The electronic states of ethylene oxide studied by photoabsorption andab initiomultireference configuration interaction calculations

Abstract

The absolute photoabsorption spectrum of ethylene oxide (C2H4O) has been measured between onset and 30 eV, using monochromated synchrotron radiation. Below the ionization threshold (10.56 eV) the spectrum is dominated by sharp peaks related to excitation of Rydberg series converging on the first ionization energy. Above the ionization threshold, valence-excited states, which give rise to broad bands, predominate. Underlying Rydberg states are signalled in weak vibrational structure on the valence bands. Ab initio multireference configuration interaction (MRDCI) calculations have been carried out to assist in assignment of the excited states, both valence and Rydberg. The lowest-lying valence state is electric-dipole forbidden; the first optically allowed valence state lies close to the ionization onset. The spectrum of the oxide is compared with those of cyclopropane (C3H6) and ethylene sulphide (C2H4S).

The valence shell electronic states of trimethylene oxide studied by photoabsorption andab initiomultireference configuration interaction calculations

“…These analyses show that, of the n=3 Rydberg orbitals, all except two (3da 1 and 3da 2 ) have mixed l character (where l is the orbital angular momentum) so that strong configuration interaction can be expected in the Rydberg states. A similar behaviour was observed for the related molecules ethylene oxide [9], ethylene sulphide [10] and trimethylene sulphide [11.…”

“…However, from the available data, most of the intensity may be attributed to valence transitions, including 4b 2 →10b 2 and 8a 1 →18a 1 .Above the ionization threshold, broad overlapping bands, due to intravalence transitions, dominate the photoabsorption cross section of trimethylene oxide and contributions from Rydberg excitations are weak. A similar behaviour is observed in ethylene oxide[9], ethylene sulphide[10] and trimethylene sulphide[11]. In each of these molecules an intense structureless peak, which appears to share a common origin, occurs between 12 and 13 eV,The origins of the two allowed 3b 1 →3p transitions fall at 7.111 eV and 7.654 eV.…”

“…The Rydberg behaviour observed in trimethylene oxide resembles that in the three-membered ring ether, ethylene oxide [9]. However, the valence patterns are different.…”

“…There are thus both pure and applied reasons for exploring the electronic structure of this class of compound. The present work follows from similar studies on other small-ring systems, namely cyclopropane [8], ethylene oxide [9], ethylene sulphide [10] and trimethylene sulphide [11]. Assuming C 2v symmetry, and with the molecule lying in the yz plane, the ground state electronic configuration is, from the present work:-…”

Photoionization cross sections of Ethylene oxide

“…Some other photoionization works measured relative cross sections [18], ionization efficiency [19], photodissociation with mass spectroscopy [20], photoelectronphotoion coincidence [21] and calculated vertical ionization [22]. Also, a photoabsorption study shows the relative importance of above-threshold autoionization when compared with direct ionization [23]. The electron momentum spectroscopy was used to measure the momentum distribution profile for outer valence orbitals and binding energies, which were compared with theoretical calculations in Hartree-Fock [24] and density functional theory (DFT) levels [25].…”