Eero Itälä - Academia.edu (original) (raw)
Papers by Eero Itälä
International Journal of Mass Spectrometry, 2014
Journal of Physics B: Atomic, Molecular and Optical Physics, 2013
ABSTRACT We have studied the fragmentation of gas phase thymidine following valence and core ioni... more ABSTRACT We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses 13C labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-d-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.
The Journal of Chemical Physics
X-ray absorption commonly involves dissociative core ionization producing not only momentum corre... more X-ray absorption commonly involves dissociative core ionization producing not only momentum correlated charged fragments but also low- and high-energy electrons capable of inducing damage in living tissue. This gives a natural motivation for studying the core ionization induced fragmentation processes in biologically important molecules such as amino acids. Here the fragmentation of amino acid glycine following carbon 1s core ionization has been studied. Using photoelectron-photoion-photoion coincidence technique, a detailed analysis on fragmentation of the sample molecule into pairs of momentum correlated cations has been carried out. The main characteristics of core ionization induced fragmentation of glycine were found to be the rupture of the C-Cα bond and the presence of the [Formula: see text] fragment.
The Journal of Physical Chemistry B, 2014
A photoelectron-ion-ion coincidence experiment has been carried out on the amino acid molecule cy... more A photoelectron-ion-ion coincidence experiment has been carried out on the amino acid molecule cysteine after core-ionization of the O 1s, N 1s, C 1s, and S 2p orbitals. A number of different dissociation channels have been identified. Some of them show strong site-selective dependence that can be attributed to a combination of nuclear motion in the core-ionized state and Auger processes that populate different final electronic states in the dication.
The Journal of Physical Chemistry A, 2014
The dependence of the fragmentation of doubly charged gas-phase methionine (C 5 H 11 NO 2 S) on t... more The dependence of the fragmentation of doubly charged gas-phase methionine (C 5 H 11 NO 2 S) on the electronicstate character of the parent ion is studied experimentally by energy-resolved electron ion−ion coincidence spectroscopy. The parent dication electronic states are populated by Auger transitions following site-specific sulfur 2p core ionization. Two fragmentation channels are observed to be strongly dependent on the electronic states with vacancies in weakly bound molecular orbitals. All-electron calculations are applied to assign doubly charged final states of sulfur 2p core ionized methionine. In addition, the Car−Parrinello method is applied to model fragmentation dynamics of doubly charged methionine molecules with various initial temperatures to understand the typical characteristics of the molecular dissociation and partly to support the interpretation of experimental data. Figure 1. Simplified molecular geometry of methionine with carbon and oxygen atoms enumerated.
Journal of Physics: Conference Series, 2012
ABSTRACT Ab initio and mass-resolved fragmentation study of thermally evaporated selenium cluster... more ABSTRACT Ab initio and mass-resolved fragmentation study of thermally evaporated selenium clusters Sen induced by VUV synchrotron radiation
Journal of Physics: Conference Series, 2012
ABSTRACT Auger decay following C 1s core ionization leads to dissociating doubly ionized molecula... more ABSTRACT Auger decay following C 1s core ionization leads to dissociating doubly ionized molecular states of CO2 and CS2. Detailed dynamics of these three- and two-body processes is investigated using electron-ion multicoincidence spectroscopy and Monte-Carlo simulations of various dissociation scenarios.
Journal of Electron Spectroscopy and Related Phenomena, 2011
Ionization-site-dependent fragmentation of three cyclic biomolecules -uracil, 5-bromouracil and t... more Ionization-site-dependent fragmentation of three cyclic biomolecules -uracil, 5-bromouracil and thymine -has been studied using electron-energy-resolved photoelectronphotoion-photoion coincidence spectroscopy. Previous studies concerning ionization site dependent fragmentation have mainly been carried out with linear molecules. The results reported here show that all studied molecules have dicationic fragmentation channels whose intensity depends on the initial core-ionization site, although these channels cover only a relatively small fraction of the total fragment yield. The present study shows on one hand, that it is often the surrounding bond(s) of the ionized atom that will break following the initial core ionization, and on the other hand, that some specific fragmentation channels can display strong site-dependency where there is no direct correlation between the ionization site and the bond breakage locations.
