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![Excitation functions of phenyl azide. Bottom: pure vibrational excitation, centre: excitation of a triplet state, top: excitation of a dipole-allowed singlet–singlet transition. Vertical bars indicate the attachment energies estimated from the virtual orbital energies using the empirical scaling relation of Chen and Gallup [27].](profile/Stefan-Grimme/publication/230918615/figure/fig1/AS:339688553500678@1457999470689/Excitation-functions-of-phenyl-azide-Bottom-pure-vibrational-excitation-centre.png)
Excitation functions of phenyl azide. Bottom: pure vibrational excitation, centre: excitation of a triplet state, top: excitation of a dipole-allowed singlet–singlet transition. Vertical bars indicate the attachment energies estimated from the virtual orbital energies using the empirical scaling relation of Chen and Gallup [27].
Source publication
Electron-induced chemistry—dissociative electron attachment (DEA)—was studied for phenyl azide. The major fragment corresponded to the loss of N2 and formation of the phenylnitrene anion. This process has an onset already at zero kinetic energy of the incident electron and is interpreted as proceeding via the A''π* electronic ground state of the ph...
Contexts in source publication
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... shape resonances, short-lived states of the anion where the incident electron is temporarily captured in an empty orbital of the target, can be determined by means of the electron transmission spectroscopy [24] or as an enhancement of the cross section for vibrational excitation of the target [11,25]. The vibrational excitation cross section is shown in figure 3 and exhibits two bands, at 0.85 and 2.6 eV. The same two bands appear also in the transmission spectrum, which we recorded, but do not show here. ...
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... useful way of estimating the energies of shape resonances in large molecules where scattering calculations are impractical is the use of the scaled Koopmans theorem [27]. This method, applied to HF 6-31G * virtual orbitals (at geometry calculated with DFT B3LYP), yields the values 0.48, 0.93, 0.99 and 2.49 eV, indicated by vertical bars in figure 3. The attachment energies estimated in this way rationalize very well the observation when it is taken into account that the threshold for vibrational excitation with E = 0.5 eV is at 0.5 eV, and the peak at the predicted energy of 0.48 eV cannot appear directly. ...
Context 3
... that the estimated lowest attachment energy of 0.48 eV refers to a vertical transition and the anion in its relaxed geometry is nearly certainly bound. The step at 4.7 eV in the lowest curve of figure 3 is more difficult to associate with a specific shape resonance, but could be a higher lying π * resonance located on the benzene ring, found at 4.8 eV in benzene [24]. ...
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... peak at 4.87 eV in the cross section for the excitation of the lowest triplet excited state is thus an indication of a core-excited resonance. The cross section in the topmost trace in figure 3 is a nearly linear function of energy and characteristic for a dipole allowed transition, in agreement with the prediction of the DFT/MRCI calculation discussed above. ...
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... onset of the first peak in the mass 26 spectrum probably coincides with the energetic threshold for the process. The next band, at 2.48 eV, corresponds doubtlessly to the shape resonance observed at 2.60 eV in the vibrational excitation spectrum in figure 3, and in the transmission spectrum. Three higher lying bands are observed at 4.68, 6.04 and 8.35 eV. ...
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... lowest band, at 4.68 eV, is energetically close to the expected position of the lowest Feshbach resonance, expected around this energy from the PE-spectrum. It is also quite close to the core-excited resonance seen at 4.87 eV in the triplet excitation cross section in figure 3, so that both assignments are possible. The assignment of the 6.04 and 8.35 eV bands is puzzling-they do not have a counterpart in the photoelectron spectrum, excluding an assignment to Feshbach resonances associated with the higher ionization energies. ...
