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REMPI and MATI spectroscopic investigations were applied to van-der-Waals complexes of the three dichlorobenzene isomers with argon. From the REMPI spectra it is concluded that the argon atom is shifted towards the chlorine atoms during excitation for the ortho and the meta isomer while it stays in the middle of the ring for the para isomer. From the MATI spectra it was possible to determine the binding energies in the ion ground state as 617 +/- 15 cm(-1), 529 +/- 125 cm(-1) and 581 +/- 76 cm(-1) for the para, the meta and the ortho isomer, respectively. Together with theoretical calculations binding energies in the neutral ground state were determined to be 426 +/- 16 cm(-1) for all the three isomers.

For the first time, two color resonant mass analyzed threshold ionization (MATI) spectroscopy has been applied in order to investigate the ionic properties of 1,3-dichloro-2-fluoro-benzene (1,3,2-DCFB) and 1,3-difluoro-2-chloro-benzene (1,3,2-DFCB) radical cations in their electronic ground state. The ionic ground state of the different samples has been investigated via different S 1 intermediate states and compared to 1,2,3-trichlorobenzene measured in previous work. Additionally quantum chemical calculations at DFT (density functional theory) and TDDFT (time-dependent density functional theory) level of theory have been performed to support experimental findings. From the MATI spectra the adiabatic ionization energies of 1,3-dichloro-2-fluorobenzene and 1,3-fluoro-2-chlorobenzene could be determined to be 75.242 AE 6 cm À1 and 75.627 AE 6 cm À1 , respectively. Several vibrational modes of both compounds have been assigned by comparison of the experimental and theoretical results.

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