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Laisheng Wang - One of the best experts on this subject based on the ideXlab platform.

  • probing the dipole bound state in the 9 phenanthrolate anion by Photodetachment spectroscopy resonant two photon photoelectron imaging and resonant photoelectron spectroscopy
    Journal of Physical Chemistry A, 2021
    Co-Authors: Daofu Yuan, Chenhui Qian, Yuan Liu, Yuerou Zhang, Laisheng Wang
    Abstract:

    Valence-bound anions with a dipolar core can support dipole-bound states (DBSs) below the electron detachment threshold. The highly diffuse DBS observed is usually of σ symmetry with an s-like orbital. Recently, a π-type DBS was observed experimentally in the 9-anthrolate anion (9AT-) and it was shown to be stabilized due to the large anisotropic polarizability of the 9AT core. To confirm the general existence of π-DBS and its structural dependence, here we report an investigation of the 9-phenanthrolate anion (9PT-), which has a different structure and lower symmetry than 9AT-. Photodetachment spectroscopy revealed a DBS 257 cm-1 below the detachment threshold of 9PT- at 19 627 cm-1 (2.4334 eV). Resonant two-photon photoelectron imaging indeed showed a π symmetry for the DBS. Similar to that observed in 9AT-, the π-DBS in 9PT- is also stabilized by the anisotropic polarizability of the 9PT core and accessed via nonadiabatic population transfer from the initially populated σ-DBS. Photodetachment spectroscopy unveiled nine above-threshold vibrational resonances of the DBS, resulting in nine highly non-Franck-Condon resonant photoelectron spectra by tuning the detachment laser to the vibrational resonances. The combination of Photodetachment spectroscopy and resonant photoelectron spectroscopy allowed frequencies for nine vibrational modes of the 9-phenathroxy radical to be measured, including the six lowest frequency bending modes.

  • Photodetachment spectroscopy and resonant photoelectron imaging of cryogenically cooled 1 pyrenolate
    Journal of Chemical Physics, 2021
    Co-Authors: Chenhui Qian, Yuerou Zhang, Daofu Yuan, Laisheng Wang
    Abstract:

    We report an investigation of the 1-pyrenolate anion (PyO−) and the 1-pyrenoxy radical (PyO) using Photodetachment spectroscopy and resonant photoelectron imaging of cryogenically cooled anions. The electron affinity of PyO is measured to be 2.4772(4) eV (19 980 ± 3 cm−1) from high-resolution photoelectron spectroscopy. Photodetachment spectroscopy reveals a dipole-bound state (DBS) for PyO− 280 cm−1 below the detachment threshold as well as a broad and intense valence excited state (shape resonance) 1077 cm−1 above the detachment threshold. The shape resonance with an excitation energy of 21 055 cm−1 is due to excitation of an electron from the highest occupied molecular orbital of PyO− to its lowest unoccupied molecular orbital in the continuum. Twenty-nine vibrational levels of the DBS are observed, including 27 above-threshold vibrational levels (vibrational Feshbach resonances). Twenty-seven resonant photoelectron spectra are obtained by tuning the detachment laser to the vibrational Feshbach resonances, resulting in highly non-Franck–Condon photoelectron spectra and rich vibrational information. In total, the frequencies of 21 vibrational modes are obtained for the PyO radical by the combination of the Photodetachment and resonant photoelectron spectroscopy, including 13 out-of-plane bending modes.

  • high resolution photoelectron imaging and Photodetachment spectroscopy of cryogenically cooled io
    Journal of Physical Chemistry A, 2020
    Co-Authors: Yongtian Wang, Chuangang Ning, Hongtao Liu, Laisheng Wang
    Abstract:

    We report a high-resolution photoelectron imaging and Photodetachment spectroscopy study of cryogenically cooled IO-. The high-resolution photoelectron spectra yield a more accurate electron affinity (EA) of 2.3805(5) eV for IO as well as a more accurate spin-orbit splitting energy between the 2Π3/2 and 2Π1/2 states of IO as 2093(5) cm-1. Photodetachment spectroscopy confirmed several excited states for the IO- anion predicted by theoretical calculations, including two valence-type excited states, the repulsive 3Π state, and a shallow bound 1Π state. More interestingly, we have observed two vibrational resonances which are proposed to be due to a dipole-induced resonant state, about 230 cm-1 above the detachment threshold of IO-.

