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1.
Ptasińska S Gschliesser D Bartl P Janik I Scheier P Denifl S 《The Journal of chemical physics》2011,135(21):214309
Gas phase studies of dissociative electron attachment to simple alkyl (CF(3)SO(3)CH(3)) and aryl (C(6)H(5)SO(3)CF(3) and CF(3)SO(3)C(6)H(4)CH(3)) triflates, model molecules of nonionic photoacid generators for modern lithographic applications, were performed. The fragmentation pathways under electron impact below 10 eV were identified by means of crossed electron-molecular beam mass spectrometry. Major dissociation channels involved C-O, S-O, or C-S bond scissions in the triflate moiety leading to the formation of triflate (OTf(-)), triflyl (Tf(-)), or sulfonate (RSO(3)(-)) anions, respectively. A resonance leading to C-O bond breakage and OTf(-) formation in alkyl triflates occurred at electron energies about 0.5 eV lower than the corresponding resonance in aryl triflates. A resonance leading to S-O bond breakage and Tf(-) formation in aryl triflates occurred surprisingly at the same electron energies as C-O bond breakage. In case of alkyl triflates S-O bond breakage required 1.4 eV higher electron energies to occur and proceeded with substantially lower yields than in aryl triflates. C-S bond scission occurred for all presently studied triflates at energies close to 3 eV. 相似文献
2.
Ptasinska S Denifl S Abedi A Scheier P Märk TD 《Analytical and bioanalytical chemistry》2003,377(7-8):1115-1119
By using a high-resolution electron energy monochromator low-energy electron attachment to gas-phase glycine (H2NCH2COOH, or G) has been studied by means of mass spectrometric detection of the product anions. In the same way as for several other biologically relevant molecules no stable parent anion was formed by free electron attachment. The largest dissociative electron attachment (DEA) cross-section, approximately 5×10–20 m2, was observed for (G–H)–+H at an electron energy of 1.25 eV. Glycine and formic acid (HCOOH) have several common features, because a precursor ion can be characterized by electron attachment to the unoccupied * orbital of the –COOH group. At higher incident electron energies several smaller fragment anions are formed. Except for H–, which could not be observed in this study, there was good agreement with an earlier investigation by Gohlke et al. 相似文献
3.
Hamann T Edtbauer A da Silva FF Denifl S Scheier P Swiderek P 《Physical chemistry chemical physics : PCCP》2011,13(26):12305-12313
Dissociative electron attachment (DEA) to gaseous formamide, HCONH(2), has been investigated in the energy range between 0 eV and 18 eV using a crossed electron/molecule beam technique. The negative ion fragments have been comprehensively monitored and assigned to molecular structures by comparison with the results for two differently deuterated derivatives, namely 1D-formamide, DCONH(2), and N,N,D-formamide, HCOND(2). The following products were observed: HCONH(-), CONH(2)(-), HCON(-), OCN(-), HCNH(-), CN(-), NH(2)(-)/O(-), NH(-), and H(-). NH(2)(-) was also separated from O(-) by using high-resolution negative ion mass spectrometry. Four resonant dissociation channels can be resolved, the strongest ones being located between 2.0 and 2.7 eV and between 6.0 and 7.0 eV. CN(-) as the most abundant fragment and HCONH(-) are the dominant products of the first of these two resonances. The most important products of the latter resonance are NH(2)(-), CN(-), H(-), CONH(2)(-), and OCN(-). It is thus found that the loss of neutral H is a site-selective process, dissociation from the N site taking place between 2.0 and 2.7 eV while dissociation from the C site occurs between 6.0 and 7.0 eV. The suitability of these reactions and thus of formamide as an agent for electron-induced surface functionalisation is discussed. 相似文献
4.
Thin films of the short single DNA strand, GCAT, in which one of the bases has been removed were bombarded with 3 to 15 eV electrons. The yield functions of the H(-), O(-) and OH(-) ions desorbed from these films exhibit a broad peak near 9 eV, which is attributed to dissociative electron attachment to the basic molecules. Whereas removal of any one of the bases considerably decreases N-glycosidic and backbone C-O bond scission, the creation of basic sites does not appreciably modify bond rupture leading to anion electron stimulated desorption. These seemingly contradictory results make it possible to propose a detailed mechanism leading to the transfer of electrons in the range 5-13 eV within DNA. 相似文献
5.
