Marcin Dampc

The Open University (UK), Milton Keynes, England, United Kingdom

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Publications (14)22.72 Total impact

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    ABSTRACT: Multi-photon ionisation (MPI) and electron impact ionisation (EII) mass spectrometry experiments have been carried out to probe unimolecular and intermolecular reactivity in hydrated adenine clusters. The effects of clustering with water on fragment ion production from adenine have been studied for the first time. While the observation of NH4+ fragments indicated the dissociation of protonated adenine, the dominant hydration effects were enhanced C4H4N4+ production and the suppression of dissociative ionisation pathways with high activation energies. These observations can be attributed to energy removal from the excited adenine radical cation via cluster dissociation. Comparisons of MPI and EII measurements provided the first experimental evidence supporting hypoxanthine formation in adenine-water clusters via theoretically predicted barrierless deamination reactions in closed shell complexes.
    International Journal of Mass Spectrometry. 05/2014; 365-366(Special issue: Tilmann Mäerk):194-199.
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    ABSTRACT: Multi-photon ionization (MPI) of the RNA base uracil has been studied in the wavelength range 220-270 nm, coinciding with excitation to the S2(ππ∗) state. A fragment ion at m∕z = 84 was produced by 2-photon absorption at wavelengths ≤232 nm and assigned to C3H4N2O(+) following CO abstraction. This ion has not been observed in alternative dissociative ionization processes (notably electron impact) and its threshold is close to recent calculations of the minimum activation energy for a ring opening conical intersection to a σ(n-π)π∗ closed shell state. Moreover, the predicted ring opening transition leaves a CO group at one end of the isomer, apparently vulnerable to abstraction. An MPI mass spectrum of uracil-water clusters is presented for the first time and compared with an equivalent dry measurement. Hydration enhances certain fragment ion pathways (particularly C3H3NO(+)) but represses C3H4N2O(+) production. This indicates that hydrogen bonding to water stabilizes uracil with respect to neutral excited-state ring opening.
    The Journal of Chemical Physics 12/2013; 139(24):244311. · 3.12 Impact Factor
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    ABSTRACT: The electron impact mass spectroscopy and the total ion collection measurements were used to investigate the ionization and ionic fragmentation of the pyrimidine, C4H4N2, molecules in the gas phase. The cation mass spectra were measured in the 10−85 amu range and the observed mass peaks assigned to corresponding ionic fragments. The most abundant cation in the mass spectra is the parent cation, C4H4N \hbox{$_{\mathrm{2}}^{\mathrm{+}}$} + 2 , at 80 amu. The appearance energies of the ionic fragments were determined and the possible fragmentation processes are discussed. The electron impact absolute total and partial ionization cross sections in pyrimidine were obtained over the energy range from the respective ionization thresholds up to 150 eV.
    The European Physical Journal D 01/2012; 66(1). · 1.51 Impact Factor
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    ABSTRACT: Electronic states of tetrahydrofuran molecules were studied in the excitation energy range 5.5-10 eV using the technique of electron energy loss spectroscopy in the gas phase. Excitation from the two conformations, C(2) and C(s), of the ground state of the molecule are observed in the measured energy loss spectra. The vertical excitation energies of the (3)(n(o)3s) triplet state from the C(2) and C(s) conformations of the ground state of the molecule are determined to be 6.03 ± 0.02 and 6.25 ± 0.02 eV, respectively. The singlet-triplet energy splitting for the n(o)3s configuration is determined to be 0.31 eV. It is also found that excitation from the C(s) conformation of the ground state has a higher cross section than that from the C(2) conformation.
    The Journal of Chemical Physics 10/2011; 135(13):134317. · 3.12 Impact Factor
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    ABSTRACT: {{Photofragmentation of tetrahydrofuran molecules in the vacuum-ultraviolet region, producing excited atomic and molecular fragments, has been studied over the energy range 14-68 eV using photon-induced fluorescence spectroscopy. Excited hydrogen atoms H(n)
    Physical Review A 03/2011; 83. · 3.04 Impact Factor
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    ABSTRACT: Electron impact ionization and ionic fragmentation of tetrahydrofuran molecules in the gas phase were studied in the energy range from ionization threshold up to 150 eV using the technique of mass spectrometry. The cation mass spectra, ionization and ionic fragmentation efficiencies were measured over this energy range. Well-resolved mass peaks were detected in the mass range 10–72 amu and assigned to corresponding ionic molecular fragments. The most abundant cation in the mass spectra is at 42 amu. Appearance energies of selected ionic fragments were also determined. Possible ionic fragmentation processes are discussed.
    Journal of Physics B Atomic Molecular and Optical Physics 02/2011; 44(5):055206. · 2.03 Impact Factor
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    ABSTRACT: The threshold photoelectron spectrum of the isoxazole molecule, C3H3NO has been measured over the photon energy range 9.9eV to 30eV with the use of synchrotron radiation. In the 9.9-10.8 eV range, corresponding to photoionization from the highest occupied molecular orbital 3a”(π3), seven well resolved vibrational series have been observed and their modes are tentatively assigned. A strong adiabatic ionization, with an energy of 11.132 ± 0.003eV corresponding to the 2a’’(π2) band, has also been observed. This is followed by a single vibrational series of the vC-H stretching mode. Photoelectron bands in the energy region 13-30 eV have also been identified, some for the first time.
    Chemical Physics 02/2010; · 1.96 Impact Factor
