An official website of the United States government
Anions formed by the perhalobenzene series C$$_6$$Cl$$_{n}$$F$$_{6-n}$$ ($n=0-6$) are studied computationally. All members of the series form both stable valence and stable non-valence anions. At the geometry of the neutral parents, only non-valence anions are bound, and the respective vertical electron affinities show values in the $20$ to $60$meV range. Valence anions show distorted non-planar structures, and one can distinguish two types of conformers. A-type conformers show puckered-ring structures and excess electrons delocalized over several C-Cl bonds [in case of C$$_6$$F$$_6^-$$, C-F bonds], while B-type conformers possess excess electrons essentially localized in a single C-Cl bond, which is accordingly strongly stretched and bent out-of-plane. For a specific anion, all conformers are close in energy (relative energies of less than $10$kJ/mol) and are connected by low-lying transition states. Accordingly, A-type and B-type conformers possess similar adiabatic electron affinities, however, their vertical detachment energies exhibit drastically different values, which should ease conformer distinction in photoelectron spectroscopy.
more »
« less
High-Level Multireference Investigations on the Electronic States in Single-Vacancy (SV) Graphene Defects Using a Pyrene-SV Model
The nonplanar character of graphene with a single carbon vacancy defect (SV) is investigated utilizing a pyrene-SV model system by way of complete active space self-consistent field theory (CASSCF) and multi-reference configuration interaction singles and doubles (MRCISD) calculations. Planar structures were optimized with both methods showing the 3B1 state as the ground state with three energetically close states within an energy range of 1 eV. These planar structures constitute saddle-points. However, upon following the out-of-plane imaginary frequency yields more stable (by 0.22 to 0.53 eV), but non-planar structures of CS symmetry. Of these, the 1A’ structure is the lowest in energy and is strongly deformed into an L-shape. Following a further out-of-plane imaginary frequency in the non-planar structures leads to the most stable, but most deformed singlet structure of C1 symmetry. In this structure a bond is formed between the carbon atom with the dangling bond and a carbon of the cyclopentadienyl ring. This bond stabilizes the structure by more than 3 eV compared to the planar 3B1 structure. Higher excited states were calculated at MR-CISD level showing a grouping of four states low in energy and higher states starting around 3 eV.
more »
« less
- Award ID(s):
- 2107923
- PAR ID:
- 10541457
- Publisher / Repository:
- ACS Publications
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry A
- Volume:
- 127
- Issue:
- 40
- ISSN:
- 1089-5639
- Page Range / eLocation ID:
- 8287 to 8296
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
The photoelectron (PE) spectra of C6F5X– (X = Cl, Br, I) and computational results on the anions and neutrals are presented and compared to previously reported results on C6F6– [McGee, C. J. J. Phys. Chem. A 2023, 127, 8556–8565.]. The spectra all exhibit broad, vibrationally unresolved detachment transitions, indicating that the equilibrium structures of the anions are significantly different from the neutrals. The PE spectrum of C6F5Cl– exhibits a parallel photoelectron angular distribution (PAD), similar to that of the previously reported C6F6– spectrum, while the PE spectra of C6F5Br– and C6F5I– have isotropic PADs, and also exhibit a prominent X– PE feature due to photodissociation of C6F5X– resulting in X– formation. Identification of the C6F5X– detachment transition origins, which is equivalent to the neutral electron affinity (EA), in all three cases is difficult, since the broadness of the detachment feature is accompanied by vanishingly small detachment cross section near the origin. Upper limits on the EAs were determined to be 1.70 eV for C6F5Cl, 2.10 eV for C6F5Br, and 2.00 eV for C6F5I, all significantly higher than the 0.76 eV upper limit determined for C6F6 with the same experiment. The broad detachment transitions are consistent with computational results, which predict very large differences between the neutral and anionic C–X (X = Cl, Br, I) bond lengths. Based on differences between the MBIS atom charges in the anions and neutrals, the excess charge in the anion is on the unique C atom and X, in contrast to the nonplanar C2v structured C6F6– anion, for which the charge is delocalized over the molecule. In C6F5Cl–, the C–Cl bond is predicted to be bent out of the plane, while both C6F5Br– and C6F5I– are predicted to be planar on average. The impact of the interruption of the symmetry in the hexafluorobenzene neutral and anion on the molecular and electronic structure of C6F5X/C6F5X– is considered, as well as the possible dissociative state leading to X– (X = Br, I) formation, and the nature of the C–X bond.more » « less