Mauracher A Denifl S Aleem A Wendt N Zappa F Cicman P Probst M Märk TD Scheier P Flosadóttir HD Ingólfsson O Illenberger E 《Physical chemistry chemical physics : PCCP》2007,9(42):5680-5685
Dissociative electron attachment to gas phase glycine generates a number of fragment ions, among them ions observed at the mass numbers 15, 16 and 26 amu. From stoichiometry they can be assigned to the chemically rather different species NH(-)/CH(3)(-)(15 amu), O(-)/NH(2)(-)(16 amu) and CN(-)/C(2)H(2)(-)(26 amu). Here we use a high resolution double focusing two sector mass spectrometer to separate these isobaric ions. It is thereby possible to unravel the decomposition reactions of the different transient negative ions formed upon resonant electron attachment to neutral glycine in the energy range 0-15 eV. We find that within the isobaric ion pairs, the individual components generally arise from resonances located at substantial different energies. The corresponding unimolecular decompositions involve complex reaction sequences including multiple bond cleavages and substantial rearrangement in the precursor ion. To support the interpretation and assignments we also use (13)C labelling of glycine at the carboxylic group. 相似文献
6.
Nitrosation of thiols and thioethers in the gas phase: A combined theoretical and experimental study
Gerbaux P Wantier P Flammang R 《Journal of the American Society for Mass Spectrometry》2004,15(3):344-355
Recent studies have demonstrated the biological importance of the interaction of nitric oxide with proteins such as cytochrome-c or hemoglobin. In particular, the possibility that the nitrosonium cation, NO(+), could reversibly bind to sulfide atom type was proposed. At pH values of biological relevance, nitrosation was proposed to occur through the action of NO(+) carriers such as nitrosothiols or nitrosamines. In this context, the gas phase chemistry of protonated nitrosothiols is studied in the present work by a combination of mass spectrometry and computational methods. 相似文献
7.
Negative ion resonance states of ammonia are accessed upon capture of electrons with energy 5.5 eV and 10.5 eV, respectively. These resonance states dissociate to produce H(-) and NH(2)(-) fragment anions via different fragmentation channels. Using the velocity slice imaging technique, we measured the angular and kinetic energy distribution of the fragment H(-) and NH(2)(-) anions with full 0-2π angular coverage across the two resonances. The scattered H(-) ions at both resonances show variation in their angular distribution as a function of the kinetic energy indicating geometric rearrangement of NH(3)(-*) ion due to internal excitations and differ from the equilibrium geometry of the neutral molecule. The second resonance at 10.5 eV shows strong forward-backward asymmetry in the scattering of H(-) and NH(2)(-) fragment ions. Based on the angular distributions of the H(-) ions, the symmetry of the resonances at 5.5 eV and 10 .5 eV are determined to be A(1) and E, respectively, within C(3v) geometry. 相似文献
8.
The processes of negative ions formation of dipeptides glycyl-glycine, glycyl-alanine and alanyl-alanine in the conditions of resonant electron capture have been studied with a help of negative ions mass spectrometry. Using a thermochemical approach, the main channels of fragment negative ions formation were found and the structure of the ions were established. The isobaric ions have been identified by the experiments with high mass resolution. The cross sections of fragment ions formation were measured. The metastable fragmentation of [M-H](-) and [M-COOH](-) ions in the energy range 4.5-7.5 eV have been found. 相似文献
9.
Huber D Beikircher M Denifl S Zappa F Matejcik S Bacher A Grill V Märk TD Scheier P 《The Journal of chemical physics》2006,125(8):084304
The dissociative electron attachment to the gas phase nucleobase adenine is studied using two different experiments. A double focusing sector field mass spectrometer is utilized for measurements requiring high mass resolution, high sensitivity, and relative ion yields for all the fragment anions and a hemispherical electron monochromator instrument for high electron energy resolution. The negative ion mass spectra are discussed at two different electron energies of 2 and 6 eV. In contrast to previous gas phase studies a number of new negative ions are discovered in the mass spectra. The ion efficiency curves for the negative ions of adenine are measured for the electron energy range from about 0 to 15 eV with an electron energy resolution of about 100 meV. The total anion yield derived via the summation of all measured fragment anions is compared with the total cross section for negative ion formation measured recently without mass spectrometry. For adenine the shape of the two cross section curves agrees well, taking into account the different electron energy resolutions; however, for thymine some peculiar differences are observed. 相似文献
10.
Sulzer P Ptasinska S Zappa F Mielewska B Milosavljevic AR Scheier P Märk TD Bald I Gohlke S Huels MA Illenberger E 《The Journal of chemical physics》2006,125(4):44304
We study dissociative electron attachment to furan (FN) (C(4)H(4)O), tetrahydrofuran (THF) (C(4)H(8)O), and fructose (FRU) (C(6)H(12)O(6)) using crossed electron/molecular beams experiments with mass spectrometric detection of the anions. We find that FN and THF are weak electron scavengers and subjected to dissociative electron attachment essentially in the energy range above 5.5 eV via core excited resonances. In striking contrast to that, FRU is very sensitive towards low energy electrons generating a variety of fragment ions via a pronounced low energy feature close to 0 eV. These reactions are associated with the degradation of the ring structure and demonstrate that THF cannot be used as surrogate to model deoxyribose in DNA with respect to the attack of electrons at subexcitation energies (<3 eV). The results support the picture that in DNA the sugar moiety itself is an active part in the initial molecular processes leading to single strand breaks. 相似文献
11.
