Detailed studies of the first rotational spectra of mixed noble gas trimers and tetramers containing Ne and Ar atoms are described. Transitions of various isotopomers of Ne2Ar, NeAr2, Ne3Ar, Ne2Ar2, and NeAr3 were measured, Accurate values for rotational constants and centrifugal distortion constants were obtained from the spectral analyses. The spectroscopic parameters are consistent with isosceles triangular geometries of the trimer systems, and with distorted tetrahedral arrangements for the tetramers, Further evidence for the geometries was found in the effects of spin statistics in the spectra of isotopomers with C-2 upsilon symmetry and of those with C-3 upsilon symmetry, The simplicity of these fundamental systems makes them well suited for the determination and characterization of many-body nonadditive interactions. The signal strengths observed in these first high resolution spectroscopic studies of noble gas tetramers indicate the possibility of detecting the spectra of larger noble gas clusters. (C) 1997 American Institute of Physics.