Electronic state resolved PEPICO spectroscopy of pyrimidine

Abstract

Photoionization techniques, such as photoelectron spectroscopy (PES) and photoionization mass spectrometry (PIMS), are well-established and powerful methods for studying the spectroscopy of isolated bio-organic molecules and their fate under vacuum ultraviolet (VUV) irradiation. Measuring the energy selected electron leaving a molecular ion in coincidence with other particles, such as ions, can provide even deeper insights into the mechanisms of the interaction of molecules with ionizing radiation. We have thus implemented the electronic state resolved photoelectron photoIon coincidence (ER-PEPICO) technique in our laboratory. Here, we report our newly constructed apparatus, and its application for characterizing fragmentation processes occurring in pyrimidine. Ionization of the two highest molecular orbitals (MOs) of the valence band does not lead to fragmentation of the resulting ion. The third band observed in photoemission is due to the ionization of two MOs, and leads mainly to the formation of the parent ion. The next three electronic states are not resolved experimentally and appear as a single band; their ionization leads to fragments of mass to charge ratio m/e = 53 (C 3 H 3 N + ), while ionization of deeper lying MOs leads mostly to m/e = 26 (C 2 H + 2 ). We compare our data with previous non-coincidence photoionization results and describe the problems encountered and their solutions.

On the production of N+2ions at the N 1s edge of the nitrogen molecule

“…The limit is determined by the detector size of the ion TOF spectrometer, the length of the instrument (the drift tube is 320 mm long) and the applied electric fields in the interaction region, and corresponded to the kinetic energy of about 4 eV for N + ions under the used experimental conditions. The ion TOF spectrometer offers the time-resolving power T/ T of about 175 [21]. The sample gas was introduced into the interaction region through a hypodermic needle.…”

Ionization and photofragmentation of Ru3(CO)12 and Os3(CO)12

“…Photoelectron spectra were recorded with a commercial hemispherical electron energy analyzer (VG 220i) which was placed at the magic angle with respect to the polarization of the incoming synchrotron beam. 11,12 The analyzer was used with pass energies of 5 eV and 10 eV which provided a resolution of 100 meV for the spectra measured at low photon energies (25-60 eV) and a resolution of 200 meV for the spectra at 120 eV photon energy. For a pass energy of 5 eV, the transmission function was measured using the Auger spectrum of xenon 13,14 and was flat within ± 10% for electrons with kinetic energies between 13 and 35 eV and decreased for lower kinetic energies to 91% of the maximum transmission at 10 eV and 70% of the maximum transmission at 8 eV.…”

“…17 Mass spectra were recorded with a home-made time-offlight spectrometer and the instrument is described in detail in Ref. 11. The photon energies used were 27 eV, because it allowed using a Mg-filter with an absorption edge of 49.5 eV in order to block higher order radiation, 50 eV as intermediate photon energy still below the giant np → nd resonance in Ru 3 (CO) 12 (see below) and 120 eV which is well above all outer valence resonances.…”

“…This is not the case for 27 eV photons because of the reduced double ionization cross section close to the threshold. 42 (iii) The intensity of the low fragmentation peaks (n = [10][11][12] and especially the parent peak is too high when compared to the photoelectron spectrum (see Figure 9). In principle, this could be caused by a dissociation barrier.…”

Communication: “Position” does matter: The photofragmentation of the nitroimidazole isomers

“…The results suggest that particular products of their decomposition may influence the effectiveness of the radiosensitising action of their derivatives. The experiments are based on the photofragmentation of isolated 4(5)-and 2-nitroimidazole molecules by the tunable synchrotron radiation of the GasPhase photoemission beamline [14][15][16] at Elettra (Trieste, Italy) and the vacuum ultraviolet (VUV) radiation of a rare gas discharge lamp. 17 The setups have been described elsewhere 14,17 and more details are reported in the supplementary material.…”