Dissociative electron attachment to SO2, NO2, NF3 and H2O2 is studied in terms of the kinetic energies of the dominant fragment ions. The O? data from SO2 show that the two major resonances at 4.6 and 7.2 eV respectively have the same dissociation limit. Similarly, the resonances at 1.8 and 3.5 eV in the O? channel in NO2 appear to have same dissociation limit of NO (X 2Π) + O?, while the resonance at 8.5 eV appears to dissociate to give NO (a 4Πi) along with O?. We find considerable internal excitation of the neutral fragments in all these cases along with that of NF3, whereas the negative ion resonance in H2O2 appears to fragment almost like a diatomic system with very little internal excitation of the OH and OH? fragments. 相似文献
12.
The photoionization and dissociative photoionization mechanism of 1,8-dihydroxyanthraquinone (1,8-DHAQ) have been investigated by infrared laser desorption/tunable synchrotron vacuum ultraviolet photoionization mass spectrometry (IR LD/VUV PIMS) technique and theoretical calculations. Consecutive losses of two carbon monoxides and elimination of hydroxyl group are found to be the major fragmentation channels in low photon energy range. Photoionization efficiency (PIE) spectrum of 1,8-DHAQ was measured in the photon energy range of 8.2-15.0 eV. Adiabatic ionization energy (IE) of 1,8-DAHQ (M) and appearance energies (AEs) of the major fragments (M-CO) (+), (M-C 2O 2) (+), and (M-OH) (+) are determined to be 8.54 +/- 0.05, 10.8 +/- 0.1, 11.0 +/- 0.1, and 13.1 +/- 0.1 eV, respectively, which are in fair agreement with calculated results. The B3LYP method with the 6-31+G(d) basis set was used to study fragmentation of 1,8-DHAQ. Theoretical calculations indicate that five lowest-energy isomers of 1,8-DHAQ cations can coexist by virtue of bond rotation and intramolecular proton transfer. A number of decarbonylation and dehydroxylation processes of 1,8-DHAQ cations are well established. 相似文献
13.
The gas-phase dissociative electron attachment spectra of di-tert-butylperoxide (DBP) and the antimalarial polycyclic peroxides artemisinin and beta-artemether are presented for the first time. The total anion currents measured at the walls of the collision chamber and the mass selected anion currents are reported in the 0-6 eV energy range. Electron attachment to DBP produces an intense current, peaking at 1.3 eV, due to the C4H9O- negative fragment, in line with the strongly O-O antibonding character of the singly occupied orbital of the parent molecular anion and the small (if any) thermodynamic energy threshold predicted by B3LYP calculations for the formation of this anion fragment. A five times less intense signal, with m/e = 57 and a maximum at 0.7 eV, is also observed. The calculations exclude that this signal can be associated with the C4H9- negative fragment, whereas they support its assignment to the C3H5O- species, generated by simultaneous dissociation and loss of a methane molecule from the parent molecular anion. In DBP, artemisinin, and beta-artemether, currents corresponding to the parent molecular anion are not detected, indicating that its survival time is shorter than the time required (about 10-6 s) to pass through the mass filter. In the latter two compounds, where simple O-O bond breaking does not generate separate fragments, the anion currents are much weaker than in DBP and the maximum total anion current peaks at zero energy. 相似文献
14.
15.
Nandi D Prabhudesai VS Nestmann BM Krishnakumar E 《Physical chemistry chemical physics : PCCP》2011,13(4):1542-1551
An experimental and theoretical investigation of the dissociative electron attachment process in nitric oxide is presented. Measurements using the recently developed ion momentum imaging conclusively show the presence of two resonance features in the O(-) channel. These are found to dissociate to give N atoms in the (2)D and (2)P excited states respectively, thus settling the controversies regarding the possible dissociation limits of this process. Though the angular distribution of O(-) shows the resonances contributing to these dissociations are of Π symmetry and a mixture of Π and Σ or Δ symmetry respectively, our calculations using R-matrix theory show no direct electron attachment channel leading to O(-) through these resonances, as all the allowed resonances below 10 eV decay to either O + N(-) or O(-) + N((4)S) channels. We propose that indirect mechanisms through curve crossings lead to the experimentally observed results. 相似文献
16.
