The infrared spectrum of the adamantyl cation

This Letter reports the gas phase infrared spectrum (500–1600 cm−1) of the adamantyl cation ( C 10 H 15 + ) , the dehydrogenated cation of adamantane. The experimental spectrum is in reasonable agreement with the recently reported theoretical spectrum for the 1-adamantyl isomer [G. Yan, N.R. Brinkmann, H.F. Schaefer, J. Phys. Chem. A 107 (2003) 9479]. An inclusion of vibrational anharmonicities in the linear absorption spectrum to yield a multiple-photon dissociation spectrum improves the theoretical to experimental fitting considerably. The prevalence of the 1-adamantyl isomer, as opposed to the 2-adamantyl isomer, can be rationalized by its lower calculated energy (0.49 eV).