The Journal of Chemical Physics, 2010
Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the c... more Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the core ionization by soft x-rays using photoelectron-photoion-photoion coincidence technique has been studied. The fragment ion mass spectra were recorded in coincidence with the C 1s photoelectron spectra. In the case of thymine, deuterated samples were used to identify fragments. Deuteration or bromination allowed us to study not only the main fragmentation channels of these pyrimidine bases, but also to investigate if replacement of an exocyclic functional group affects molecular fragmentation. We found that the dominant fragmentation channels involve only one starting geometry, and the base ring and other bond cleavages, leading to the detected fragments, are essentially identical between thymine and 5-bromouracil. In addition, the relative intensities of the strongest fragmentation channels were determined and compared with calculated appearance energies using ab initio unrestricted Hartree-Fock theory.
The Journal of Chemical Physics, 2009
The Journal of Chemical Physics, 2012
The electronic structure and photofragmentation in outer and inner valence regions of Se n (n ≤ 8... more The electronic structure and photofragmentation in outer and inner valence regions of Se n (n ≤ 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectronphotoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se n microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se n clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies.
International Journal of Mass Spectrometry, 2009
Dissociation of acetonitrile molecules following resonant core excitations of carbon and nitrogen... more Dissociation of acetonitrile molecules following resonant core excitations of carbon and nitrogen core electrons to the LUMO orbital was investigated using the electron-energy-resolved photoelectron–photoion coincidence (PEPICO) technique. The fragment ion mass spectra were recorded in coincidence with the resonant Auger electrons, emitted in the decay process of the core-excited states. Deuterated and 13C-substituted samples were used for fragment identification. The
International Journal of Mass Spectrometry, 2011
Photofragmentation of the uracil molecule following carbon 1s core ionization and the subsequent ... more Photofragmentation of the uracil molecule following carbon 1s core ionization and the subsequent Auger deacy has been investigated. The applied technique, photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopy allows simultaneous detection of momentum-correlated photoions together with the photoelectron and makes possible a detailed investigation of different fragmentation processes. In order to help the fragment identification, also uracil where one of the carbon atoms
Monochromatic synchrotron radiation was used to promote K -shell electrons of nitrogen and carbon... more Monochromatic synchrotron radiation was used to promote K -shell electrons of nitrogen and carbon from the cyano group (C ≡ N ) of gaseous acrylonitrile (C 2 H 3 − CN ) to the unoccupied antibonding π * C≡N orbital. Photofragmentation of acrylonitrile molecules following selective resonant core excitations of carbon and nitrogen core electrons to the π * C≡N orbital were investigated using the electron-energy-resolved photoelecton-photoion coincidence (PEPICO) technique. The fragment ion mass spectra were recorded in coincidence with the resonant Auger electrons, emitted in the decay process of the core excited states. Singly and triply deuterated samples were used for fragment identification. The results showed the initial core hole localization to be of minor importance in determining the dissociation pattern of the molecular cation. The participator and spectator Auger transitions produce entirely different fragmentation patterns and the latter indicates that complex nuclear rearrangements take place. It is suggested that the calculated kinetic energy releases are caused by the existence of metastable states, which appear with the opening of the spectator Auger channels.
The Journal of Chemical Physics, 2015
Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. ... more Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses ≤43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form. C 2015 AIP Publishing LLC. [http://dx.
International Journal of Mass Spectrometry, 2014
Journal of Physics B: Atomic, Molecular and Optical Physics, 2013
ABSTRACT We have studied the fragmentation of gas phase thymidine following valence and core ioni... more ABSTRACT We have studied the fragmentation of gas phase thymidine following valence and core ionization using synchrotron radiation, combined with electron energy and ion mass resolved detection in coincidence. To identify certain fragment masses 13C labelled thymidine was also used. We find that in large part, the photofragmentation of thymidine can be described as separated thymine and 2-deoxy-d-ribose cations. However, also the intact thymidine radical cation, formation of intact base and sugar cations from glycosidic bond cleavage and several new thymidine-specific fragments are observed after valence ionization. Conversely, at the photoionization of C 1s electrons neither parent thymidine cations nor any fragments above 55 amu were detected, and only ion pairs with small masses survive core ionization, Auger decay and the subsequent Coulomb separation of the DNA sub-unit. This demonstrates the genotoxic nature of soft x-rays which in cells induce complex clustered damage similar to those yielded by heavy particles.
