Spectroscopy of the low-frequency vibrational modes of CH3+ isotopologues

The low-frequency stretching and bending vibrations of the isotopologues CH2D+,CD2H+ and CH3+ have been recorded at low temperature and low resolution. For this, a cryogenic 22-pole trapping machine coupled to an IR beamline of the FELIX free electron laser facility has been used. To record the overview spectra, the laser induced reactions CDmHn+ + H-2 -> (hv) CDm-1Hn+1+ + HD have been applied for these species. As this scheme is not applicable to CH3+, the latter has been tagged with He and subsequently dissociated by the IR beam. For the resulting CH3+-He spectrum, broad features are observed below 1000 cm(-1) possibly related to vibrational motions involving the He atom. The extracted vibrational band positions for all species are compared to results from high-level quantum-chemical calculations. (C) 2018 Elsevier Inc. All rights reserved.