Analysis of electron diffraction data for several symmetric coordinates of large-amplitude motions in the case of the 1,3,5-trinitrobenzene molecule

A brief description of a solution of the problem on electron diffraction analysis using the potential procedure for nonrigid molecules with large-amplitude motions along several symmetric internal coordinates was given. The efficiency of the approach was demonstrated for determination of the equilibrium geometry of the 1,3,5-trinitrobenzene molecule with three equivalent internal rotation coordinates of NO2 groups. The results of the electron diffraction experiment and quantum-chemical calculation at the MP2(full)/cc-pVTZ level were considered along with the vibrational spectra of 1,3,5-trinitrobenzene and a planar equilibrium D 3h symmetry conformation for the molecule was found reliably for the first time. The geometrical parameters of the molecule were determined (r e , the bond lengths are given in A, the angles in deg): CC 1.387(2), CN 1.474(4), NO 1.220(1), CH 1.072(31), ONO 125.8(2), CC(H)C 116.6(3), HCC* 121.7(1), CC(N)C* 123.4(3), NCC* 118.3(1), and CNO* 117.1(1); the asterisk marks the dependent parameters.