JAHN-TELLER EFFECTS IN SUBSTITUTED BENZENE-CATIONS .3. GAS-PHASE EMISSION-SPECTRUM OF SYM-C6CL3H3+

The gas phase emission spectrum of 1, 3, 5-C6Cl3H+3 was obtained in a discharge tube. Vibronic analysis involving correlation of ion fundamental frequencies with those of parent molecules enables a detailed comparison to be made between the vibrational structure of the spectrum of the trichloro-ion and that of 1, 3, 5-C6F3H+3. Analogous Jahn-Teller effects are shown to take place in the ground state of the two ions. The same linear coupling model is used and two possible solutions for D6 and ω6 are obtained by fitting the first two intervals in the 60,0v 1 2 progression in 1, 3, 5-C6Cl 3H+3: (i) D6 = 0.05 - 0.08, ω6 = 455 - 447 cm-1, (ii) D6 = 0.39 - 0.49, ω6 = 399 - 392 cm-1. Arguments based on previously established criteria, and applied here to the case of the 1, 3, 5-C6Cl3H+3 ion are given to select set (ii) as being far more satisfactory in interpreting the experimental data. Fitting to a larger number of bands gave D6 = 0.45, ω6 = 395 cm-1. The Jahn-Teller potential energy barrier EJT6 = 178 cm-1 is about three times greater than in the 1, 3, 5-trifluorobenzene ions, but sufficiently small for the dynamic Jahn-Teller effect to be operative in 1, 3, 5-C6Cl3H+3. Some remarks are made concerning assignments in the excitation spectrum and matrix fluorescence analyses. © 1979.