The experimental electric dipole moments of the ArnHX van der Waals clusters

The electric dipole moments of the clusters Ar2HF, Ar3HF, Ar2HCl, Ar3HCl, and Ar2HBr have been determined from Stark effect measurements with a cavity Fourier Transform Microwave spectrometer. Intercomparison of the dipole moments in a given series, e.g., 1.1085(5), 0.811714(16), 0.9304(14), 0.9827(23) D for ArnHCl, n=0,1,2,3, respectively, reveals recovery of the dipole moment with cluster size increasing above n=1. Preliminary interpretation shows that this effect is almost entirely due to the decrease in vibrational averaging due to stronger binding of the HCl subunit in the larger clusters. The effective induced dipole moment in the vibrational ground state of these clusters is rather small and shows minimal changes with cluster size.