Infrared Spectroscopy of CH 5 + Cations in Helium Nanodroplets

The methanium CH is a prototypical fluxional ion whose infrared spectra remain unassigned. Here we report on the infrared spectra of CH cations and its deuterated isotopomer, CH D , in helium droplets at a low temperature of 0.38 K. The ions were produced upon protonation of CH molecules, a technique that was developed in this work. The spectra of CH around 3000 cm show two strong and broad infrared bands and a weak shoulder, reflecting its highly fluxional nature. The spectrum of CH D shows a much sharper infrared band, indicating a partial quenching of the exchange of H/D atoms. This work also reports on the infrared spectrum of the methane dimer radical cations (CH ) .