  • Photodetachment spectroscopy and resonant photoelectron imaging of the 2 naphthoxide anion via dipole bound excited states
    Journal of Chemical Physics, 2020
    Co-Authors: Chenhui Qian, Guozhu Zhu, Yuerou Zhang, Laisheng Wang
    Abstract:

    We report a Photodetachment spectroscopy and high-resolution resonant photoelectron imaging study of cryogenically cooled 2-naphthoxide anions (C10H7O-). The Photodetachment spectrum revealed a dipole-bound state (DBS) 202(4) cm-1 below the detachment threshold and 38 resonances corresponding to the vibrational levels of the DBS. By tuning the detachment laser to these above-threshold resonances, we obtained 38 resonantly enhanced photoelectron spectra, which were highly non-Franck-Condon as a result of mode-selective vibrational autodetachment from the DBS. The resonances were assigned by comparing the resonant and non-resonant photoelectron spectra, assisted by the computed vibrational frequencies. Specifically, vibrational features with low Franck-Condon factors or from Franck-Condon-forbidden vibrational modes were significantly enhanced in the resonant photoelectron spectra, resulting in much richer spectroscopic information. The electron affinity of the 2-naphthoxy radical was measured accurately to be 19 387(4) cm-1 or 2.4037(5) eV. In addition, a total of 17 vibrational frequencies were obtained for the 2-naphthoxy radical. In particular, seven Franck-Condon-forbidden out-of-plane bending modes, including the two lowest frequency modes (ν48 at 102 cm-1 and ν47 at 171 cm-1), were observed, demonstrating the advantages of combining Photodetachment spectroscopy and resonant photoelectron spectroscopy in obtaining vibrational information for polar radical species via DBS.

  • Electron tunneling through the repulsive Coulomb barrier in Photodetachment of multiply charged anions
    2020
    Co-Authors: Xuebin Wang, Chuanfan Ding, Laisheng Wang
    Abstract:

    Abstract There exists a repulsive Coulomb barrier for electrons in multiply charged anions. Tunneling through this barrier is expected to be important in Photodetachment of MCAs. Photodetachment spectra were found to shift to lower binding energies in the tunneling regime. We present a systematic study of the tunneling effect in Photodetachment experiments on a y Ž . y Ž . series of dianions, O C CH CO n s 3-6 . The observed tunneling effect and spectral shift are explained using WKB 2 2 n 2 approximation based on a model potential with a square well at short range and a repulsive Coulomb potential at long range. q 1999 Elsevier Science B.V. All rights reserved. Ionization of a neutral atom or molecule results in an outgoing electron and a positive ion, whose longrange interaction is the Coulomb attraction. Photodetachment of a singly charged anion will produce an outgoing electron and a neutral particle, whose long-range interactions are also attractive in nature. However, Photodetachment of a multiply charged Ž . anion MCA leads to two negatively charged parti-Ž cles a free electron and a negative ion with one less . charge than the parent MCA , whose long range interactions are mainly the Coulomb repulsion. The short range binding of the electron and the long range Coulomb repulsion result in a potential barrier ) Correspondin

Robert E. Continetti - One of the best experts on this subject based on the ideXlab platform.

  • dissociative Photodetachment dynamics of the oh c2h4 anion complex
    Journal of Physical Chemistry A, 2021
    Co-Authors: Yanice Benitez, Austin J Parsons, Katharine G Lunny, Robert E. Continetti
    Abstract:

    Photoelectron-photofragment coincidence (PPC) measurements on OH-(C2H4) anions at a photon energy of 3.20 eV revealed stable and dissociative Photodetachment product channels, OH-C2H4 + e- and OH + C2H4 + e-, respectively. The main product channel observed was dissociation to the reactants (>67%), OH + C2H4 (v = 0, 1, 2) + e-, where vibrational excitation in the C-H stretching modes of the C2H4 photofragments corresponds to a minor channel. The low kinetic energy release (KER) of the dissociating fragments is consistent with weak repulsion between the OH + C2H4 reactants near the transition state as well as the partitioning of energy into rotation of the dissociation products. An impulsive model was used to account for rotational energy partitioning in the dissociative Photodetachment (DPD) process and showed good agreement with the experimental results. The low KER of the dissociating fragments and the similarities in the photoelectron spectra between stable and dissociative events support a mechanism involving the van der Waals complex formed upon Photodetachment of OH-(C2H4) as an intermediate in the dominant OH + C2H4 + e- dissociative channel.

