Photoelectron imaging: an experimental window into electronic structure

Mabbs, Richard; Grumbling, Emily R.; Pichugin, Kostyantyn; Sanov, Andrei

doi:10.1039/b815748k

Cited by 80 publications

(88 citation statements)

References 25 publications

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“…4, have nodal structure analogous to that of an atomic g orbital, in which the orbital angular momentum of the electron is l = 4. In a one-photon, one-electron process, a photoelectron is detached from an atomic orbital with Δl = ±1 (43). By extension, after detachment to form the anthracenyl e A state, the outgoing photoelectron must have at least l = 3, which yields vanishing σ at small eKE according to Eq.…”

Section: Resultsmentioning

confidence: 99%

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

Weichman

DeVine

Levine

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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Polycyclic aromatic hydrocarbons, in various charge and protonation states, are key compounds relevant to combustion chemistry and astrochemistry. Here, we probe the vibrational and electronic spectroscopy of gas-phase 9-, 1-, and 2-anthracenyl radicals (C 14 H 9 ) by photodetachment of the corresponding cryogenically cooled anions via slow photoelectron velocity-map imaging (cryo-SEVI). The use of a newly designed velocity-map imaging lens in combination with ion cooling yields photoelectron spectra with <2 cm −1 resolution. Isomer selection of the anions is achieved using gasphase synthesis techniques, resulting in observation and interpretation of detailed vibronic structure of the ground and lowest excited states for the three anthracenyl radical isomers. The groundstate bands yield electron affinities and vibrational frequencies for several Franck-Condon active modes of the 9-, 1-, and 2-anthracenyl radicals; term energies of the first excited states of these species are also measured. Spectra are interpreted through comparison with ab initio quantum chemistry calculations, Franck-Condon simulations, and calculations of threshold photodetachment cross sections and anisotropies. Experimental measures of the subtle differences in energetics and relative stabilities of these radical isomers are of interest from the perspective of fundamental physical organic chemistry and aid in understanding their behavior and reactivity in interstellar and combustion environments. Additionally, spectroscopic characterization of these species in the laboratory is essential for their potential identification in astrochemical data.polycyclic aromatic hydrocarbons | anion photoelectron spectroscopy | velocity-map imaging | vibronic structure P olycyclic aromatic hydrocarbons (PAHs) are an important class of species in many areas of chemistry. They are major components in coal (1) and in soot formed from combustion of organic matter (2, 3). PAHs are therefore common environmental pollutants and have well-documented mutagenic and carcinogenic biological activity (4, 5). PAHs are also believed to be abundant in the interstellar medium (6) and may be carriers of the anomalous IR emission bands (7-9). Recent molecular beam studies indicate that PAH growth can proceed through cold collisions of smaller hydrocarbons under interstellar conditions (10, 11). Individual PAH molecules can subsequently provide nucleation sites for amorphous graphitic grains (9). Interstellar PAHs and their clusters therefore bridge the gap between small carbonaceous molecules and larger particles, analogous to their role in soot condensation in combustion environments (12).In space, PAH species are likely to exist as an equilibrium of neutral and ionic charge states, with varying degrees of hydrogenation and dehydrogenation (13-15). Models of dense interstellar clouds find that anionic PAHs are the major carriers of negative charge, rather than free electrons (16). Closed-shell, singly deprotonated PAH carbanions have large electron affinities compared with ...

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Section: Resultsmentioning

confidence: 99%

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

Weichman

DeVine

Levine

et al. 2016

Proc. Natl. Acad. Sci. U.S.A.

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“…͑2͒ is the interference of the two partial electron waves, which of course depends on the relative cross sections ͑carried through the A · E term͒ and their relative phase shift, ␦ ͑ᐉ+1͒−͑ᐉ−1͒ . 8 …”

Section: Discussionmentioning

confidence: 99%

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

Duzor

Mbaiwa

Wei

et al. 2010

The Journal of Chemical Physics

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The ZCC model invokes vibrational channel specific "detachment orbitals" and attributes this behavior to coupling of the electronic and nuclear motion in the parent anion. The spatial extent of the model detachment orbital is dependent on the final state of O 2 : the higher the neutral vibrational excitation, the larger the electron binding energy. Although vibronic coupling is ignored in most theoretical treatments of PADs in the direct photodetachment of molecular anions, the present findings clearly show that it can be important. These results represent a benchmark data set for a relatively simple system, upon which to base rigorous tests of more sophisticated models.

