“…In Figure , the frequency spectrum and hyperfine-correlation spectrum clearly shows a state with a very low hyperfine coupling in the region of 5 MHz. The fit to the time-dependent asymmetry in Figure includes terms from a strongly coupled ( A ∼ 300 MHz) radical and a weakly coupled ( A ∼ 5 MHz) radical, and the sum of these signals plus the diamagnetic fraction accounts for almost all of the expected asymmetry …”
Section: Muonium In Organic Donorsmentioning
confidence: 99%
“… 9 TF muon-spin-rotation signal for TTF in 0.2 T field at different temperatures. The solid lines show fitting to the sum of two radical muon-spin-rotation signals with hyperfine constants A 1 ∼ 300 MHz and A 2 ∼ 5 MHz, from ref . 10 Upper panel shows the frequency spectrum of the 0.2 T TF muon-spin-rotation signal in TTF close to the diamagnetic frequency (γ μ B ) at 28 MHz. Lower panel shows the corresponding radical frequency correlation spectrum, indicating a distinct state with hyperfine coupling around 5 MHz, from ref .…”
“…In Figure , the frequency spectrum and hyperfine-correlation spectrum clearly shows a state with a very low hyperfine coupling in the region of 5 MHz. The fit to the time-dependent asymmetry in Figure includes terms from a strongly coupled ( A ∼ 300 MHz) radical and a weakly coupled ( A ∼ 5 MHz) radical, and the sum of these signals plus the diamagnetic fraction accounts for almost all of the expected asymmetry …”
Section: Muonium In Organic Donorsmentioning
confidence: 99%
“… 9 TF muon-spin-rotation signal for TTF in 0.2 T field at different temperatures. The solid lines show fitting to the sum of two radical muon-spin-rotation signals with hyperfine constants A 1 ∼ 300 MHz and A 2 ∼ 5 MHz, from ref . 10 Upper panel shows the frequency spectrum of the 0.2 T TF muon-spin-rotation signal in TTF close to the diamagnetic frequency (γ μ B ) at 28 MHz. Lower panel shows the corresponding radical frequency correlation spectrum, indicating a distinct state with hyperfine coupling around 5 MHz, from ref .…”
“…In the past decade alone, the HFCCs of various muoniated radicals have been obtained and often characterized with the aid of theory in a wide variety of host media and molecular environments. [6][7][8][9][10][11][12][13] The present paper focuses on calculations of HFCCs for muoniated butyl radicals at 0 K, in part to help explain the experimental data discussed in the paper that follows, hereafter referred to as paper II. 14 To our knowledge, there have been no previous detailed and systematic ab initio calculations of the HFCCs of butyl radicals beyond the early INDO results of Krusic et al 15 and the later UHF study of Carmichael for the tert-butyl radical 16,17 and of Overill, 18 also for tert-butyl, only.…”
Section: ' Introduction and Backgroundmentioning
confidence: 99%
“…A central measurement in free radical studies, either by EPR or by μSR, is the isotropic hyperfine coupling constant (HFCC) that arises from the interaction between unpaired electrons and nuclear spins, and which provides valuable electronic structural information about the free radical under study. In the past decade alone, the HFCCs of various muoniated radicals have been obtained and often characterized with the aid of theory in a wide variety of host media and molecular environments. − The present paper focuses on calculations of HFCCs for muoniated butyl radicals at 0 K, in part to help explain the experimental data discussed in the paper that follows, hereafter referred to as paper II . To our knowledge, there have been no previous detailed and systematic ab initio calculations of the HFCCs of butyl radicals beyond the early INDO results of Krusic et al and the later UHF study of Carmichael for the tert -butyl radical , and of Overill, also for tert -butyl, only.…”
The hyperfine coupling constants (HFCCs) of all the butyl radicals that can be produced by muonium (Mu) addition to butene isomers (1- and 2-butene and isobutene) have been calculated, to compare with the experimental results for the muon and proton HFFCs for these radicals reported in paper II (Fleming, D. G.; et al. J. Phys. Chem. A 2011, 10.1021/jp109676b) that follows. The equilibrium geometries and HFCCs of these muoniated butyl radicals as well as their unsubstituted isotopomers were treated at both the spin-unrestricted MP2/EPR-III and B3LYP/EPR-III levels of theory. Comparisons with calculations carried out for the EPR-II basis set have also been made. All calculations were carried out in vacuo at 0 K only. A C-Mu bond elongation scheme that lengthens the equilibrium C-H bond by a factor of 1.076, on the basis of recent quantum calculations of the muon HFCCs of the ethyl radical, has been exploited to determine the vibrationally corrected muon HFCCs. The sensitivity of the results to small variations around this scale factor was also investigated. The computational methodology employed was "benchmarked" in comparisons with the ethyl radical, both with higher level calculations and with experiment. For the β-HFCCs of interest, compared to B3LYP, the MP2 calculations agree better with higher level theories and with experiment in the case of the eclipsed C-Mu bond and are generally deemed to be more reliable in predicting the equilibrium conformations and muon HFCCs near 0 K, in the absence of environmental effects. In some cases though, the experimental results in paper II demonstrate that environmental effects enhance the muon HFCC in the solid phase, where much better agreement with the experimental muon HFCCs near 0 K is found from B3LYP than from MP2. This seemingly better level of agreement is probably fortuitous, due to error cancellations in the DFT calculations, which appear to mimic these environmental effects. For the staggered proton HFCCs of the butyl radicals exhibiting no environmental effect in paper II, the best agreement with experiment is consistently found from the B3LYP calculations, in agreement also with benchmark calculations carried out for the ethyl radical.
“…In organic compounds, the origin of mSR spin dynamics may arise either from molecular motion or from scattering with charge carriers. The first is more usual in insulating materials [4], whereas the second is observed in conducting ones [5]. In the phthalocyanine's case, it is due to spincattering with charge-carriers, since the activation energy of the LF relaxation rate was found to be quite different from the activation energy of the hyperfine interaction shift.…”
This work reports a spectroscopic and spin-dynamics mSR study of the positive muon states formed in the phthalocyanines Zn-Pc, H 2 -Pc and Cu-Pc. In Zn-Pc and H 2 -Pc, three distinct muoniated radicals are formed, seen to undergo spin-dynamical processes with charge carriers. Two of the states have very similar hyperfine interaction values, and are believed to be due to muon addition at the outer benzene rings. The third one has a significantly lower hyperfine constant, and is tentatively assigned to addition at an inner part of the molecule. In Cu-Pc, the mSR signals found are diamagnetic-like, and the muon seems to be shielded from interactions with charge carriers and local molecular motion. r
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