  • Dissociative Photodetachment dynamics of the oxalate monoanion
    Physical chemistry chemical physics : PCCP, 2019
    Co-Authors: J. A. Gibbard, E. Castracane, A. J. Shin, Robert E. Continetti
    Abstract:

    The dissociative Photodetachment (DPD) dynamics of the oxalate monoanion are studied using photoelectron-photofragment coincidence (PPC) spectroscopy. Following Photodetachment of C2O4H- at 4.66 eV HOCO + CO2 products are observed, indicating the facile decarboxylation of the radical driven by the thermodynamic stability of CO2. No evidence is seen for Photodetachment to stable C2O4H or ionic photodissociation to produce HOCO-. Calculations indicate the stabilizing presence of an intramolecular hydrogen bond in the anion via the formation of a strained five-membered ring. No intramolecular hydrogen bond is predicted in the radical due to the lower charge density on the oxygen atom. The PPC spectrum is consistent with a single direct two-body DPD channel that results in fragments of similar mass and is characterized by a large kinetic energy release (KER) and a broad photoelectron spectrum. The large KER is indicative of substantial repulsion in the radical following Photodetachment. The form of the photoelectron spectrum is dominated by the bound to continuum Franck-Condon factors (BCFCF) and is suggestive of Photodetachment to a repulsive potential energy surface. A lower bound for the electron affinity of C2O4H is reported as 4 eV. BCFCF calculations allow an approximate functional form of the repulsive surface along the C-C stretch coordinate to be extracted from the experimental photoelectron spectrum. PPC spectroscopy of the deuterated analogue (C2O4D-), at higher anion beam energies is used to increase the detectability of any possible D atom products, but none are observed.

  • photoelectron photofragment coincidence spectroscopy of the dissociative Photodetachment of i2 at 258 and 266 nm
    Molecular Physics, 2019
    Co-Authors: J. A. Gibbard, Robert E. Continetti
    Abstract:

    Photoelectron-photofragment coincidence (PPC) spectroscopy is used to examine the dissociative Photodetachment (DPD) of I2− at 266 and 258 nm in a kinematically complete manner. The resonance enhan...

  • effects of vibrational excitation on the f h2o hf oh reaction dissociative Photodetachment of overtone excited f h oh
    Chemical Science, 2017
    Co-Authors: R. Otto, Jun Li, Robert E. Continetti
    Abstract:

    The reaction F + H2O → HF + OH is a four-atom system that provides an important benchmark for reaction dynamics. Hydrogen atom transfer at the transition state for this reaction is expected to exhibit a strong dependence on reactant vibrational excitation. In the present study, the vibrational effects are examined by Photodetachment of vibrationally excited F−(H2O) precursor anions using photoelectron-photofragment coincidence (PPC) spectroscopy and compared with full six-dimensional quantum dynamical calculations on ab initio potential energy surfaces. Prior to Photodetachment at hνUV = 4.80 eV, the overtone of the ionic hydrogen bond mode in the precursor F−(H2O), 2νIHB at 2885 cm−1, was excited using a tunable IR laser. Experiment and theory show that vibrational energy in the anion can be effectively carried away by the photoelectron upon a Franck–Condon Photodetachment, and also show evidence for an increase of branching into the F + H2O reactant channel. The experimental results suggest a greater role for product rotational excitation than theory. Improved potential energy surfaces and longer wavepacket propagation times would be helpful to further examine the nature of the discrepancy.

