Mulliken inner complexes [(CH3)3 NCl]+…F− in pre-reactive mixtures of trimethylamine and chlorine monofluoride: identification and characterisation by rotational spectroscopy

Ground-state rotational spectra of four symmetric-top isotopomers of a pre-reactive complex formed by trimethylamine and chlorine monofluoride were observed by using a fast-mixing nozzle in a Balle-Flygare microwave spectrometer. The spectroscopic constants B0, DJ, DJK, Ξaa(CL), Maa(Cl) and TrM(Cl) were determined. The observed complex has a structure of C3 or C3v symmetry, with the ionic form [(CH3)3NCl]+…F− as the main contributor to its valence-bond description, i.e. the ion Cl+ is largely transferred from ClF to N to trimethylamine on complex formation. Thus, the observed complex is of the Mulliken inner type.