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

Abstract

This paper investigates in detail the vacuum UV photoabsorption spectrum of trans-1,2-C 2 H 2 Cl 2 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= 0.844) and nd/4f-( δ= 0.03/0.011) Rydberg states, converging to the 2a u −1 ionization continuum, to two series of np-( δ= 0.66 and 0.40) states converging to the 5a g −1 continuum, to ns-( δ= 0.983) and nd-( δ= -0.06) states converging to the 4b u −1 continuum and to two np-type ( δ= 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-C 2 H 2 Cl 2 . Assignments of the vibrational structure of some of these transitions are also proposed.

THE PHOTOELECTRON SPECTROSCOPY OF THE DICHLOROETHYLENES: THE VICINAL ISOMER trans-1,2-HClC=CHCl. QUANTUM CHEMICAL CALCULATIONS AND EXPERIMENT

“…The Δ-plot of the TPES of the X2 A u state and of the PAS of trans-1,2-C 2 H 2 Cl 2 [21] in the same energy range is reproduced in Fig. 6b.…”

“…The result is illustrated in Fig. 5a together with the Δ-plot of the photoabsorption spectrum measured in the 12-17 eV energy range [21]. The chosen ionization energies correspond to the IE ad (9.630 eV and 11.840 eV) of the first two electronic states and the TPES band maximum of the X2 A u state at 10.330 eV.…”

“…5b represents vibrationally resolved CIS spectra for the indicated internal energy of the molecular ion in its ground electronic state. The Δ-plot of the PAS between 9.5 eV and 12.2 eV has been included [21].…”

“…Recently, the analysis of Rydberg transitions observed in the vacuum UV-PAS of trans-1,2-C 2 H 2 Cl 2 [21] concluded on the basis of selection rules considerations that the probable MO sequence at increasing energy would be 4a g -1a u and 3a g -3b u . This order will be adopted in the following sections.…”

“…8b showing the abundant structure generated by threshold photoelectrons. In the same figure, the Δ-plot of the PAS of trans-1,2-C 2 H 2 Cl 2 [21] in the same photon energy range has been inserted. The close correlation is obvious.…”