Citations
... The plausible involvement of dissociative electron attachment pathway in the formation of NCRs from azidonucleosides could be inferred from the dissociative electron attachment (DEA) spectra of phenyl azide (Scheme 1). Studies establish that the major fragmentation pathway involves N 2 loss [77]. The treatment of 3′-thionocarbonate 16 with Bu3SnH resulted in radical-mediated elimination upon the generation of a radical at C3′ 17 to give 2′,3′-didehydro-2′,3′-dideoxy nucleoside 21 in moderate yields, but competing reduction of the azido group and hydrogenolysis of the thionocarbonate group also produced byproduct 20. ...
... The plausible involvement of dissociative electron attachment pathway in the formation of NCRs from azidonucleosides could be inferred from the dissociative electron attachment (DEA) spectra of phenyl azide (Scheme 1). Studies establish that the major fragmentation pathway involves N2 loss [77]. ...
Azido-modified nucleosides have been extensively explored as substrates for click chemistry and the metabolic labeling of DNA and RNA. These compounds are also of interest as precursors for further synthetic elaboration and as therapeutic agents. This review discusses the chemistry of azidonucleosides related to the generation of nitrogen-centered radicals (NCRs) from the azido groups that are selectively inserted into the nucleoside frame along with the subsequent chemistry and biological implications of NCRs. For instance, the critical role of the sulfinylimine radical generated during inhibition of ribonucleotide reductases by 2 ′-azido-2 ′-deoxy pyrimidine nucleotides as well as the NCRs generated from azidonucleosides by radiation-produced (prehydrated and aqueous) electrons are discussed. Regio and stereoselectivity of incorporation of an azido group ("radical arm") into the frame of nucleoside and selective generation of NCRs under reductive conditions, which often produce the same radical species that are observed upon ionization events due to radiation and/or other oxidative conditions that are emphasized. NCRs generated from nucleoside-modified precursors other than azidonucleosides are also discussed but only with the direct relation to the same/similar NCRs derived from azidonucleosides.
... Experimental EAs, EXPT and theoretical EAs are also included. negative ion production [56]. The existence of a significant peak in the low-energy electron-atom scattering cross section manifests negative ion formation as a resonance [57]. ...
Regge pole-calculated low-energy electron elastic total cross sections for multielectron atoms/fullerenes are characterised by ground, metastable and excited negative-ion formation, shape resonances and Ramsauer-Townsend minima. In this article, we demonstrate through the total cross sections for Eu, Au and At atoms and C60 fullerene the sensitivity of stable negative-ion formation to the crucial core-polarisation potential. The energy positions of the dramatically sharp resonances corresponding to the binding energies of the formed anions during the collisions agree excellently with the measured electron affinities of the atoms and C60. The sensitivity of Ramsauer-Townsend minima and shape resonances to the electronic structure and dynamics of Bk and Cf permits their first ever use as novel validation of the experimental observation that Cf is indeed a transitional element in the actinide series. Their electron affinities are also calculated.
... The width of the curves of effective yield (CEY) fragment [C6H5O]ˉ is much wider than that of the other fragment ions [BrC6H4O]ˉ, [M-Br]ˉ, [C6H5O]ˉ and [C6H5]ˉ, which indicates that in the energy range from 4.5 eV up to 8 eV, these ions are formed not only from shape resonance 5*and 6*, but also from a series of two-particle electron-excited Feshbach resonances at the energy higher 5 eV[20][21][22][23].Most likely, the absence of long-lived molecular negative ions (NIs) in the spectrum is explained by the fact that the electron affinity of the BDPE molecule does not exceed 0.5 eV even for the ...