  • dissociative Photodetachment studies of cooled hoco anions revealing dissociation below the barrier to h co2
    Journal of Physical Chemistry Letters, 2010
    Co-Authors: Christopher J Johnson, Robert E. Continetti
    Abstract:

    Dissociative Photodetachment of internally cold HOCO¯ has been performed in a new cryogenically cooled photoelectron−photofragment coincidence apparatus, characterizing the HOCO potential energy surface in the Franck−Condon region determined by the anion. Three processes are observed in three distinct regions of this surface: detachment to stable HOCO, dissociative Photodetachment to OH + CO, and dissociative Photodetachment to H + CO2. Relative to earlier work on internally hot anions, the H + CO2 channel is significantly enhanced, with efficient dissociation to H + CO2 unambiguously detected below calculated barriers in the OH + CO → H + CO2 reaction. This finding shows that an important low-energy pathway exists to the exit channel in this reaction, reinforcing the need for further refinement of this important potential energy surface and providing benchmarks for further theoretical efforts.

Daniel M Neumark - One of the best experts on this subject based on the ideXlab platform.

  • probing the transition state with negative ion Photodetachment experiment and theory
    Physical Chemistry Chemical Physics, 2005
    Co-Authors: Daniel M Neumark
    Abstract:

    Experimental and theoretical results are presented on the spectroscopy of transition states and pre-reactive van der Waals wells using negative ion Photodetachment. Several benchmark reactions are discussed, including the F + H2, OH + H2, and F + OH reactions, as well as the isomerization of cyclo-octatetraene. Photoelectron spectra of clustered transtion state precursor anions are presented, which examine the effects of solvation on anion structure and transition state dynamics. Finally, new experiments on the Photodetachment of ClH2− are discussed in which the Cl·H2 van der Waals well is probed.

  • high resolution Photodetachment spectroscopy of negative ions via slow photoelectron imaging
    Journal of Chemical Physics, 2004
    Co-Authors: Andreas Osterwalder, Matthew J Nee, Jia Zhou, Daniel M Neumark
    Abstract:

    A technique for high resolution anion Photodetachment spectroscopy is presented that combines velocity map imaging and anion threshold Photodetachment. This method, slow electron velocity-map imaging, provides spectral line widths of better than 1 meV. Spectra over a substantial range of electron kinetic energies are recorded in a single image, providing a dramatic reduction of data acquisition time compared to other techniques with comparable resolution. We apply this technique to atomic iodine and the van der Waals cluster I.CO2 as test systems, and then to the prereactive Cl.D2 complex where partially resolved structure assigned to hindered rotor motion is observed.

  • excited state detachment dynamics and rotational coherences of c2 via time resolved photoelectron imaging
    Chemical Physics Letters, 2003
    Co-Authors: Arthur E Bragg, Roland Wester, Daniel M Neumark, Alison V Davis, Aster Kammrath
    Abstract:

    Abstract Time-resolved photoelectron imaging (TRPEI) is used to investigate the effect of time-evolving alignment on the photoelectron angular distribution (PAD) from anion Photodetachment. The B ← X 0 0 0 transition in C 2 − is pumped with a femtosecond laser pulse at 541 nm and probed by femtosecond Photodetachment at 264 nm. The pump pulse produces rotational coherences in the upper state that exhibit partial and full revivals, as evidenced by modulation of the PAD anisotropy moments. From these, one can extract the excited state rotational constant of C 2 − and information regarding the molecular frame PAD.

  • anion spectroscopy of uracil thymine and the amino oxo and amino hydroxy tautomers of cytosine and their water clusters
    Chemical Physics, 1998
    Co-Authors: J Schiedt, R Weinkauf, Daniel M Neumark, E W Schlag
    Abstract:

