VUV photoionization of acetamide studied by electron/ion coincidence spectroscopy in the 8-24 eV photon energy range

A VUV photoionization study of acetamide was carried out over the 8-24 eV photon energy range using synchrotron radiation and photoelectron/photoion coincidence (PEPICO) spectroscopy. Threshold photoelectron photoion coincidence (TPEPICO) measurements were also made. Photoion yield curves and branching ratios were measured for the parent ion and six fragment ions. The adiabatic ionization energy of acetamide was determined as I.E. (1²A′) = (9.71 ± 0.02) eV, in agreement with an earlier reported photoionization mass spectrometry (PIMS) value. The adiabatic energy of the first excited state of the ion, 1²A″, was determined to be ≈10.1 eV. Assignments of the fragment ions and the pathways of their formation by dissociative photoionization were made. The neutral species lost in the principal dissociative photoionization processes are CH₃, NH₂, NH₃, CO, HCCO and NH₂CO. Heats of formation are derived for all ions detected and are compared with literature values. Some astrophysical implications of these results are discussed.