Autodetachment dynamics of 2-naphthoxide and implications for astrophysical anion abundance

Ashworth, Eleanor K; Anstöter, Cate S.; Verlet, Jan R. R.; Bull, James N.

doi:10.1039/d1cp00261a

Cited by 8 publications

(11 citation statements)

References 47 publications

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“…Assuming this model, pristine PAH anions and dehydrogenated derivatives should not be present in space because they have a zero or an inadequate molecular dipole moment to support a DBS; a heteroatom (e.g., N or O) or polar functional group such as −CN (cyano) is necessary to achieve |μ| > 2.0 D. 54 Furthermore, even though the parent neutral molecule in space would exist at T ≈ 4−20 K, the internal energy of a nascent anion formed through the Sarre mechanism will be above the detachment threshold and therefore susceptible to VAD. For stable interstellar anion formation, internal conversion to the S 0 electronic state must occur more rapidly than VAD; however, no such internal conversion was observed for cryocooled phenoxide, 20 2-naphthoxide at T ≈ 300 K, 43 or Py1 − at T ≈ 300 K in this study. We propose that the lack of internal conversion to the S 0 state is due to the absence of valence-bound excited states situated below the DBS, 11,16,17,55 which can couple with the DBS through active vibrations.…”

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confidence: 68%

“…3,35,42 The valence-localized state to DBS internal conversion lifetime of τ 1 = 160 ± 20 fs is within the range of subpicosecond values determined for cluster anions (∼60 fs) 18 and a model biochromophore anion (∼600 fs), 11 although the latter involved extensive nuclear motion to induce coupling. The τ 1 value is comparable with the autodetachment lifetime for the S 1 electronic state in 2naphthoxide (T ≈ 300 K) at 130 ± 10 fs, 43 a molecule which is structurally equivalent to Py1 − minus two aromatic rings. Such an ultrafast internal conversion is affected by strong coupling between the vibrational modes of the two electronic states.…”

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confidence: 74%

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Nonadiabatic Dynamics between Valence, Nonvalence, and Continuum Electronic States in a Heteropolycyclic Aromatic Hydrocarbon

Bull

Anstöter

Stockett

et al. 2021

J. Phys. Chem. Lett.

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Internal conversion between valence-localized and dipole-bound states is thought to be a ubiquitous process in polar molecular anions, yet there is limited direct evidence. Here, photodetachment action spectroscopy and time-resolved photoelectron imaging with a heteropolycyclic aromatic hydrocarbon (hetero-PAH) anion, deprotonated 1-pyrenol, is used to demonstrate a subpicosecond (τ1 = 160 ± 20 fs) valence to dipole-bound state internal conversion following excitation of the origin transition of the first valence-localized excited state. The internal conversion dynamics are evident in the photoelectron spectra and in the photoelectron angular distributions (β2 values) as the electronic character of the excited state population changes from valence to nonvalence. The dipole-bound state subsequently decays through mode-specific vibrational autodetachment with a lifetime τ2 = 11 ± 2 ps. These internal conversion and autodetachment dynamics are likely common in molecular anions but difficult to fingerprint due to the transient existence of the dipole-bound state. Potential implications of the present excited state dynamics for interstellar hetero-PAH anion formation are discussed.

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confidence: 68%

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confidence: 74%

Nonadiabatic Dynamics between Valence, Nonvalence, and Continuum Electronic States in a Heteropolycyclic Aromatic Hydrocarbon

Bull

Anstöter

Stockett

et al. 2021

J. Phys. Chem. Lett.

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“…2D PE spectroscopy supported by computational chemistry as demonstrated here offers a route to understanding these dynamics in small PAHs. Indeed, small chemical changes to the PAH such as deprotonation, , substitutions with heteroatoms, or microsolvation can dramatically alter the resonance dynamics and electron capture probabilities. The role of microsolvation of PAHs, in particular, is likely be important from an astronomical perspective because of the incorporation of PAHs in icy grains and dust in dense molecular clouds.…”

Section: Astronomical Implicationsmentioning

confidence: 99%

Temporary Anion Resonances of Pyrene: A 2D Photoelectron Imaging and Computational Study

et al. 2021

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The low-energy electron-scattering resonances of pyrene were characterized using experimental and computational methods. Experimentally, a two-dimensional photoelectron imaging of the pyrene anion was used to probe the dynamics of resonances over the first 4 eV of the continuum. Computationally, the energies and character of the anion states were determined using equation-of-motion coupled cluster calculations, while taking specific care to avoid the collapse onto discretized continuum levels, and an application of the pairing theorem. Our results are in good agreement with the predictions of electron-scattering calculations that include an offset and with the pyrene anion absorption spectrum in a glass matrix. Taken together, we offer an assignment of the first five electronic resonances of pyrene. Some of the population in the lowest-energy 2B1u resonance was observed to decay to the ground electronic state of the anion, while all other resonances decay by a direct autodetachment. The astronomical relevance of a ground-state electron capture proceeding via a low-energy resonance in pyrene is discussed.

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“…This suggested the presence of anion excited states above the detachment threshold that were resonantly excited by the photodetachment laser. Such anion excited states, which are related to the transient resonances observed in electron loss spectroscopy, − have also been observed in the related anthracenyl anion and other similar PAHs. − …”

Section: Introductionmentioning

confidence: 73%

Anion Resonances and Photoelectron Spectroscopy of the Tetracenyl Anion

Sagan

Garand

2021

J. Phys. Chem. A

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The photoelectron spectroscopy of the tetracenyl anion using slow electron velocity-map imaging (SEVI) of cryogenically cooled ions is presented. The total photodetachment yield as a function of photon energy is used to reveal a rich manifold of anion excited states above the detachment threshold. The lowest energy anionic resonance has a sufficiently long lifetime to yield a vibrationally resolved absorption spectrum that can be directly compared with theoretical predictions. Excitation of this state mostly results in electron detachment via thermionic emission. The total photodetachment yield spectrum is used to select photon wavelengths that minimize the indirect detachment signal to allow acquisition of vibrationally resolved photoelectron spectra that can inform on the neutral tetracenyl radical. Assignment of spectral features corresponding to the ground and first excited state of the neutral 12-tetracenyl isomer is made with the aid of Franck–Condon simulations. This yields adiabatic electron affinity and term energies that differ significantly from the previously reported values. Weak features corresponding to the ground state of the minor 2-teracenyl and 1-tetracenyl isomers are also identified, which allows for the experimental determination of their electron affinities for the first time.

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Autodetachment dynamics of 2-naphthoxide and implications for astrophysical anion abundance

Abstract: The first above-threshold resonance of 2-naphthoxide decays through vibrational mode specific autodetachment with a lifetime of 130 ± 10 fs. This state is not a doorway to stable interstellar anion formation.

Cited by 8 publications

References 47 publications

Nonadiabatic Dynamics between Valence, Nonvalence, and Continuum Electronic States in a Heteropolycyclic Aromatic Hydrocarbon

Nonadiabatic Dynamics between Valence, Nonvalence, and Continuum Electronic States in a Heteropolycyclic Aromatic Hydrocarbon

Temporary Anion Resonances of Pyrene: A 2D Photoelectron Imaging and Computational Study

Anion Resonances and Photoelectron Spectroscopy of the Tetracenyl Anion

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