-
The stability and resonance spectra associated with a domain wall skyrmion embedded within a Néel skyrmion, forming a 1-kink skyrmion, has been studied using micromagnetic simulations. We show that the 1-kink skyrmion is stable over a wide range of fields at moderate strengths of the Dzyaloshinskii-Moriya interaction. By exciting these structures with a broadband magnetic field excitation, we find complex resonance behavior deviating from that of a pure Néel skyrmion. For out-of-plane excitations, the 1-kink skyrmion demonstrates an additional mode relative to that of the Néel skyrmion at reduced amplitude. These consist of low frequency and high frequency modes associated with both a breathing mode and an oscillation of the embedded domain wall skyrmion. Following an in-plane excitation, both Néel and 1-kink skyrmions exhibit a counterclockwise rotational mode with similar frequencies, as well as a higher frequency mode associated with the interaction of the structure with the ferromagnetic background state. These results may help pave the way for exploration of more complex spin structures for magnetic-based microwave devices.more » « less
-
Abstract Reliability of magnetic recordings of the ancient magnetic field is strongly dependent on the magnetic mineralogy of natural samples. Theoretical estimates of long‐term stability of remanence were restricted to single‐domain (SD) states, but micromagnetic models have recently demonstrated that the so‐called single‐vortex (SV) domain structure can have even higher stability that SD grains. In larger grains (10 μm in magnetite) the multidomain (MD) state dominates, so that large uniform magnetic domains are separated by narrow domain walls. In this paper we use a parallelized micromagnetic finite element model to provide resolutions of many millions of elements allowing us, for the first time, to examine the evolution of magnetic structure from a uniform state, through the SV state up to the development of the domain walls indicative of MD states. For a cuboctahedral grain of magnetite, we identify clear domain walls in grains as small as ∼3 μm with domain wall widths equal to that expected in large MD grains; we therefore put the SV to MD transition at ∼3 μm for magnetite and expect well‐defined, and stable, SV structures to be present until at least ∼1 μm when reducing the grain size. Reducing the size further shows critical dependence on the history of domain structures, particularly with SV states that transition through a so‐called “unstable zone” leading to the recently observed hard‐aligned SV states that proceed to unwind to SD yet remain hard aligned.more » « less
-
We report the experimental resonance enhanced multiphoton ionization spectrum of isoquinoline between 315 and 310 nm, along with correlated electronic structure calculations on the ground and excited states of this species. This spectral region spans the origin transitions to a π–π* excited state, which previous work has suggested to be vibronically coupled with a lower lying singlet n–π* state. Our computational results corroborate previous density functional theory calculations that predict the vertical excitation energy for the n–π* state to be higher than the π–π* state; however, we find an increase in the C–N–C angle brings the n–π* state below the energy of the π–π* state. The calculations find two out-of-plane vibrational modes of the n–π* state, which may be brought into near resonance with the π–π* state as the C–N–C bond angle increases. Therefore, the C–N–C bond angle may be important in activating vibronic coupling between the states. We fit the experimental rotational contour with a genetic algorithm to determine the excited state rotational constants and orientation of the transition dipole moment. The fits show a mostly in-plane polarized transition, and the projection of the transition dipole moment in the a-b plane is about 84° away from the a axis. These results are consistent with the prediction of our electronic structure calculations for the transition dipole moment of the π–π* excited state.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.jpca.3c04099