The Journal of Chemical Physics
X-ray absorption commonly involves dissociative core ionization producing not only momentum corre... more X-ray absorption commonly involves dissociative core ionization producing not only momentum correlated charged fragments but also low- and high-energy electrons capable of inducing damage in living tissue. This gives a natural motivation for studying the core ionization induced fragmentation processes in biologically important molecules such as amino acids. Here the fragmentation of amino acid glycine following carbon 1s core ionization has been studied. Using photoelectron-photoion-photoion coincidence technique, a detailed analysis on fragmentation of the sample molecule into pairs of momentum correlated cations has been carried out. The main characteristics of core ionization induced fragmentation of glycine were found to be the rupture of the C-Cα bond and the presence of the [Formula: see text] fragment.
The Journal of Physical Chemistry B, 2014
A photoelectron-ion-ion coincidence experiment has been carried out on the amino acid molecule cy... more A photoelectron-ion-ion coincidence experiment has been carried out on the amino acid molecule cysteine after core-ionization of the O 1s, N 1s, C 1s, and S 2p orbitals. A number of different dissociation channels have been identified. Some of them show strong site-selective dependence that can be attributed to a combination of nuclear motion in the core-ionized state and Auger processes that populate different final electronic states in the dication.
The Journal of Physical Chemistry A, 2014
The dependence of the fragmentation of doubly charged gas-phase methionine (C 5 H 11 NO 2 S) on t... more The dependence of the fragmentation of doubly charged gas-phase methionine (C 5 H 11 NO 2 S) on the electronicstate character of the parent ion is studied experimentally by energy-resolved electron ion−ion coincidence spectroscopy. The parent dication electronic states are populated by Auger transitions following site-specific sulfur 2p core ionization. Two fragmentation channels are observed to be strongly dependent on the electronic states with vacancies in weakly bound molecular orbitals. All-electron calculations are applied to assign doubly charged final states of sulfur 2p core ionized methionine. In addition, the Car−Parrinello method is applied to model fragmentation dynamics of doubly charged methionine molecules with various initial temperatures to understand the typical characteristics of the molecular dissociation and partly to support the interpretation of experimental data. Figure 1. Simplified molecular geometry of methionine with carbon and oxygen atoms enumerated.
Journal of Physics: Conference Series, 2012
ABSTRACT Ab initio and mass-resolved fragmentation study of thermally evaporated selenium cluster... more ABSTRACT Ab initio and mass-resolved fragmentation study of thermally evaporated selenium clusters Sen induced by VUV synchrotron radiation
Journal of Physics: Conference Series, 2012
ABSTRACT Auger decay following C 1s core ionization leads to dissociating doubly ionized molecula... more ABSTRACT Auger decay following C 1s core ionization leads to dissociating doubly ionized molecular states of CO2 and CS2. Detailed dynamics of these three- and two-body processes is investigated using electron-ion multicoincidence spectroscopy and Monte-Carlo simulations of various dissociation scenarios.
Journal of Electron Spectroscopy and Related Phenomena, 2011
Ionization-site-dependent fragmentation of three cyclic biomolecules -uracil, 5-bromouracil and t... more Ionization-site-dependent fragmentation of three cyclic biomolecules -uracil, 5-bromouracil and thymine -has been studied using electron-energy-resolved photoelectronphotoion-photoion coincidence spectroscopy. Previous studies concerning ionization site dependent fragmentation have mainly been carried out with linear molecules. The results reported here show that all studied molecules have dicationic fragmentation channels whose intensity depends on the initial core-ionization site, although these channels cover only a relatively small fraction of the total fragment yield. The present study shows on one hand, that it is often the surrounding bond(s) of the ionized atom that will break following the initial core ionization, and on the other hand, that some specific fragmentation channels can display strong site-dependency where there is no direct correlation between the ionization site and the bond breakage locations.
