The vacuum UV photoabsorption spectroscopy of the trans-dichloroethylene (1,2-ClHC=CClH) in the 5-20 eV range: Experiment and theory

This paper investigates in detail the vacuum UV photoabsorption spectrum of trans-1,2-C₂H₂Cl₂ in the 5-20 eV range using synchrotron radiation. Quantum chemical calculations are applied to the electronic transitions. Particular attention has been paid to the 2a_u(π)→2b_g(π*) transition included in the broad band observed at 6.30 eV. The Rydberg 2a_u(π)→R3s transition is presumably observed at 6.27 eV. Below 6.0 eV the structure(s) are assigned to π→σ* transition(s). The abundantly structured spectrum observed between 7.0 eV and 12.0 eV has been analyzed in terms of vibronic transitions to ns- (δ bar=0.844) and nd/4f- (δ bar=0.03/0.011) Rydberg states, converging to the 2a_u^-1 ionization continuum, to two series of np- (δ bar= 0.66 and 0.40) states converging to the 5a_g^-1 continuum, to ns- (δ bar=0.983) and nd- (δ bar= -0.06) states converging to the 4b_u^-1 continuum and to two np-type (δ bar= 0.51 and 0.26) series converging to the 1b_g^-1 continuum. These data are complemented by an analysis of the vibrational structure of the individual Rydberg states. Comparisons with previously reported values are provided. Several other spectral features Table S2 (see Supplementary Material) in the 12-20 eV range are tentatively assigned to transitions to Rydberg states converging to higher ionic excited states of trans-1,2-C₂H₂Cl₂. Assignments of the vibrational structure of some of these transitions are also proposed.