Rovibrational spectroscopy of the CH + -He and CH + -He 4 complexes

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 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 . The spectrum of CH -He exhibits perpendicular transitions of a near prolate top with a band origin at 2745.9 cm , and thus confirms it to have a T-shaped structure. For CH -He , the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.