Helium Nanodroplet Infrared Spectroscopic Studies of CH 4 + and 13 CH 3

In this work, CH cations were formed in helium droplets and investigated with infrared laser spectroscopy. The observed infrared bands are assigned to the C isomer of the CH cation. The rotational structure of the bands remains unresolved, indicating a factor of 3 or larger decrease in the rotational constants in helium nanodroplets. We also report on the observation of the spectrum of isotopically substituted CH cations in He droplets, which shows a well-resolved rotational structure. The rotational constant A for rotation about the C axis of CH in helium was found to be a factor of 1.17 smaller than in the gas phase.