The vibrationally resolved electronic spectrum of the s y m-trichlorobenzene radical cation in gas and condensed phases

Laser induced fluorescence excitation spectra of 1,3,5-C6H3Cl3+ have been observed in Ar and Ne matrices and in the gas phase. Resolved emission spectra while laser pumping a single vibronic level have also been observed in the matrices. Combination of the spectra in the three media show that the excitation is little perturbed by the matrix environment. Most of the upper state a′1 and e′ vibrational modes are assigned and determined with a smaller number of ground state frequencies being similarly obtained. The strong appearance of the e′ modes in the spectrum shows that the symmetry of one of the states is lowered from D3h. This is most likely caused by a Jahn–Teller distortion of the ?2E′′ state. An estimate for the barrier between the Jahn–Teller minima for mode 13 is obtained. Comparison of the upper ?2A2′′ state vibrational frequencies with those of the ground state parent molecule supports the proposal that the ? state is formed by removal of an electron from an orbital centered predominately on the Cl atoms.