We report a new experimental method for measuring relatively small differences in electron tunneling through two distinct monolayers. We place them side by side using scanning probe nanolithography and compare the tunneling currents by conductive probe atomic force microscopy under identical force, voltage, and tip contamination conditions. We demonstrate the validity of our approach by applying it to two isomeric molecules with similar length and functional groups, with only the position of two functional groups, one aromatic and the other aliphatic, being inverted with respect to each other. The relative values of the two tunneling currents, calculated using density functional theory and the Tersoff-Hamann approach, compare very well with the experimental data, providing us with an example of theory vs experiment agreement that is rather uncommon in this field. 相似文献
17.
Leyva V Corral I Schmierer T Heinz B Feixas F Migani A Blancafort L Gilch P González L 《The journal of physical chemistry. A》2008,112(23):5046-5053
The experimental UV/vis absorption spectrum of ortho-nitrobenzaldehyde (o-NBA) has been assigned by means of MS-CASPT2/CASSCF, TD-DFT, and RI-CC2 theoretical computations. Additional information on the nature of the absorbing bands was obtained by comparing the o-NBA spectrum with that of related compounds, as, e.g., nitrobenzene and benzaldehyde. For wavelengths larger than approximately 280 nm, the absorption spectrum of o-NBA is dominated by a series of weak n pi* absorptions from the NO2 and CHO groups. These weak transitions are followed in energy by a more intense band, peaking at 250 nm and arising from charge transfer pi pi* excitations involving mainly benzene and nitro orbitals. Finally, the most intense band centered at 220 nm has its origin in the overlap of two different absorptions: the first one localized in the NO2 substituent and the second one arising from a charge transfer excitation involving the NO2 and the CHO fragments, respectively. 相似文献
18.
Ribagnac P Blug M Villa-Uribe J Le Goff XF Gosmini C Mézailles N 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(51):14389-14393
An air-stable, bulky electron-accepting phosphine ligand (phosphabarrelene) allows the easy reduction of a Pd(II) precursor to a Pd(0) complex, highly active in room-temperature Negishi-type cross-coupling. DFT calculations show that the use of the electron-accepting ligand favors both transmetalation (TM) and reductive-elimination (RE) processes (see scheme; OA = oxidative addition). 相似文献
19.
Fang W Gong L Zhang Q Shan X Liu F Wang Z Sheng L 《The Journal of chemical physics》2011,134(17):174306
The vacuum-ultraviolet photoionization and dissociative photoionization of 1,3-butadiene in a region ~8.5-17 eV have been investigated with time-of-flight photoionization mass spectrometry using tunable synchrotron radiation. The adiabatic ionization energy of 1,3-butadiene and appearance energies for its fragment ions, C(4)H(5)(+), C(4)H(4)(+), C(4)H(3)(+), C(3)H(3)(+), C(2)H(4)(+), C(2)H(3)(+), and C(2)H(2)(+), are determined to be 9.09, 11.72, 13.11, 15.20, 11.50, 12.44, 15.15, and 15.14 eV, respectively, by measurements of photoionization efficiency spectra. Ab initio molecular orbital calculations have been performed to investigate the reaction mechanism of dissociative photoionization of 1,3-butadiene. On the basis of experimental and theoretical results, seven dissociative photoionization channels are proposed: C(4)H(5)(+) + H, C(4)H(4)(+) + H(2), C(4)H(3)(+) + H(2) + H, C(3)H(3)(+) + CH(3), C(2)H(4)(+) + C(2)H(2), C(2)H(3)(+) + C(2)H(2) + H, and C(2)H(2)(+) + C(2)H(2) + H(2). Channel C(3)H(3)(+) + CH(3) is found to be the dominant one, followed by C(4)H(5)(+) + H and C(2)H(4)(+) + C(2)H(2). The majority of these channels occur via isomerization prior to dissociation. Transition structures and intermediates for those isomerization processes were also determined. 相似文献
20.
Cicman P Buchanan GA Marston G Gulejová B Skalný JD Mason NJ Scheier P Märk TD 《The Journal of chemical physics》2004,121(20):9891-9897
Electron attachment was studied in gaseous dinitrogen pentoxide, N(2)O(5), for incident electron energies between a few meV and 10 eV. No stable parent anion N(2)O(5) (-) was observed but several anionic fragments (NO(3) (-), NO(2) (-), NO(-), O(-), and O(2) (-)) were detected using quadrupole mass spectrometry. Many of these dissociative pathways were found to be coupled and provide detailed information on the dynamics of N(2)O(5) fragmentation. Estimates of the cross sections for production of each of the anionic fragments were made and suggest that electron attachment to N(2)O(5) is amongst the most efficient attachment reactions recorded for nonhalogenated polyatomic systems. 相似文献