    Abstract In this work we investigate different forms of electron binding in the mass-selected and cooled nucleobases uracil, thymine and cytosine and their water clusters. In Photodetachment–photoelectron spectra of the pyrimidine nucleobases, sharp structures were found at 86±8 meV (uracil), 62±8 meV (thymine) and 85±8 meV (cytosine), which are due to Photodetachment of dipole-bound states. The Photodetachment angle dependence of these states shows mostly p-wave detachment, which confirms the predicted predominant s-character of the electronic wave function of dipole-bound states. This anisotropy of electron emission and their sharp Photodetachment structures can be taken for dipole-bound state recognition. Water attachment to the nucleobases results in positive valence-bound electron affinity, s-wave detachment and broad spectra, implying that the electron now is trapped inside the π * LUMO of the nucleobases, stabilized by the water dipole. The solvent shifts in dependence on water aggregation are linear and allow by extrapolation an estimation of the monomer electron affinities. All three pyrimidine nucleobases are estimated to have a very similar valence-bound electron affinity in the range of 0–200 meV. In nucleobase·(H 2 O) n clusters, due to the large total dipole moment, dipole-bound states also exist. Resonant excitation of these dipole-bound states with a photon of 1064 nm wavelength causes dissociation of the anion cluster, leading to monomer anions in their dipole-bound state. These monomer anions can be photodetached by a second IR photon. Whereas, for uracil and thymine, one dipole-bound state is detected, for cytosine we find two dipole-bound states (85±8, 230±8 meV) which are attributed to the dipole-bound states of the simultaneously present amino-hydroxy and amino-oxo cytosine tautomers. We also give a possible explanation why the formation of the dipole-bound state of the amino-oxo tautomer at 230 meV is improbable in the supersonic expansion.

Philippe Dugourd - One of the best experts on this subject based on the ideXlab platform.

  • electron Photodetachment from gas phase peptide dianions relation with optical absorption properties
    Journal of Physical Chemistry A, 2008
    Co-Authors: Laure Joly, Rodolphe Antoine, M Broyer, Jérôme Lemoine, Philippe Dugourd
    Abstract:

    Electron detachment from peptide dianions is studied as a function of the laser wavelength. The first step for the detachment is a resonant electronic excitation of the dianions. Electronic excitation spectra are reported for three peptides, including gramicidin. A comparative study of the detachment yield for 13 peptides was performed at 260 nm and at 220 nm. At 260 nm, the detachment yield is mainly driven by the sum of the absorption coefficients of the aromatic amino acids that are contained in the peptide. At 220 nm, no direct relation is observed between the electron photodetachement yields and the sum of absorption efficiencies. At this wavelength, the sequence and the structure of the peptide may have an influence on the Photodetachment process.

  • Electron Photodetachment dissociation of DNA anions with covalently or noncovalently bound chromophores
    Journal of the American Society for Mass Spectrometry, 2007
    Co-Authors: Valérie Gabelica, Edwin De Pauw, Thibault Tabarin, Rodolphe Antoine, Frederic Rosu, M Broyer, Philippe Dugourd
    Abstract:

    Double stranded DNA multiply charged anions coupled to chromophores were subjected to UV-Vis photoactivation in a quadrupole ion trap mass spectrometer. The chromophores included noncovalently bound minor groove binders (activated in the near UV), noncovalently bound intercalators (activated with visible light), and covalently linked fluorophores and quenchers (activated at their maximum absorption wavelength). We found that the activation of only chromophores having long fluorescence lifetimes did result in efficient electron Photodetachment from the DNA complexes. In the case of ethidium-dsDNA complex excited at 500 nm, Photodetachment is a multiphoton process. The MS^3 fragmentation of radicals produced by Photodetachment at λ = 260 nm (DNA excitation) and by Photodetachment at λ > 300 nm (chromophore excitation) were compared. The radicals keep no memory of the way they were produced. A weakly bound noncovalent ligand (m-amsacrine) allowed probing experimentally that a fraction of the electronic internal energy was converted into vibrational internal energy. This fragmentation channel was used to demonstrate that excitation of the quencher DABSYL resulted in internal conversion, unlike the fluorophore 6-FAM. Altogether, Photodetachment of the DNA complexes upon chromophore excitation can be interpreted by the following mechanism: (1) ligands with sufficiently long excited-state lifetime undergo resonant two-photon excitation to reach the level of the DNA excited states, then (2) the excited-state must be coupled to the DNA excited states for Photodetachment to occur. Our experiments also pave the way towards photodissociation probes of biomolecule conformation in the gas-phase by Förster resonance energy transfer (FRET).

