(N2O)(2)center dot SO2: Rotational spectrum and structure of the first vander Waals trimer containing sulfur dioxide

The trimer (N2O)(2). SO2 has been studied by Fourier transform microwave sp ectroscopy. The rotational constants for the normal species are A=1369.1014 (11) MHz, B=1115.5816(11) MHz, and C=730.5790(4) MHz. Five isotopomers of t he complex have been studied, allowing a determination of its structure. Th e configuration aligns the centers-of-mass of the three monomers in an appr oximate equilateral triangle. The monomers twist relative to this plane so that the two N2O's are intermediate between T-shaped and crossed rather tha n the usual slipped-parallel planar. The SO2 is oriented so that its oxygen s are straddling one N2O (similar to the N2O . SO2 dimer), while its sulfur is closest to the oxygen end of the other N2O. The dipole moment of ((N2O) -N-15)(2). SO2 was measured, giving mu(a)=0.606(1) D, mu(b)=1.256(2) D, mu( c)=0.058(2) D, and mu(total)=1.396(2) D. A semiempirical model has been use d to predict the trimer structure, and comparison is made with this model a s well as with the dimer N2O . SO2. (C) 2000 American Institute of Physics. [S0021-9606(00)01520-8].