Dynamic role of the correlation effect revealed in the exceptionally slow autodetachment rates of the vibrational Feshbach resonances in the dipole-bound state

Kang, Do Hyung; Kim, Jinwoo; Kim, Sang Kyu

doi:10.1039/d1sc05481c

Cited by 10 publications

(17 citation statements)

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“…Recent real-time pump–probe experimental studies on the state-specific dynamics of the cryogenically cooled anions such as phenoxide and some of its analogues have revealed that the dynamic range of the DBS is quite wide especially in terms of its mode-specific lifetime. − For the phenoxide anion, for instance, the DBS prepared below the photodetachment threshold decays quite slowly with its lifetime longer than tens of nanoseconds whereas the vibrational autodetachment of DBS above the detachment threshold takes place quite rapidly with a typical lifetime of tens of picoseconds. This experimental fact suggests that the DBS may undergo the rather slow radiative or nonradiative transition to the ground or excited state of the anion when the total energy is below the electron detachment threshold.…”

Section: Introductionmentioning

confidence: 99%

Experimental Observation of the Resonant Doorways to Anion Chemistry: Dynamic Role of Dipole-Bound Feshbach Resonances in Dissociative Electron Attachment

et al. 2022

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Anion chemical dynamics of autodetachment and fragmentation mediated by the dipole-bound state (DBS) have been thoroughly investigated in a state-specific way for the first time by employing the picosecond time-resolved or the nanosecond frequency-resolved spectroscopy combined with the cryogenically cooled ion trap and velocity-map imaging techniques. For the ortho-, meta-, or para-iodophenoxide anion (o-, m-, or p-IPhO -), the C-I bond rupture giving the anionic iodide (I -) fragment occurs via the nonadiabatic transition from the DBS to the nearby valence-bound states (VBS) of the anion where the vibronic coupling into the S1 (πσ*) state (which is repulsive along the C-I bond extension coordinate) should be largely responsible. The dynamic details are governed by the isomer-specific nature of the potential energy surfaces in the vicinity of the DBS-VBS curve crossings, as manifested in the huge different chemical reactivity of o-, m-, or p-IPhO -. It is confirmed here that the C-I bond dissociation is mediated by DBS resonances, providing the foremost evidence that the metastable DBS plays the essential role as the doorway into the anion chemistry especially of the dissociative electron attachment (DEA). The fragmentation channel is dominant when it is mediated by the DBS resonances located below the electron-affinity (EA) threshold, whereas it is kinetically adjusted by the competitive autodetachment process when the DBS resonances lying above EA convey the electron to the valence orbitals. The product yield of the C-I bond cleavage is strongly mode-dependent as the rate of the concomitant autodetachment is much influenced by the characteristics of the individual vibrational modes, paving a new way of the reaction control of the anion chemistry.

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Section: Introductionmentioning

confidence: 99%

Experimental Observation of the Resonant Doorways to Anion Chemistry: Dynamic Role of Dipole-Bound Feshbach Resonances in Dissociative Electron Attachment

et al. 2022

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“…Incidentally, it has recently been found that the correlation effect may be reflected in the autodetachment dynamics. 3 Namely, the autodetachment of the 11′ 1 mode of p-bromophenoxide (p-BrPhO − ) or p-chlorophenoxide (p-ClPhO − ) has been found to be exceptionally slow, giving τ ∼ 800 or 500 ps, respectively (Figure 3). These rates are significantly slow judging from the quantitative comparison with the autodetachment rate of the 11′ 1 mode of PhO − (τ ∼ 33.5 ps) as that of p-BrPhO − or p-ClPhO − is expected to be only two times slower than that of PhO − according to the Fermi's golden rule (vide supra).…”

Section: Nature Of the Electron Binding Dynamicsmentioning

confidence: 99%

“…Although the theoretical prediction suggests that the correlation effect significantly contributes to the binding energy, , insights from the experiment could not be obtained straightforwardly because it is not plausible to sort out the contribution of the correlation effect only from the total binding energy. Incidentally, it has recently been found that the correlation effect may be reflected in the autodetachment dynamics . Namely, the autodetachment of the 11′ 1 mode of p -bromophenoxide ( p -BrPhO – ) or p -chlorophenoxide ( p -ClPhO – ) has been found to be exceptionally slow, giving τ ∼ 800 or 500 ps, respectively (Figure ).…”

Section: Autodetachment Of Dbs Qbs or Cbs: Nature Of The Electron Bin...mentioning

confidence: 99%

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State-Specific Chemical Dynamics of the Nonvalence Bound State of the Molecular Anions

