Photoionization of 1,3-Butadiene, 1,2-Butadiene, Allene, and Propyne

Abstract

Using a photoionization mass spectrometer, the ionization potentials of the parent molecules and the appearance potentials of the fragment ions, observed below 13 eV, have been determined for 1,3-butadiene, 1,2-butadine, allene, and propyne. The ionization potentials of 1,3-butadiene are 9.07 ± 0.02 eV, 9.80 ± 0.04 eV, and 11.7 ± 0.04 eV. The adiabatic ionization potential of 1,2-butadiene is 9.23 ± 0.02 eV. The adiabatic ionization potential of allene is 9.62 ± 0.04 eV. The ionization potentials of propyne are 10.38 ± 0.02 eV and 11.30 ± 0.02 eV. The heat of formation of C3H3+ and C4H5+ is calculated to be 11.18 ± 0.04 eV and 10.45 ± 0.04 eV, respectively. Derived bond energies for the ionic states are given. The data are shown to be consistent with rearrangement of 1,3-butadiene via hydrogen migration in the excited molecular ion. At threshold for fragmentation, the C4H5+ and C3H3+ ions from 1,3-butadiene and 1,2-butadiene are identical.