A study of the valence shell spectroscopic and thermodynamic properties of thiophene by photoabsorption and photoion spectroscopy

The valence shell spectroscopic and thermodynamic properties of thiophene have been investigated through photoabsorption and ion fragmentation studies. The absolute photoabsorption cross-section has been measured between the ionisation threshold and 35 eV using a double ion chamber and synchrotron radiation. New Rydberg series converging onto either the B∼2A1 or the G∼2A1 limits have been observed. The photoabsorption spectrum is dominated by broad features due to intravalence transitions, and tentative assignments have been proposed based upon a term value analysis. Time-of-flight mass spectra have been recorded in the photon energy range 12-28 eV and these have allowed the appearance energies for 18 fragment ions and the doubly charged parent ion to be determined. Molecular orbital calculations have been performed to compute the energies of several neutral or ionic species relevant to the lowest energy fragmentation channel. These energies, when compared with the experimental data, help to define the ion formation mechanisms