Toluene Valence and Rydberg Excitations as Studied by <i>ab initio</i> Calculations and Vacuum Ultraviolet (VUV) Synchrotron Radiation

The electronic spectroscopy of isolated toluene in the gas phase has been investigated using high-resolution photoabsorption spectroscopy in the 4.0–10.8 eV energy range, with absolute cross-section measurements derived. We present the first set of ab initio calculations (vertical energies and oscillator strengths), which we use in the assignment of valence and Rydberg transitions of the toluene molecule. The spectrum reveals several new features not previously reported in the literature, with particular relevance to 7.989 and 8.958 eV, which are here tentatively assigned to the π*­(17a′) ← σ­(15a′) and 1π*­(10a″) ← 1π­(14a′) transitions, respectively. The measured absolute photoabsorption cross sections have been used to calculate the photolysis lifetime of toluene in the upper stratosphere (20–50 km)