Rovibrational spectroscopy of the CH

A cryogenic 22-pole ion trap apparatus is used in combination with a table-top pulsed IR source to probe weakly bound CH(+)-He and CH(+)-He(4) complexes by predissociation spectroscopy at 4 K. The infrared photodissociation spectra of the C–H stretching vibrations are recorded in the range of 2720–2800 cm(−1). The spectrum of CH(+)-He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm(−1), and thus confirms it to have a T-shaped structure. For CH(+)-He(4), the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.