Rotational spectrum and structure of the Ar3–HCl symmetric top

Abstract

The Ar₃–HCl tetramer has been identified via the observation of its microwave rotational spectrum using the pulsed nozzle Fourier transform technique. The rotational spectroscopic constants of the ground vibrational state have been obtained for the ³⁵Cl/³⁷Cl isotopes from measurements of the J=1→2 to J=4→5 transitions and their hyperfine structure. For Ar₃–H³⁵Cl, the values found for B₀, D_J, D_JK, and χ_aa are 843.8974(1) MHz, 2.333(2) and 1.818(6) kHz, and 31.006(5) MHz, respectively, and for Ar₃–H³⁷Cl, 825.9811(2) MHz, 2.211(5) and 1.940(12) kHz, and 24.481(8) MHz. The cluster is a symmetric top with the HCl along the C₃ axis, its H end directed towards the Ar₃ trimer. In its torsional oscillations, the HCl makes an average angle of 36.91° with the symmetry axis. The chlorine isotopic substitution leads to values of 3.8510 and 4.0024 Å for the Ar–Ar and Ar–Cl distances. The results of the present study are compared with those reported earlier for the Ar_m–HF (m=1,2,3) and Ar_m–HCl (m=1,2) clusters.