(N2O)2⋅SO2:(N2O)2⋅SO2: Rotational spectrum and structure of the first van der Waals trimer containing sulfur dioxide

Abstract

The trimer (N2O)2⋅SO2(N2O)2⋅SO2 has been studied by Fourier transform microwave spectroscopy. The rotational constants for the normal species are A = 1369.1014(11) MHz,A=1369.1014(11)MHz, B = 1115.5816(11) MHz,B=1115.5816(11)MHz, and C = 730.5790(4) MHz.C=730.5790(4)MHz. Five isotopomers of the complex have been studied, allowing a determination of its structure. The configuration aligns the centers-of-mass of the three monomers in an approximate equilateral triangle. The monomers twist relative to this plane so that the two N2OsN2Os are intermediate between T-shaped and crossed rather than the usual slipped-parallel planar. The SO2SO2 is oriented so that its oxygens are straddling one N2ON2O (similar to the N2O⋅SO2N2O⋅SO2 dimer), while its sulfur is closest to the oxygen end of the other N2O.N2O. The dipole moment of (15N2O)2⋅SO2(15N2O)2⋅SO2 was measured, giving μa = 0.606(1) D,μa=0.606(1)D, μb = 1.256(2) D,μb=1.256(2)D, μc = 0.058(2) D,μc=0.058(2)D, and μtotal = 1.396(2) D.μtotal=1.396(2)D. A semiempirical model has been used to predict the trimer structure, and comparison is made with this model as well as with the dimer N2O⋅SO2.N2O⋅SO2. © 2000 American Institute of Physics.