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“…We find β < 0 for all transitions, consistent with electron detachment from the b 1 molecular orbital of S 3 − . 42 Peak positions and assignments (see below) are summarized in Table 1. Calculated geometries, frequencies, and the EA are listed in Table 2, along with experimental values obtained here.…”

Section: ■ Calculationsmentioning

confidence: 99%

Slow photoelectron velocity-map imaging spectroscopy of cold negative ions

Hock

Kim

Weichman

et al. 2012

The Journal of Chemical Physics

120

139

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We report high-resolution anion photoelectron spectra of thiozonide (S 3 − ) acquired by slow electron velocity-map imaging (SEVI). The ions were cryogenically cooled within an ion trap before photodetachment. We measure an electron affinity of 2.3630(9) eV, resolving discrepancies in previously reported photoelectron spectra that resulted from the presence of vibrational hot bands. The SEVI spectrum shows well-resolved, extended vibrational progressions in the symmetric stretch and bending modes of S 3 , yielding accurate frequencies for both. ■ INTRODUCTIONWith the possible exception of carbon, sulfur has more complex allotropy than any other element. 1 In addition to the numerous cyclic and polymeric forms in the solid and liquid phases, sulfur vapor is composed of the species S n (2 ≤ n ≤ 8), with trace amounts of S 9 and S 10 . 2 Aside from the diatomic S 2 , S 3 has received the most attention of these species. Its relatively small size makes it accessible to experiment and theory, and additional interest comes about because S 3 is isovalent with ozone. It has been studied by rare gas matrix IR and UV−vis spectroscopy, 3,4 resonance Raman in the gas phase, 5,6 microwave spectroscopy, 7,8 photoionization, 9 and gas-phase absorption. 10 Ab initio calculations on S 3 have focused on the question of whether the cyclic D 3h or the bent C 2v structure is the lowestenergy isomer, 11−14 finding overall agreement with experiment that the C 2v form is the stable form. High-level calculations on the structure, vibrations, and excited states of S 3 have recently been reported by Francisco et al. 15,16 In contrast to neutral S 3 , work on the S 3 − anion has largely been limited to spectroscopy in condensed phases, where it has been studied by electron paramagnetic resonance (EPR), Raman, and absorption spectroscopy. 17−19 As it is the chromophore in ultramarine pigment, 20 many of these investigations were focused on determining the properties of S 3 − in a perturbative mineral matrix or in solution. In addition, electronic absorption spectra have been measured in a cryogenic rare gas matrix. 21 Recently, the anion has been identified as the dominant form of sulfur in certain highpressure and temperature conditions approximating crustal and subduction-zone geologic fluids. 22 The new findings suggest that S 3 − may play an important role in the transport of sulfur and chalcophile metals in the earth.The neutral ← anion transition has been studied by anion photoelectron spectroscopy (PES) with resolution sufficient to resolve a progression of the ν 1 symmetric stretch. 23−25 However, the two previous studies disagreed over which peak in this progression was the vibrational origin. By assuming the anions were at the ground vibrational state, Nimlos et al. 23 obtained an electron affinity (EA) of 2.106(23) eV. Hunsicker et al. 24 found a different onset for the band, suggesting the possibility that the two experiments produced anions with different vibrational temperatures and that some of the low binding en...

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Photoelectron imaging: an experimental window into electronic structure

Cited by 80 publications

References 25 publications

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

Isomer-specific vibronic structure of the 9-, 1-, and 2-anthracenyl radicals via slow photoelectron velocity-map imaging

Vibronic coupling in the superoxide anion: The vibrational dependence of the photoelectron angular distribution

Slow photoelectron velocity-map imaging spectroscopy of cold negative ions

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