| Protonated methane, CH+5 , has a highly unusual structure. Ab initio calculations suggest there are three non-equivalent, lowest energy equilibrium structures that have nearly identical energies, and that the 5 protons scramble freely around the central carbon atom. While the reactivity of CH+5 has been studied experimentally and is relatively well understood, the structure of this molecule has proven to be extremely elusive to experimentalists. Many theoretical papers have been published on the quantum mechanics of the system, but a better understanding requires spectral data.;A complex, high-resolution infrared spectrum of CH+5 corresponding the C-H stretching band in the 3.4 micrometer region is reported. This is the first reported spectroscopic observation of CH+5 at any wavelength. Although detailed assignment of the individual lines has not been made, comparison with other carbocation spectra strongly suggests that the transitions are due to CH+5 . The high resolution infrared spectrum may eventually lead to an improved understanding of the dynamics of this system. Furthermore, the spectrum of protonated methane may serve as a prototype spectroscopic model for understanding the 5 equivalent proton system, just as water, ammonia, and methane have served as models for understanding 2, 3, and 4 equivalent proton systems in the past. |
