High resolution rotational spectroscopy of weakly bound ionic clusters:ArH3+,ArD3+

The first high-resolution study of weakly bound cluster ions is reported. The millimeter- and submillimeter-wave rotational spectra of ${\mathrm{ArH}}_3$ ${\mathrm{}}^{+}$ and ${\mathrm{ArD}}_3$ ${\mathrm{}}^{+}$ have been observed in a magnetically confined, liquid-nitrogen–cooled glow discharge and a partial molecular structure has been derived from their analysis. ${\mathrm{ArH}}_3$ ${\mathrm{}}^{+}$ appears to be planar, with the Ar atom lying on a symmetry axis of the ${\mathrm{H}}_3$ ${\mathrm{}}^{+}$ equilateral triangle, 2.38 Å from the ${\mathrm{H}}_3$ ${\mathrm{}}^{+}$ centroid. SPlitting of some of the lines is strong evidence for tunneling motion.