Search results for "Singlet"
showing 10 items of 352 documents
Ab initio calculations of zero-field splitting parameters in linear polyacenes
2003
Abstract The results of ab initio calculations of zero-field splitting (ZFS) parameters are presented for the linear polyacenes from benzene to pentacene. We show how the electron spin–spin (SS) parameters can be efficiently obtained from restricted high-spin open-shell wave functions (ROHF), and present calculations of these, comparing with the results of a recent multi-configurational self-consistent field approach. The SS parameters are obtained from electron SS coupling strengths evaluated as expectation values over the wave functions and from state-to-state spin–orbit (SO) interactions. The results for the two lowest triplet states of naphthalene demonstrate that excellent values can b…
Fourier-transform spectroscopy and coupled-channels deperturbation treatment of theA 1Σ+–b 3Πcomplex of KCs
2010
The laser-induced fluorescence (LIF) A {sup 1{Sigma}+}-b {sup 3{Pi}{yields}}X {sup 1{Sigma}+} spectra of the KCs molecule were recorded in a near infrared region by a Fourier-transform spectrometer with a resolution of 0.03 cm{sup -1}. Overall more than 200 collisionally enhanced LIF spectra were rotationally assigned to {sup 39}K{sup 133}Cs and {sup 41}K{sup 133}Cs isotopomers yielding more than 3400 rovibronic term values of the strongly mixed singlet A {sup 1{Sigma}+} and triplet b {sup 3{Pi}} states with the uncertainty of 0.003-0.01 cm{sup -1}. Experimental data massive starts from the lowest vibrational level v{sub A}=0 of the singlet and nonuniformly covers the energy range E is an e…
Search for a lightCP-odd Higgs boson in radiative decays ofJ/ψ
2016
We search for a light Higgs boson A(0) in the fully reconstructed decay chain of J/psi -> gamma A(0), A(0)-> mu(+)mu(-) using (225.0 +/- 2.8) x 10(6) J/psi events collected by the BESIII experiment. The A(0) is a hypothetical CP-odd light Higgs boson predicted by many extensions of the Standard Model including two spin-0 doublets plus an extra singlet. We find no evidence for A(0) production and set 90% confidence-level upper limits on the product branching fraction B(J/psi -> gamma A(0)) x B(A(0)-> mu(+)mu(-)) in the range of (2.8-495.3) x 10(-8) for 0.212 <= mA(0) <= 3.0 GeV/c(2). The new limits are five times below our previous results, and the nature of the A(0) is constrained to be mos…
A Theoretical Insight into the Photophysics of Acridine
2001
The electronic absorption and emission spectra of acridine have been studied by means of a multiconfigurational second-order perturbation method (CASSCF/CASPT2) and its multistate extension (MS-CASPT2). The low-lying valence singlet and triplet π → π* and n → π* excited states have been computed. The location of the lowest Rydberg state (3s) has been also estimated. By optimization of the geometries of the ground and low-lying excited states and the calculation of transition energies and properties, the obtained results lead to a complete analysis and assignment of the available experimental singlet−singlet and triplet−triplet absorption spectra and to the description of the basic features …
X‐ray Absorption Spectra of Cu II and Cu III Complexes of N , N ′ ‐1,2‐Phenylenebis(2‐mercapto‐2‐methylpropionamide)
2005
The X-ray absorption spectra of Cu I I and Cult complexes of N,N'-1,2-phenylenebis(2-mercapto-2-methylpropionamide) were recorded and analysed in solid phase. The EXAFS spectra of the two samples were refined with full multiple scattering path. Geometry optimisations on the Cu I I and Cu I I I complexes were performed by the B3LYP density functional method, with the 6-31G(d,p) basis set, considering different spin multiplicities. The singlet state of the Cu I I I complex was shown to be more stable than the triplet state, and a good agreement between the calculated and the corresponding experimental structure was found. Further single-point calculations on the optimised geometry were carrie…
A Functionalized Noncovalent Macrocyclic Multiporphyrin Assembly from a Dizinc(II) Bis-Porphyrin Receptor and a Free-Base Dipyridylporphyrin
2003
The bis-porphyrin system ZnP 2 , in which two zinc porphyrins are connected by a phenanthroline linker in an oblique fashion, acts as a bifunctional receptor towards the complexation of free-base meso-5,10-bis(4'-pyridyl)-15,20-diphenylporphyrin (4'-cisDPyP). In solution, NMR spectroscopy evidenced quantitative formation of the tris-porphyrin macrocyclic assembly ZnP 2 (4'-cisDPyP), in which the two fragments are held together by two axial 4'-N(pyridyl)-Zn interactions. The remarkable stability of the edifice (an association constant of about 6 x 10 8 M - 1 was determined by UV/Vis absorption and emission titration experiments in toluene) is due to the almost perfect geometrical match betwe…
Ground and excited state polarizabilities and dipole transition properties of benzene from coupled cluster response theory
1999
Abstract The electronic properties and transition properties have been investigated for the lowest singlet electronic states of benzene using coupled cluster response theory. The polarizabilities have been calculated for the ground state and the 1 1 B 2u , 1 1 B 1u 1 1 E 1u and 2 1 E 1u excited states. The dipole allowed transitions out of these states have also been calculated and discussed in the context of the calculated polarizabilities. Oscillator strengths and the second electronic moments of the charge distributions have been used to characterize and identify qualitative features of the individual states. The performance of coupled cluster singles (CCS), the recently proposed CC2 mod…
Excitons and nonlinear optical spectra in conjugated polymers.
1992
Excitons in conjugated polymers are studied theoretically in the Su-Schrieffer-Heeger model supplemented by long-range Coulomb interactions. The relationship between exciton energies and basic interaction parameters is clarified. Linear and third-order nonlinear optical susceptibilities (two-photon absorption, electroabsorption, and third-harmonic generation) have been calculated, elucidating the significance of singlet and triplet excitons and unbound electron-hole pairs. Using only moderate interaction strength, various experiments in polydiacetylene can be interpreted in a consistent way
Theoretical CASPT2 study of the excited state double proton transfer reaction in the 7-azaindole dimer
2006
Accurate CASPT2 calculations on the excited state double proton transfer reaction in the 7-azaindole dimer have been performed on different symmetric and asymmetric pathways along the protons interchange. The presence of a conical intersection connecting the initially photoinduced singlet excited state with a charge transfer state leading both to asymmetric ionic and neutral structures promotes a step-wise mechanism, probably taking place through the ionic intermediate. The concerted path is computed slightly higher in energy in the gas phase.
Corrigendum: An Unusually Small Singlet-Triplet Gap in a Quinoidal 1,6-Methano[10]annulene Resulting from Baird's 4n π-Electron Triplet Stabilization.
2016
Within the continuum of π-extended quinoidal electronic structures exist molecules that by design can support open-shell diradical structures. The prevailing molecular design criteria for such structures involve proaromatic nature that evolves aromaticity in open-shell diradical resonance structures. A new diradical species built upon a quinoidal methano[10]annulene unit is synthesized and spectroscopically evaluated. The requisite intersystem crossing in the open-shell structure is accompanied by structural reorganization from a contorted Mobius aromatic-like shape in S0 to a more planar shape in the Huckel aromatic-like T1. This stability was attributed to Baird’s Rule which dictates the …