Rydberg states in cyclic alkanes

Abstract

Vacuum-ultraviolet spectra in the range 50-78 kK are presented for cyclohexane, cyclohexane-d12, adamantane, and bicyclo[2.2.2]octane (1 kK = 1000 cm-1). A sharp Rydberg series leading to an ionization potential of 9.31 eV is found in adamantane. This I.P., which differs significantly from a recent low resolution photoelectron spectroscopic (PES) value, was confirmed by high-resolution PES. The Rydberg nature of the observed transitions was confirmed by pressure effect studies. Sharp Rydberg series were also found in the cyclohexanes and I.P.'s of 9.88 eV for C6H 12 and 9.91 eV for C6D12 were measured. A Rydberg series leading to an I.P. of 9.43 eV was found in bicyclo[2.2.2]octane. The I.P. was checked using high-resolution PES. A sharp transition not fitting into this series was found to be definitely a Rydberg using pressure effect and was assigned to a separate series. A weak sharply structured transition in cyclobutane is presented and assigned as a symmetry forbidden Rydberg. The orbital natures of the Rydberg excited states are discussed.