Rotational spectra of Ar2–DCl and Ar3–DCl, and a pseudotriatomic force field for Ar2–H/DX

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Abstract
Microwave rotational transitions have been observed for Ar2–D35Cl and Ar3–D35Cl/37Cl. The Cl and D hyperfine interactions have been analyzed and rotational constants determined. The structures of the clusters are similar to those reported earlier for Ar2–HF/Cl and Ar3–HF/Cl. Ar2–D35Cl is a T‐shaped asymmetric top with the DCl along the C2v axis. The A, B, and C rotational constants are 1735.0958(5), 1651.6749(8), and 840.5459(1) MHz, respectively. The four independent centrifugal distortion constants, τaaaa, τbbbb, τaabb, and τabab, are −0.1171(3), −0.0763(2), 0.037 64, and −0.060 88 MHz. The 35Cl quadrupole interaction is anisotropic and slightly Jdependent, with a χaa of −38.184 0(7) and (1/(6)1/2)(χbb−χcc) of −1.3380 MHz for the 101→202 transition. χaa(D) was found to be 111.4 kHz. Ar3–DCl is a symmetric top with the DCl along the C3v axis. B0, DJ, DJK, χaa(35Cl), and χaa (D) for Ar3–D35Cl are 840.2264 MHz, 2.268 and 1.921 kHz, and −39.717(3) and 0.128(4) MHz, respectively. Analysis of the change in B0 with 35Cl/37Cl substitution shows conclusively that the DCl is oriented with the D end closest to the argons. A pseudotriatomic, bent XY2 model is used with the centrifugal distortion constants of Ar2–H/DF and –H/DCl to predict force constants, vibrational frequencies, and inertial defects of the four clusters. The predicted Ar–Ar stretching frequency of 21.8 to 23.0 cm−1 in the clusters compares favorably with the 25.7 cm−1 experimental value reported for free Ar2.