et al. 2022

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Conspectus Nonvalence bound states (NBS) are anionic states where the excess electron is extremely loosely bound to the neutral core through long-range potentials. In contrast to the valence orbitals of which the electron occupancy determines the molecular structure, as well as the chemical reactivity, the nonvalence orbital is quite diffuse and located far from the neutral core. The NBS can be classified into the dipole-bound state (DBS), quadruple-bound state (QBS), or correlation-bound state (CBS) according to the nature of the electron-neutral interaction, although their interaction potentials may cooperatively contribute. The NBS is ubiquitous in nature and has the strong implications in atmospheric, interstellar, or biological chemistry. Accordingly, NBS has long been conceived to play the role of the doorway into the formation of a stable anion or dissociative electron attachment (DEA). Despite intensive and extensive studies, however, the quantum-mechanical nature of NBS is still far from being thorough understanding. Herein, we describe a new aspect of state-specific NBS-mediated chemical dynamics, which has been revealed through a series of recent studies by our group. We have employed picosecond time–resolved pump–probe spectroscopy combined with cryogenically cooled ion trap and velocity-map imaging techniques to study closed-shell anions generated by electrospray ionization. DBS vibrational Feshbach resonances are prepared by the optical excitation of phenoxide, for instance, and their individual lifetimes have been precisely measured in a state-specific manner to reveal the strong mode-dependency of the autodetachment rate. Fermi’s golden rule turns out to be extremely useful for a rational explanation of the experiment, although the more sophisticated theoretical model is desirable for the more quantitative analysis. For the DBS of para-chlorophenoxide or para-bromophenoxide where the polarizability of neutral core is substantial, the Fermi’s golden rule based on the charge-dipole potential needs to be significantly modified to include the correlation effects to explain the exceptionally slow autodetachment rates. For the QBS of 4-cyanophenoxide, the mode-specific behavior of the quadrupole ellipsoid tensor explains the strong mode-dependent autodetachment rate. Meanwhile, the nonadiabatic transition of the excess electron into the valence orbital can result in stable anion formation or immediate chemical bond rupture. In the DBS of ortho-, meta-, or para-iodophenoxide, the transformation of the loosely bound excess electron into the πσ* antibonding orbital occurs to give I– as a final fragment. The fragmentation mediated by DBS occurs competitively with the concomitant autodetachment, paving a new way of the reaction control by tuning the quantum-mechanical nature of the DBS Feshbach resonance. This experimental observation provides the foremost evidence for the dynamic role of the DBS as a doorway into anion chemistry, such as DEA. The ponderomotive force on the electron in the nonvalence orbital...

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“…In combination with cryogenic cooling of anions, DBSs have since been exploited as an important platform for obtaining vibrational information on radical species using rPES − yielding much richer spectroscopic information than conventional PES. Pump–Probe experiments have also been utilized to investigate the autodetachment dynamics from the DBS. , …”

Section: Introductionmentioning

confidence: 99%

Dipole-Bound State, Photodetachment Spectroscopy, and Resonant Photoelectron Imaging of Cryogenically-Cooled 2-Cyanopyrrolide

2022

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Valence-bound anions with polar neutral cores can have diffuse dipole-bound excited states just below the electron detachment threshold. Because of the similarity in geometry and vibrational frequencies between the dipole-bound states (DBSs) and the corresponding neutrals, DBSs have been exploited as intermediate states to conduct resonant photoelectron spectroscopy (PES), resulting in highly non-Franck−Condon photoelectron spectra via vibrational autodetachment and providing much richer vibrational information than conventional PES. Here, we report a photodetachment and high-resolution photoelectron imaging study of the 2-cyanopyrrolide anion, cooled in a cryogenic ion trap. The electron affinity of the 2-cyanopyrrolyl radical is measured to be 3.0981 ± 0.0006 eV (24 988 ± 5 cm −1 ). A DBS is observed for 2cyanopyrrolide at 240 cm −1 below its detachment threshold using photodetachment spectroscopy. Twenty-three above-threshold vibrational resonances (Feshbach resonances) of the DBS are observed. Resonant PES is conducted at each Feshbach resonance, yielding a wealth of vibrational information about the 2-cyanopyrrolyl radical. Resonant two-photon PES confirms the s-like dipolebound orbital and reveals a relatively long lifetime of the bound zero-point level of the DBS. Fundamental frequencies for 19 vibrational modes (out of a total of 24) are obtained for the cyanopyrrolyl radical, including six out-of-plane modes. The current work provides important spectroscopic information about 2-cyanopyrrolyl, which should be valuable for the study of this radical in combustion or astronomical environments.

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Dynamic role of the correlation effect revealed in the exceptionally slow autodetachment rates of the vibrational Feshbach resonances in the dipole-bound state

Abstract: Real-time autodetachment dynamics of the loosely-bound excess electron from the vibrational Feshbach resonances of the dipole-bound states (DBS) of 4-bromophonoxide (4-BrPhO-) and 4-chlorophenoxide (4-ClPhO-) anions have been thoroughly investigated. The...

Cited by 10 publications

References 46 publications

Experimental Observation of the Resonant Doorways to Anion Chemistry: Dynamic Role of Dipole-Bound Feshbach Resonances in Dissociative Electron Attachment

Experimental Observation of the Resonant Doorways to Anion Chemistry: Dynamic Role of Dipole-Bound Feshbach Resonances in Dissociative Electron Attachment

State-Specific Chemical Dynamics of the Nonvalence Bound State of the Molecular Anions

Dipole-Bound State, Photodetachment Spectroscopy, and Resonant Photoelectron Imaging of Cryogenically-Cooled 2-Cyanopyrrolide

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