The Journal of Chemical Physics, 2010
Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the c... more Photofragmentation of thymine and 5-bromouracil into cation and neutral fragments following the core ionization by soft x-rays using photoelectron-photoion-photoion coincidence technique has been studied. The fragment ion mass spectra were recorded in coincidence with the C 1s photoelectron spectra. In the case of thymine, deuterated samples were used to identify fragments. Deuteration or bromination allowed us to study not only the main fragmentation channels of these pyrimidine bases, but also to investigate if replacement of an exocyclic functional group affects molecular fragmentation. We found that the dominant fragmentation channels involve only one starting geometry, and the base ring and other bond cleavages, leading to the detected fragments, are essentially identical between thymine and 5-bromouracil. In addition, the relative intensities of the strongest fragmentation channels were determined and compared with calculated appearance energies using ab initio unrestricted Hartree-Fock theory.
The Journal of Chemical Physics, 2009
The Journal of Chemical Physics, 2012
The electronic structure and photofragmentation in outer and inner valence regions of Se n (n ≤ 8... more The electronic structure and photofragmentation in outer and inner valence regions of Se n (n ≤ 8) clusters produced by direct vacuum evaporation have been studied with size-selective photoelectronphotoion coincidence technique by using vacuum-ultraviolet synchrotron radiation. The experimental ionization potentials of these clusters were extracted from the partial ion yield measurements. The calculations for the possible geometrical structures of the Se n microclusters have been executed. The ionization energies of the clusters have been calculated and compared with the experimental results. In addition, theoretical fragment ion appearance energies were estimated. The dissociation energies of Se n clusters were derived from the recurrent relation between the gas phase enthalpies of the formation of corresponding cationic clusters and experimental ionization energies.
International Journal of Mass Spectrometry, 2009
Dissociation of acetonitrile molecules following resonant core excitations of carbon and nitrogen... more Dissociation of acetonitrile molecules following resonant core excitations of carbon and nitrogen core electrons to the LUMO orbital was investigated using the electron-energy-resolved photoelectron–photoion coincidence (PEPICO) technique. The fragment ion mass spectra were recorded in coincidence with the resonant Auger electrons, emitted in the decay process of the core-excited states. Deuterated and 13C-substituted samples were used for fragment identification. The
International Journal of Mass Spectrometry, 2011
Photofragmentation of the uracil molecule following carbon 1s core ionization and the subsequent ... more Photofragmentation of the uracil molecule following carbon 1s core ionization and the subsequent Auger deacy has been investigated. The applied technique, photoelectron–photoion–photoion coincidence (PEPIPICO) spectroscopy allows simultaneous detection of momentum-correlated photoions together with the photoelectron and makes possible a detailed investigation of different fragmentation processes. In order to help the fragment identification, also uracil where one of the carbon atoms
Monochromatic synchrotron radiation was used to promote K -shell electrons of nitrogen and carbon... more Monochromatic synchrotron radiation was used to promote K -shell electrons of nitrogen and carbon from the cyano group (C ≡ N ) of gaseous acrylonitrile (C 2 H 3 − CN ) to the unoccupied antibonding π * C≡N orbital. Photofragmentation of acrylonitrile molecules following selective resonant core excitations of carbon and nitrogen core electrons to the π * C≡N orbital were investigated using the electron-energy-resolved photoelecton-photoion coincidence (PEPICO) technique. The fragment ion mass spectra were recorded in coincidence with the resonant Auger electrons, emitted in the decay process of the core excited states. Singly and triply deuterated samples were used for fragment identification. The results showed the initial core hole localization to be of minor importance in determining the dissociation pattern of the molecular cation. The participator and spectator Auger transitions produce entirely different fragmentation patterns and the latter indicates that complex nuclear rearrangements take place. It is suggested that the calculated kinetic energy releases are caused by the existence of metastable states, which appear with the opening of the spectator Auger channels.
The Journal of Chemical Physics, 2015
Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. ... more Fragmentation of RNA nucleoside uridine, induced by carbon 1s core ionization, has been studied. The measurements by combined electron and ion spectroscopy have been performed in gas phase utilizing synchrotron radiation. As uridine is a combination of d-ribose and uracil, which have been studied earlier with the same method, this study also considers the effect of chemical environment and the relevant functional groups. Furthermore, since in core ionization the initial core hole is always highly localized, charge migration prior to fragmentation has been studied here. This study also demonstrates the destructive nature of core ionization as in most cases the C 1s ionization of uridine leads to concerted explosions producing only small fragments with masses ≤43 amu. In addition to fragmentation patterns, we found out that upon evaporation the sugar part of the uridine molecule attains hexagonal form. C 2015 AIP Publishing LLC. [http://dx.