Resonance electron attachment in a series of brominated diphenyl ethers, namely 4-bromodiphenyl ether (BDPE), 4-bromophenyl ether (BPE) and decabromodiphenyl ether (DBDE), was investigated in the gas phase by means of dissociative electron attachment spectroscopy (DEAS). In addition to channels of dissociation into stable fragments, long-lived molecular negative ions with an average lifetime relative to autodetachment of the order of 60 μs were found for the last two molecules. In the case of BDPE and BPE, the most intense dissociation channel is the bromine anion, and for DBDE-the [C6Br5O]ˉ anion. The [C6Br5O]ˉ anion sequentially decomposes with the elimination of the bromide anion on a microsecond time scale, which is confirmed by the registration of metastable ions with an apparent mass of 12.8 a.m.u.. The electron affinity of the studied molecules and the appearance energy of fragment ions were estimated with CAM-B3LYP/6-311+G(d,p). Keywords Dissociative electron attachment, long-lived anions, brominated diphenyl ether
In this work, electron-induced site-specific formation of neutral π-type aminyl radicals (RNH·) and their reactions with pyrimidine nucleoside analogs azidolabeled at various positions in the sugar moiety, e.g., at 2′-, 3′-, 4′-, and 5′- sites along with a model compound 3-azido-1-propanol (3AZPrOH), were investigated. Electron paramagnetic resonance (EPR) studies confirmed the site and mechanism of RNH· formation via dissociative electron attachment-mediated loss of N2 and subsequent facile protonation from the solvent employing the 15N-labeled azido group, deuterations at specific sites in the sugar and base, and changing the solvent from H2O to D2O. Reactions of RNH· were investigated employing EPR by warming these samples from 77 K to ca. 170 K. RNH· at a primary carbon site (5′-azido-2′,5′-dideoxyuridine, 3AZPrOH) facilely converted to a σ-type iminyl radical (R═N·) via a bimolecular H-atom abstraction forming an α-azidoalkyl radical. RNH· when at a secondary carbon site (e.g., 2′-azido-2′-deoxyuridine) underwent bimolecular electrophilic addition to the C5═C6 double bond of a proximate pyrimidine base. Finally, RNH· at tertiary alkyl carbon (4′-azidocytidine) underwent little reaction. These results show the influence of the stereochemical and electronic environment on RNH· reactivity and allow the selection of those azidonucleosides that would be most effective in augmenting cellular radiation damage.
The gas-phase acidities of chloroanilino-radicals have been measured, and have been combined with the electron affinities of chlorophenylnitrenes to determine the N–H bond dissociation energy of chloroanilino-radicals and the enthalpies of formation for the triplet, singlet, and radical anion states of the isomeric nitrenes. There is little difference found between the bond dissociation energies in the radicals and those in the corresponding anilines, indicating little interaction between the unpaired electrons in the chlorophenylnitrene, as expected. The values obtained are in good agreement with the values obtained from the theoretical calculations.
We observe two ion formation thresholds when monochromatized synchrotron radiation is tuned through the onset of the methyl azide ion-pair channel (CH3N3 + hν → CH3+ + N3–). We assign these to production of the two lowest electronic states of the azide anion: the singlet linear (1Σg+) and the triplet bent (3B2) forms of N3–. This finding is supported by extensive quantum chemical calculations on the N3– singlet and triplet potential energy surfaces. Quantum chemical calculations are also used to rule out alternative ionization channels that exhibit the same m/z ratios: NH+ + isomers of CH2N2–. A value of 292.9 kJ/mol for the D0(CH3–N3) is suggested.
The recent Regge-pole methodology, which includes the essential electron correlations, is employed together with a Thomas–Fermi type potential incorporating the vital core-polarization interaction to calculate low-energy (E less than or equal to 1 eV) electron elastic total and Mulholland cross sections for the complex atoms Nd, Eu, and Tm, found to be characterized by subtle Regge resonances, for a fundamental understanding of the mechanism of the near-threshold electron attachment. The binding energies of the complex negative ions Nd–, Eu–, and Tm– formed through the collisions as Regge resonances are extracted for the first time from the resonances and compared with the latest theoretical and experimental values. Ramsauer–Townsend minima, shape resonances, and the Wigner threshold behavior are also obtained.