  • Base-dependent electron Photodetachment from negatively charged DNA strands upon 260-nm laser irradiation
    Journal of the American Chemical Society, 2007
    Co-Authors: Valérie Gabelica, Edwin De Pauw, Thibault Tabarin, Rodolphe Antoine, Frederic Rosu, M Broyer, Catherine Kinet, Philippe Dugourd
    Abstract:

    DNA multiply charged anions stored in a quadrupole ion trap undergo one-photon electron ejection (oxidation) when subjected to laser irradiation at 260 nm (4.77 eV). Electron Photodetachment is likely a fast process, given that Photodetachment is able to compete with internal conversion or radiative relaxation to the ground state. The DNA [6-mer]3- ions studied here show a marked sequence dependence of electron Photodetachment yield. Remarkably, the Photodetachment yield (dG6 > dA6 > dC6 > dT6) is inversely correlated with the base ionization potentials (G < A < C < T). Sequences with guanine runs show increased Photodetachment yield as the number of guanine increases, in line with the fact that positive holes are the most stable in guanine runs. This correlation between Photodetachment yield and the stability of the base radical may be explained by tunneling of the electron through the repulsive Coulomb barrier. Theoretical calculations on dinucleotide monophosphates show that the HOMO and HOMO-1 orbitals are localized on the bases. The wavelength dependence of electron detachment yield was studied for dG63-. Maximum electron Photodetachment is observed in the wavelength range corresponding to base absorption (260-270 nm). This demonstrates the feasibility of gas-phase UV spectroscopy on large DNA anions. The calculations and the wavelength dependence suggest that the electron Photodetachment is initiated at the bases and not at the phosphates. This also indicates that, although direct Photodetachment could also occur, autodetachment from excited states, presumably corresponding to base excitation, is the dominant process at 260 nm. Excited-state dynamics of large DNA strands still remains largely unexplored, and photo-oxidation studies on trapped DNA multiply charged anions can help in bridging the gap between gas-phase studies on isolated bases or base pairs and solution-phase studies on full DNA strands.

  • electron Photodetachment dissociation of dna polyanions in a quadrupole ion trap mass spectrometer
    Analytical Chemistry, 2006
    Co-Authors: Valérie Gabelica, Edwin De Pauw, Thibault Tabarin, Rodolphe Antoine, Frederic Rosu, Isabelle Compagnon, M Broyer, Philippe Dugourd
    Abstract:

    We hereby explore the effects of irradiating DNA polyanions stored in a quadrupole ion trap mass spectrometer with an optical parametric oscillator laser between 250 and 285 nm. We studied DNA 6−20-mer single strands and 12-base pair double strands. In all cases, laser irradiation causes electron detachment from the multiply charged DNA anions. Electron Photodetachment efficiency directly depends on the number of guanines in the strand, and maximum efficiency is observed between 260 and 275 nm. Subsequent collision-induced dissociation (CID) of the radical anions produced by electron Photodetachment results in extensive fragmentation. In addition to neutral losses, a large number of fragments from the w, d, a•, and z• ion series are obtained, contrasting with the w and (a-base) ion series observed in regular CID. The major advantage of this technique, coined electron Photodetachment dissociation (EPD) is the absence of internal fragments, combined with good sequence coverage. EPD is therefore a highly pro...

Xuebin Wang - One of the best experts on this subject based on the ideXlab platform.

  • Electron tunneling through the repulsive Coulomb barrier in Photodetachment of multiply charged anions
    2020
    Co-Authors: Xuebin Wang, Chuanfan Ding, Laisheng Wang
    Abstract:

    Abstract There exists a repulsive Coulomb barrier for electrons in multiply charged anions. Tunneling through this barrier is expected to be important in Photodetachment of MCAs. Photodetachment spectra were found to shift to lower binding energies in the tunneling regime. We present a systematic study of the tunneling effect in Photodetachment experiments on a y Ž . y Ž . series of dianions, O C CH CO n s 3-6 . The observed tunneling effect and spectral shift are explained using WKB 2 2 n 2 approximation based on a model potential with a square well at short range and a repulsive Coulomb potential at long range. q 1999 Elsevier Science B.V. All rights reserved. Ionization of a neutral atom or molecule results in an outgoing electron and a positive ion, whose longrange interaction is the Coulomb attraction. Photodetachment of a singly charged anion will produce an outgoing electron and a neutral particle, whose long-range interactions are also attractive in nature. However, Photodetachment of a multiply charged Ž . anion MCA leads to two negatively charged parti-Ž cles a free electron and a negative ion with one less . charge than the parent MCA , whose long range interactions are mainly the Coulomb repulsion. The short range binding of the electron and the long range Coulomb repulsion result in a potential barrier ) Correspondin

