Detailed analysis of the cation ground state of three dichlorobenzenes by mass analyzed threshold ionization spectroscopy

Abstract

Two color resonant mass analyzed threshold ionization (MATI) spectroscopy was applied in order to investigate the ionic properties of the structural isomers of dichlorobenzene above the ionization threshold. A detailed analysis of the vibrational properties of the two main chlorine isotopomers of each isomer was performed resulting in a precise picture of the vibrational states in the cation ground states. The general features of the two investigated isotopomers turned out to be quite similar, although some vibrational modes are slightly different up to a few wavenumbers, except for the 6b normal mode of p-dichlorobenzene. There the spectrum of the ³⁵Cl₂-isotopomer shows several additional peaks compared to the one of the ³⁵Cl³⁷Cl-isotopomer. An explanation for the extraordinary observance is discussed. In addition to the examination of the ionic ground state the measured and calculated frequencies were used to confirm the former assignment of the vibrations in the S₁ state, especially with respect to a Herzberg–Teller coupling as observed in benzene.