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    ABSTRACT: The effect of incident electrons on acetic acid clusters is explored for the first time. The acetic acid clusters are formed inside liquid helium nanodroplets and both cationic and anionic products ejected into the gas phase are detected by mass spectrometry. The cation chemistry (induced by electron ionization at 100 eV) is dominated by production of protonated acetic acid (Ac) clusters, Ac(n)H(+), although some fragmentation is also observed. In the case of anion production (at 2.8 eV electron energy) there is a clear distinction between the monomer and the clusters. For the monomer the dominant product is the dehydrogenated species, [Ac-H](-), whereas for the clusters both the parent anion, Ac(n)(-), and the dehydrogenated species, [Ac(n)-H](-), have similar abundances. A particularly intriguing contrast between the monomer and cluster anions is that helium atoms are seen attached to the latter whereas no evidence of helium atom attachment is found for the monomer. This surprising observation is attributed to the formation of acyclic (head-to-tail) acetic acid clusters in helium nanodroplets, which have more favourable electronic properties for binding helium atoms. The acyclic clusters represent a local minimum on the potential energy surface and in the case of the dimer this is distinct from the cyclic isomer (the global minimum) identified in gas phase experiments.
    Physical Chemistry Chemical Physics 12/2009; 11(48):11631-7. · 3.83 Impact Factor
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    ABSTRACT: Threshold photoelectron spectra of the tetrahydrofuran (THF) molecules, C4H8O have been measured over the photon energy range 9–29 eV using synchrotron radiation. For the lowest photoelectron band at 9.3–10.5 eV, due to ionization from the oxygen atom lone-pair 9b/12a′ orbital (C2/Cs conformations), vibrational structures have been observed superimposed on a broad maximum. The resolved vibrational series have been attributed to ionization transitions from the C2 conformation of the THF molecule with an adiabatic energy of 9.427 eV. The underlying broad maximum has been assigned to ionization from the Cs conformation of the THF molecule with a vertical energy of 9.73 eV. This is the first observation of the ionization transitions from two conformations of a pseudorotating molecule. New photoelectron bands have been also identified in the photon energy region 16–26 eV.
    Chemical Physics 01/2009; 359:77-81. · 1.96 Impact Factor
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    ABSTRACT: Electron impact ionization of helium nano-droplets containing several 104 He atoms and doped with CCl4 or SF6 molecules is studied with high-mass resolution. The mass spectra show significant clustering of CCl4 molecules, less so for SF6 under our experimental conditions. Positive ion efficiency curves as a function of electron energy indicate complete immersion of the molecules inside the helium droplets in both cases. For CCl4 we observe the molecular parent cation CCl4+ that preferentially is formed via Penning ionization upon collisions with He*. In contrast, no parent cation SF6+ is seen for He droplets doped with SF6. The fragmentation patterns for both molecules embedded in He are compared with gas phase studies. Ionization via electron transfer to He+ forms highly excited ions that cannot be stabilized by the surrounding He droplet. Besides the atomic fragments F+ and Cl+ several molecular fragment cations are observed with He atoms attached.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2009; 280(1):26-31.
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    ABSTRACT: The core excitations of the furan and carbon dioxide molecules have been studied using dispersed UV-visible fluorescence spectroscopy. Balmer-alpha (Balmer-beta) emission was measured at the O 1s and C 1s (O 1s) excitations of furan, while emission due to an excited state of the neutral oxygen atom was measured at the O 1s excitations of CO(2). The excitation functions of the emission lines display both valence and Rydberg resonances, but the latter are more enhanced.
    01/2009;
  • Marcin Dampc, Mariusz Zubek
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    ABSTRACT: Dissociation and fragmentation processes that produce electronically excited atomic and molecular fragments, following electron impact excitation, have been studied in furan. The optical excitation technique has been employed over the electron incident energy range 15–95eV. Formation of excited hydrogen atoms H(n) in the n=4–10 states has been detected by observation of the Balmer series. The diatomic CH fragments are formed in the A2Δ, B2Σ− and C2Σ− electronic states and the C2 fragments in the d3Πg excited state. The appearance energies for the H(n=4) (Hβ line) and the CH(A2Δ) (A2Δ→X2Πr transition) fragments have been measured to be 20.7±0.4 and 19.0±0.3eV, respectively. Absolute emission cross sections have been also determined for the above two transitions in the electron energy range from the appearance energy thresholds up to 95eV. Possible dissociation and fragmentation processes are discussed.
    International Journal of Mass Spectrometry - INT J MASS SPECTROM. 01/2008; 277(1):52-56.
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    ABSTRACT: Absolute differential cross sections have been measured for elastic electron scattering from tetrahydrofuran in the electron impact energy from 6 to 20 eV and in a wide scattering angle range from 20° to 180°. In the measurements the magnetic-angle-changing technique has been employed to detect the backward scattering of electrons. The integral and momentum transfer cross sections for elastic scattering have been also determined through integration of the measured differential cross sections. A detailed comparison of the obtained differential cross sections has been made with the results of very recent theoretical calculations. In the measurements attention has been paid to observe negative-ion resonances predicted in these theoretical calculations.
    Phys. Rev. A. 04/2007; 75(4).
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    ABSTRACT: Vibrational excitation of tetrahydrofuran has been studied over the incident electron energy range from 5 to 14eV and over a wide range of scattering angles (20–180°). Measurement of vibrational excitation function of the CH2 stretch modes (C–H stretching) reveals three structures at 6.0, 7.9 and 10.3eV which can be attributed to the formation of negative-ion resonances. Differential and integral cross sections for vibrational excitation of the CH2 stretch modes have also been determined.
    Chemical Physics Letters 01/2007; 443(1):17-21. · 2.15 Impact Factor