Total and Mulholland partial cross sections for the elastic scattering of electrons from the lanthanide atoms lanthanum to lutetium are calculated for the electron impact energy range 0⩽E⩽1 eV. The recently developed Regge-pole methodology, which naturally embodies the crucial electron correlation effects together with a Thomas-Fermi-type potential incorporating the vital core-polarization interaction are used for the calculations. Dramatically sharp resonances are found to characterize the near-threshold electron elastic scattering total and Mulholland partial cross sections, whose energy positions are identified with the electron affinities (EA’s) of these atoms through a close scrutiny of the imaginary part of the complex angular momentum. The unambiguous extracted EA values of the lanthanide atoms vary from a low value of 0.016 eV for the Tm atom to a high value of 0.631 eV for the Pr atom; none is predicted to have a lower EA value than the former. All the negative ions of the lanthanide atoms can be classified through their binding energies (BE’s) as weakly bound negative ions (BE’s <1.0 eV), while only three qualify to be classified as tenuously bound (BE’<0.1 eV). Ramsauer-Townsend minima, shape resonances, and the Wigner threshold behavior for these lanthanides are also determined. Comparisons of the present calculated EA’s with those from various experimental measurements and other theoretical calculations are presented and discussed. In particular, our extracted EA value for the complicated open d- and f-subshell Ce atom agrees excellently with the most recently measured [ Walter et al. Phys. Rev. A 76 052702 (2007)] and calculated values, while for Nd and Eu the agreement with the latest calculated values of O’Malley and Beck Phys. Rev. A 77 012505 (2008) Phys. Rev. A 78 012510 (2008) is outstanding. These agreements give great credence to the already demonstrated predictive power of the Regge-pole methodology to extract unambiguous and reliable binding energies for tenuously bound and complicated open-shell negative ionic systems, requiring no a priori knowledge of the EA values whatsoever. This new perspective to the EA determination of atoms from low-energy electron elastic scattering resonances promises far-reaching implications for future accurate and reliable theoretical EA values, even for small molecules and clusters.
Electron attachment to the lanthanide and Hf atoms resulting in the formation of stable excited lanthanide and Hf anions as Regge resonances is explored in the near-threshold electron impact energy region, E<1.0 eV. The investigation uses the recent Regge-pole methodology wherein is embedded the electron-electron correlations together with a Thomas-Fermi–type model potential incorporating the crucial core-polarization interaction. The near-threshold electron elastic total cross sections (TCSs) for the lanthanide and Hf atoms are found to be characterized by extremely narrow resonances whose energy positions are identified with the binding energies (BEs) of the resultant anions formed during the collision as Regge resonances. The extracted BEs for excited lanthanide anions are contrasted with those of the most recently calculated electron affinities (ground state BEs). We conclude that the BEs for the Pr-, Tb-, Dy-, Ho-, Er-, and Tm- anions of O’Malley and Beck Phys. Rev. A 79 012511 (2009) are not identifiable with the electron affinities as claimed. Formation of bound excited anions is identified in the elastic TCSs of all the lanthanide atoms including Hf, except Eu and Gd. The imaginary part of the complex angular momentum L, ImL is used to distinguish between the shape resonances and the bound excited negative ions. These results challenge both experimentalists and theoreticians alike since the excited anions are very weakly bound, but mostly tenuously bound (BEs<0.1 eV). Shape resonances and Ramsauer-Townsend minima are also presented.
The recent Regge-pole methodology has been employed together with a Thomas–Fermi type potential which incorporates the vital core-polarization interaction to investigate the near-threshold electron attachment in Au and Pt as Regge resonances. The resultant stable negative ion states are found to have the discernible characteristic of very small imaginary parts of the Regge poles, which translate into long-lived resonances. The near-threshold electron elastic total cross sections are characterized by multiple resonances from which we extract the electron affinity (EA) values through the scrutiny of the imaginary part of the relevant complex angular momentum. For the Au− and Pt− negative ions the extracted binding energies of 2.262 eV and 2.163 eV, respectively are in excellent agreement with the most recently measured EA values for Au and Pt. Ramsauer–Townsend minima, shape resonances and the Wigner threshold behaviour are identified in both Au− and Pt− ions.
