| 1. |
- Schael, S, et al.
(författare)
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Precision electroweak measurements on the Z resonance
- 2006
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Ingår i: Physics Reports. - : Elsevier BV. - 0370-1573 .- 1873-6270. ; 427:5-6, s. 257-454
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Forskningsöversikt (refereegranskat)abstract
- We report on the final electroweak measurements performed with data taken at the Z resonance by the experiments operating at the electron-positron colliders SLC and LEP. The data consist of 17 million Z decays accumulated by the ALEPH, DELPHI, L3 and OPAL experiments at LEP, and 600 thousand Z decays by the SLID experiment using a polarised beam at SLC. The measurements include cross-sections, forward-backward asymmetries and polarised asymmetries. The mass and width of the Z boson, m(Z) and Gamma(Z), and its couplings to fermions, for example the p parameter and the effective electroweak mixing angle for leptons, are precisely measured: m(Z) = 91.1875 +/- 0.0021 GeV, Gamma(Z) = 2.4952 +/- 0.0023 GeV, rho(l) = 1.0050 +/- 0.0010, sin(2)theta(eff)(lept) = 0.23153 +/- 0.00016. The number of light neutrino species is determined to be 2.9840 +/- 0.0082, in agreement with the three observed generations of fundamental fermions. The results are compared to the predictions of the Standard Model (SM). At the Z-pole, electroweak radiative corrections beyond the running of the QED and QCD coupling constants are observed with a significance of five standard deviations, and in agreement with the Standard Model. Of the many Z-pole measurements, the forward-backward asymmetry in b-quark production shows the largest difference with respect to its SM expectation, at the level of 2.8 standard deviations. Through radiative corrections evaluated in the framework of the Standard Model, the Z-pole data are also used to predict the mass of the top quark, m(t) = 173(+10)(+13) GeV, and the mass of the W boson, m(W) = 80.363 +/- 0.032 GeV. These indirect constraints are compared to the direct measurements, providing a stringent test of the SM. Using in addition the direct measurements of m(t) and m(W), the mass of the as yet unobserved SM Higgs boson is predicted with a relative uncertainty of about 50% and found to be less than 285 GeV at 95% confidence level. (c) 2006 Elsevier B.V. All rights reserved.
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| 2. |
- Fang, Qiu, et al.
(författare)
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Photodissociation of phosgene : Theoretical evidence for the ultrafast and synchronous concerted three-body process
- 2009
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 131:16
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Tidskriftsartikel (refereegranskat)abstract
- The potential energy surfaces for Cl2CO dissociation into CO+Cl+Cl in the lowest two electronic singlet states (S-0 and S-1) have been determined by the complete active space self-consistent field, coupled-cluster method with single and double excitations (CCSD), and equation-of-motion CCSD calculations, which are followed by direct ab initio molecular dynamics simulations to explore its photodissociation dynamics at 230 nm. It is found that the C-O stretching mode is initially excited upon irradiation and the excess internal energies are transferred to the C-Cl symmetric stretching mode within 200 fs. On average, the first and the second C-Cl bonds break completely within subsequent 60 and 100 fs, respectively. Electronic structure and dynamics calculations have thus provided a strong evidence that the photoinitiated dissociation of Cl2CO at 230 nm or shorter wavelengths is an ultrafast, adiabatic, and concerted three-body process. Since the two C-Cl bonds begin to break at the same time and the time interval between the two C-Cl bond broken fully is very short (similar to 40 fs), the photoinitiated dissociation of Cl2CO to CO+2Cl can be considered as the synchronous concerted process.
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| 3. |
- Lin, Li-Li, et al.
(författare)
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Effect of Aromatic Coupling on Electronic Transport in Bimolecular Junctions
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:32, s. 14474-14477
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Tidskriftsartikel (refereegranskat)abstract
- We have performed a systematic first-principles study on conductance-voltage characteristics of bioligo(phenylene ethynylene)-monothiol molecular junctions as recently reported by Wu et al.[Nalure Nanotech. 2008, 3, 569]. It is found that the molecular conductance is very sensitive to the vertical distance between two molecules as well as the titled angle between two molecular planes. By comparing with experimental results, key structure parameters for bimolecular junction are determined, indicating that in the experimental devices, the vertical distance between two molecules is around 0.30 mn, the two planar molecules have a cofacial arrangement, and the length of the molecular bridge is about 2.88 nm. The underlying mechanism for electron transport in these aromatically coupled bimolecular junctions has also been discussed.
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| 4. |
- Lin, Na, et al.
(författare)
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Solvent Effects on the Three-Photon Absorption of a Symmetric Charge-Transfer Molecule
- 2008
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 112, s. 4703-4710
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Tidskriftsartikel (refereegranskat)abstract
- We present a theoretical study of the solvent-induced three-photon absorption cross section of a highly conjugated fluorene derivative, performed using density functional (DFT) cubic response theory in combination with the polarizable continuum model. The applicability of the often used two-state model is examined by comparison against the full DFT response theory results. It is found that the simplified model performs poorly for the three-photon absorption properties of our symmetric charge-transfer molecule. The dielectric medium enhances the three-photon absorption cross section remarkably. The effects of solvent polarity and geometrical distortions have been carefully examined. A detailed comparison with experiment is presented.
