrahydropyran. Analysis of the vibronic structure indicates the upper vibrational frequencies are only slightly changed from those of the ground state.