Gas-phase conformational analysis of 1,4,7-trithiacyclononane

Conformational analysis of 1,4,7-trithiacyclononane, [9]aneS₃, in the gas phase was done using three techniques: ab initio molecular orbital calculations at the UF and MP2 levels as well as microwave and photoelectron spectroscopies. The photoelectron spectroscopic data show evidence for at least two conformations with different ionization energies. Using the calculated photoelectron spectra, the observed sulfur 3p ionization peaks can be assigned to C₁ and C₂ conformations. Forty of the observed microwave transitions can be assigned to a C₁ symmetry, asymmetric top, rigid rotor spectrum with rotational constants A = 1155.651(3) MHz, B = 998.442(3) MHz, and C = 629.426(2) MHz. Additional microwave lines are believed to be due to a nonrigid C₂ symmetry conformation. No significant populations of conformers of higher symmetry are found.