Entrance channel X-HF (X = Cl, Br and I) complexes studied by high-resolution infrared laser spectroscopy in helium nanodroplets.

Rotationally resolved infrared spectra are reported for halogen atom-HF free radical complexes formed in helium nanodroplets. An effusive pyrolysis source is used to dope helium droplets with Cl, Br and I atoms, formed by thermal dissociation of Cl2, Br2 and I2. A single hydrogen fluoride molecule is then added to the droplets, resulting in the formation of the X-HF complexes of interest. Analysis of the resulting spectra confirms that the observed species have 2Pi3/2 ground electronic states, consistent with the linear hydrogen bound structures predicted from theory. Stark spectra are also reported for these species, from which the permanent electric dipole moments are determined.