Knowledge Bank

Microwave spectra of complexes bearing molecular ions. $Ar-D3+/HD2+$ and $Ar-HCO4+$ were explored in a jetcooled condition. The ionic complexs were formed by a pulsed electric discharge in a supersonic expansion. Their transitions were observed in the centimeter-wave region (7-40 GHz) with a Fourier-transform microwave spectrometer, guided by the previous millimeter-wave study in a static $cella$ or the recent infrared photodissociation study in a mass-selected ion $beam.b$ For $Ar-HCO+$, rotational transitions of mono-substituted species on H. C. and O were also measured. The isotope substitution has confirmed the linear $Ar\dots H-C-O$ configuration with the Ar...H distance of 2.13 \AA. The centrifugal-distoration constant for $Ar-HCO-$ is two order of magnitude smaller than that for Ar-HCN. indicating much stronger binding in the ionic complex than the isoelectronic neutral counterpart.