  • photoelectron imaging of doubly charged anions o2c ch2 nco2 n 2 8 observation of near 0 ev electrons due to secondary dissociative autodetachment
    Journal of Physical Chemistry A, 2010
    Co-Authors: Xiaopeng Xing, Xuebin Wang, Laisheng Wang
    Abstract:

    The hallmark of multiply charged anions is the repulsive Coulomb barrier (RCB), which prevents low-energy electrons from being emitted in Photodetachment experiments. However, using photoelectron imaging, we have observed persistent near 0 eV electrons during Photodetachment of doubly charged dicarboxylate anions, (-)O(2)C(CH(2))(n)CO(2)(-) (D(n)(2-), n = 2-8). Here we show that these low-energy electron signals are well structured and are independent of the detachment photon fluxes or energies. The relative intensities of these signals are dependent on n, with maxima at n = 2, 4, and 6. These near 0 eV electrons cannot come from direct Photodetachment of the dianions and are proposed to come from decarboxylation of the product radical anions upon Photodetachment of the parent dianions [(*)O(2)C(CH(2))(n)CO(2)(-) --> CO(2) + (*)(CH(2))(n)CO(2)(-)], followed by dissociative autodetachment [(*)(CH(2))(n)CO(2)(-) --> (CH(2))(n) + CO(2) + e] or hydrogen-transfer-induced electron detachment [(*)(CH(2))(n)CO(2)(-) --> CH(2)=CH(CH(2))(n-2)CO(2)H + e]. Energetic considerations suggest that these processes are exothermic. It is further observed that solvation by one water molecule quenches the low-energy electron signals in the spectra of D(n)(2-)(H(2)O), consistent with the proposed mechanisms. These indirect dissociative autodetachment processes are expected to involve cyclic transition states for n > 2, which is in agreement with the dependence on the chain length due to the anticipated strains in the intermediate steps. The quenching of the low-energy electron signals by one water molecule demonstrates the importance of solvation on chemical reactions.

  • probing free multiply charged anions using Photodetachment photoelectron spectroscopy
    Journal of Physical Chemistry A, 2000
    Co-Authors: Laisheng Wang, Xuebin Wang
    Abstract:

    Multiply charged anions are common in the condensed phase, and their existence has been generally taken for granted. But until very recently, these species have only rarely been observed in the gas phase. A new experimental technique, using Photodetachment photoelectron spectroscopy, electrospray, and ion-trap mass spectrometry, has been developed in the author's laboratory to probe multiply charged anions in the gas phase. In this article, the principles of this technique and some of the initial results will be presented and discussed. The difference between Photodetachment of singly and multiply charged anions is emphasized. Photodetachment photoelectron spectroscopy is ideal to probe the chemical and physical properties of free multiply charged anions. Among the initial findings, the repulsive Coulomb barriers existing in multiply charged anions have been directly observed. The relationship between the intramolecular electron−electron repulsion and the potential barrier is elucidated, culminating in th...

  • electron tunneling through the repulsive coulomb barrier in Photodetachment of multiply charged anions
    Chemical Physics Letters, 1999
    Co-Authors: Xuebin Wang, Chuanfan Ding, Laisheng Wang
    Abstract:

    Abstract There exists a repulsive Coulomb barrier for electrons in multiply charged anions. Tunneling through this barrier is expected to be important in Photodetachment of MCAs. Photodetachment spectra were found to shift to lower binding energies in the tunneling regime. We present a systematic study of the tunneling effect in Photodetachment experiments on a series of dianions, − O 2 C(CH2)nCO2− (n=3–6). The observed tunneling effect and spectral shift are explained using WKB approximation based on a model potential with a square well at short range and a repulsive Coulomb potential at long range.