The radiation damage of biomolecules, in particular with aliphatic compound, has been extensively studied. Morpholine is a typical six-membered aliphatic heterocyclic compound. In the present work, photoionization and dissociation of the morpholine monomer and subsequent fragmentations have been investigated by synchrotron vacuum ultraviolet photoionization mass spectrometry and theoretical calculations. The vertical ionization energy of morpholine monomer is 8.37±0.05 eV, which agrees reasonably well with a theo-retical value 8.41 eV of morpholine. Experimentally observed fragmentation of morpholine ( m/z =87 amu) gives rise to m/z =86 amu, m/z =57 amu, and m/z =29 amu. Based on experimental and theoretical results, it is found that the m/z =86 amu is produced by losing H atom, the m/z =57 amu is formed by the elimination of CH 2 O with a ring-opening process, the m/z =29 amu is generated by further dissociation of the fragment m/z =57 amu (C 3 H 7 N) + by the elimination of C 2 H 4 . This finding would provide valuable insight into the photo-damage of aliphatic compounds, which may be related to living cells and other biological system.
Photoionization and dissociation of the 1-propanol dimer and subsequent fragmentations have been investigated by synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry and theoretical calculations. Besides the protonated monomer cation (C3H7OH)·H+ (m/z = 61) and Cα–Cβ bond cleavage fragment CH2O·(C3H7OH)H+ (m/z = 91), the measured mass spectrum at an incident photon energy of 13 eV suggests a new dissociation channel resulting in the formation of the (C3H7OH)·H+·(C2H5OH) (m/z = 107) fragment. The appearance energies of the fragments (C3H7OH)·H+, CH2O·(C3H7OH)H+ and (C3H7OH)·H+·(C2H5OH) are measured at 10.05 ± 0.05 eV, 9.48 ± 0.05 eV, and 12.8 ± 0.1 eV, respectively, by scanning photoionization efficiency (PIE) spectra. The 1-propanol ion fragments as a function of VUV photon energy were interpreted with the aid of theoretical calculations. In addition to O–H and Cα–Cβ bond cleavage, a new dissociation channel related to Cβ–Cγ bond cleavage opens. In this channel, molecular rearrangement (proton transfer and hydrogen transfer after surmounting an energy barrier) gives rise to the generated complex, which then dissociates to produce the mixed propanol/ethanol proton bound cation (C3H7OH)·H+·(C2H5OH). This new dissociation channel has not been reported in previous studies of ethanol and acetic acid dimers. The photoionization and dissociation processes of the 1-propanol dimer are described in the photon energy range of 9–15 eV.
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