Knowledge Bank

The trimer $(H2O\cdots HCl)\cdots Ar$ was observed in this laboratory by supersonic expansion cavity-FTMW spectroscopy, during the work carried out on $H2O\dots HCla$ and $(H2O)2HCl.b$ The title trimer appears to be useful test-bed for detailed assessment of the effect of complexing a Rare-gas atom to the more strongly bound $H2O\cdots HCl$ subunit. $(H2O\cdots HCl)\cdots Ar$ is near-planar and since the $H2O\cdots HCl$ unit is oriented at $\approx 27\circ$ to the b-inertial axis both the $\mu b$ and the $\mu a$ dipole moment components are appreciable, giving rise to a rich rotational spectrum. Presently we present a summary of the information obtained for this trimer. Five different isotopomers of the trimer, resulting from $\mathrm{<mrow\; data-mjx-texclass="ORD">37</mrow>}Cl,D$, and $\mathrm{<mrow\; data-mjx-texclass="ORD">18</mrow>}O$ substitution, have been observed. In addition to the usual spectroscopic constants it was possible to determine accurate values of the $\chi ab$ nuclear quadrupolar splitting constant for the chlorine nucleus, and thus the principal nuclear quadrupole tensor and the associated rotation angle. Electric dipole moment of the trimer was measured and supporting ab initio calculations at the MP2/aug-cc-pVTZ level were carried out. Following a recent test of the applicability of the $rm$ method to weakly bound $complexesc$ we derived such a geometry for $(H2O\cdots HCl)\cdots Ar$ and find it to be in satisfactory agreement with the ab inito calculations. Comparison of results obtained for the trimer with the accurate data available for $H2O\cdots HCl$ allow the effects of this first step in inert-gas matrix isolation of $H2O\cdots HCl$ to be identified.