Does Tetrahydrofuran Ring Open upon Ionization and Dissociation? A TPES and TPEPICO Investigation

The threshold photoelectron spectrum (TPES) of tetrahydrofuran (THF) is compared to that of the unsaturated furan molecule. In general, there is a similarity in the orbital ionization profile for the two species, though unlike furan, THF exhibits (modest) vibrational detail only in the (9b)−1 X 2B band. An adiabatic ionization energy of 9.445 ± 0.010 eV has been derived from the onset of the TPES spectrum. Threshold photoelectron photoion coincidence spectroscopy was used to explore the loss of a hydrogen atom from ionized THF over the photon energy range of 9.9−10.4 eV. RRKM fitting of the resulting breakdown curves yields an E0 of 0.85 ± 0.03 eV (82 ± 3 kJ mol−1) (AE = 10.30 ± 0.04 eV). If the G3 IE of 9.48 eV is used to convert the experimental data from photon energy to THF ion internal energy, E0 = 0.81 ± 0.01 eV (78 ± 1 kJ mol−1). The latter value is closer to the G3 E0 of 72 kJ mol−1 for the formation of the cyclic ion 1. A variety of ring-opening reactions were also probed at the B3-LYP/6-31+G(d)...