15min:

Z. KISIEL, L. PSZCZÓ\L KOWSKI, E. BIA\L KOWSKA-JAWORSKA, O. DESYATNYK, M. J. NOWAK, Institute of Physics, Polish Academy of Sciences, Al. Lotników 32/46, 02-668 Warszawa, Poland.

The trimer (H₂O HCl) Ar was observed in this laboratory by supersonic expansion cavity-FTMW spectroscopy, during the work carried out on H₂O...HCl and (H₂O)₂HCl. 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 HCl subunit. (H₂O HCl) Ar is near-planar and since the H₂O HCl unit is oriented at ~ 27^o to the b-inertial axis both the µ_b and the µ_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 ³⁷Cl, D, and ¹⁸O substitution, have been observed. In addition to the usual spectroscopic constants it was possible to determine accurate values of the _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 r_m method to weakly bound complexes we derived such a geometry for (H₂O HCl) 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 HCl allow the effects of this first step in inert-gas matrix isolation of H₂O HCl to be identified.