Rovibrational spectroscopy of the CH+-He and CH+-He4 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+-He4 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+-He4, the C-H stretch along the symmetry axis of this oblate top results in parallel transitions.