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| 5. |
- Lin, Na, 1981-
(författare)
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Theoretical Studies on Electronic and Vibrationally Resolved Multi-Photon Absorption and Dichroism
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents time-dependent density functional theory studies on electronic and vibronically resolved linear and nonlinear optical absorption and dichroism spectra of organic molecules. Special attention has been paid to the influence of solvent environment and molecular vibrations on one-, two- and three-photon absorption and one- and two-photon circular dichroism. It is found that dielectric medium as described by polarizable continuum model can enhance remarkably three-photon absorption cross section of a highly conjugated fluorene derivative, for which the simplified two-state model is shown to be largely inadequate. Origin-invariant density functional calculations on one- and two-photon circular dichroisms of a chiral molecule confirm that the recently developed CAMB3LYP functional performs better than the popular B3LYP functional for Rydberg-states. The first experimental measurement of TPCD spectra is performed on an axial chiral system in tetrahydrofunan, where the double L-scan technique is applied. Theoretical calculations well reproduce the experimental profiles when both the electron correlation and the solvent effect are taken into account. Vibronically resolved one- and two-photon absorption spectra of charge-transfer molecules have been obtained using a Linear Coupling model, where the 'borrowing mechanism' for the so-called Herzberg-Teller contribution is analyzed in detail. It is shown that Herzberg-Teller contribution can introduce a change of sign to the chiral responses of a molecule without the involvement of different electronic states, which has important consequences for the assignment of absolute configurations of chiral molecules. Adiabatic harmonic Franck-Condon model is also applied to simulate vibronically resolved one- and two-photon circular dichroism spectra of the same chiral system, where the sign-inversion and the interference between Franck-Condon and Herzberg-Teller contributions are also observed.
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| 6. |
- Lin, Na, et al.
(författare)
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Theory for Vibrationally Resolved Two-Photon Circular Dichroism Spectra : Application to(R)-(R)-(R)-(+)-3-Methylcyclopentanone
- 2009
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Ingår i: Journal of Physical Chemistry A. - : American Chemical Society (ACS). - 1089-5639 .- 1520-5215. ; 113:16, s. 4198-4207
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Tidskriftsartikel (refereegranskat)abstract
- A harmonic adiabatic approach in combination with density functional response theory for computing twophotonvibronically resolved circular dichroism spectra of chiral molecules is presented. It includes bothFranck-Condon and Herzberg-Teller contributions and it takes fully into account frequency changes andDuschinsky effects. Model calculations have been performed for two dominant conformers of (R)-(+)-3-methylcyclopentanone in the gas phase. It is found that the Herzberg-Teller contribution can introduce asign change in two-photon circular dichroism of a single excited electronic state of a conformer. The changesurvives after Boltzmann averaging, and it might be amenable to experimental verification. Interestinginterference effects between Franck-Condon and Herzberg-Teller contributions are revealed and analyzedin detail. Results obtained within the more approximate and less computationally intensive linear couplingvibronic model are also given for comparison.
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| 7. |
- Lin, Na, et al.
(författare)
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Vibronic induced one- and two-photon absorption in a charge-transfer stilbene derivate
- 2007
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 126:244509
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Tidskriftsartikel (refereegranskat)abstract
- Both the electronic and the vibronic contributions to one- and two-photon absorption of a D-pi-D charge-transfer molecule (4-dimethylamino-4(')-methyl-trans stilbene) are studied by means of density functional response theory combined with a linear coupling model. Vibronic profiles of the first four excited states are fully explored. The dominating vibrational modes for both Franck-Condon and Herzberg-Teller contributions are identified. The Franck-Condon contribution dominates the spectra of first, second, and fourth excited states. The Herzberg-Teller contribution is on the other hand of comparable size for the third excited state, where its inclusion leads to a blueshift with respect to the vertical transition. A similar vibronic coupling behavior is found for both one- and two-photon absorptions
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| 8. |
- Lin, Na, et al.
(författare)
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Vibronically-induced change in the chiral response of molecules revealed by electronic circular dichroism spectroscopy
- 2008
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Ingår i: Chemical Physics Letters. - : Elsevier BV. - 0009-2614 .- 1873-4448. ; 464, s. 144-149
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Tidskriftsartikel (refereegranskat)abstract
- A computational study of the vibronically resolved electronic circular dichroism (ECD) spectra of R-(+)- 3-methyl-cyclopentanone, including both Franck-Condon and Herzberg-Teller contributions, shows how the latter can introduce a change of sign on the chiral response of an electronic excited state. This sign inversion within the vibronically resolved electronic band, which can be interpreted as a change of the chirality of the system, has in principle important consequences in comparisons of theoretical and experimental ECD spectra employed for the assignment of absolute configurations.
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| 9. |
- Yuesheng, Ning, et al.
(författare)
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Single molecule's conductance depending on its orientation
- 2009
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 113:1, s. 26-30
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Tidskriftsartikel (refereegranskat)abstract
- Single molecules of 1,1,2,3,4,5-hexaphenylsilole adsorbed on Cu(111) have been investigated using low-temperature scanning tunneling microscopy, scanning tunneling spectroscopy, and quantum chemistry calculations. Two adsorption states have been identified, showing distinctive tunneling conductance. The molecules can switch their states under tip influence. Theoretical calculations indicate that the two states are associated with molecules adsorbed at two 90°-rotated orientations, and the tunneling conductance is attributed to molecular orbitals that spatially bridge tip-to-substrate gap. Our findings demonstrate a decisive dependence of single-molecule conductance on the molecular orientation with respect to electrodes.
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