Excited Doublet Research Articles

Theoretical study of the electronic states of AlO and AlO −

The spectroscopic constants of the excited doublet and quartet states of aluminium oxide have been calculated from potential energy functions obtained by the ab initio MRCI approach. Such constants are given also for several states that have not yet been observed. The characteristics of the calculated electric dipole and transition moment functions are discussed in connection with the ionicity and avoided crossing regions of the excited states. The spin–orbit interactions between electronic states have been calculated for those cases where this type of coupling was assumed to be responsible for pertubations of the spectra. Also for the bound electronic ground state of the AlO − anion the spectroscopic constants are given and its photoelectron spectrum is discussed.

Coupled cluster calculations for three low-lying doublet states of linear C 10−

Making use of a large basis set of 270 contracted Gaussian-type orbitals partially restricted coupled-cluster calculations including connected triple substitutions (RCCSD(T)) have been carried out for the ground state X̃ 2Π u and two low-lying excited doublet states ( 2Σ g + and 2Π g) of linear C 10 −. The calculated T e value for the 2Π g state amounts to 10 890 cm −1, in close agreement with the T o value of 10 338 cm −1 obtained by absorption spectroscopy in a neon matrix. The observed peaks at 12 330 and 12 430 cm −1 are assigned to the 2 0 1 and 1 0 1 transitions. For the 2Σ g + state, we predict a T e value of 9 951 cm −1. Besides the adiabatic peak, the 2 0 1 transition shows up strongest in the 2Σ g +←X̃ 2Π u band.

Spectroscopy of NbO: Characterization of the Doublet Manifold

Doublet bands of NbO in the near infrared region have been observed in emission with FTS techniques using an electrodeless 2450 MHz discharge as a source. Transitions involving the vibrational levelsv= 0–4 of a low-lyinga2Δ state of configuration σ2δ and four additional doublet states (c2Π,d2Δi,e2Φ, andf2Πi) have been recorded at high resolution. Furthermore, a2Σ state, assigned asb2Σ−, has been observed through thec2Π (v= 0) →b2Σ−(v= 0, 1) transitions in the 1.6 μm region. Rotational analyses of the doublet bands have been performed. Most of the excited doublet states lie only slightly above or below the well-knownB4Π state. The density of states is fairly high immediately aboveB4Π, and characterizations of some of the states in this region involve difficulties. A currently unanalyzed band, centered at 11 820 cm−1, has been preliminarily attributed to theA4Π → X4Σ−(0, 0) transition. Nuclear hyperfine effects are barely detectable in orbitally degenerate states of the doublet manifold at Doppler-limited resolution, while theb2Σ−state of configuration σδ2shows partly resolved magnetic hyperfine structure (b= −0.08191 cm−1). Large-scale all-electron CI calculations have been performed on doublet and quartet manifolds of NbO up to 22 000 cm−1. The calculations have been performed in two steps. In the first step, the spin–orbit effects within electronic states were not considered. An excellent overall agreement with experimental energies was obtained, except for thed2Δistate. In the second step, all spin–orbit interactions were included. Also these calculations resulted in a good agreement with the experimental observations. The calculations also predict three hitherto unobserved low-lying states:4Φ at 8545 cm−1,2Γ at 8430 cm−1and2Σ+at 9648 cm−1.

Quantum interference in resonance fluorescence for a driven V atom

We investigate the effect of quantum interference between the two transition pathways from the excited doublet to the ground level of a driven V atom on the spectral features of the resonance fluorescence emission. The ultranarrow spectral line at line center, which arises due to quantum interference, occurs over a wide range of parameters. The smaller the ratio of the excited doublet splitting to the effective Rabi frequency, the more pronounced the spectral line narrowing. However, the fluorescence emission is completely quenched when the atomic dipole moments are exactly parallel and the driving field is tuned to the average frequency of the atomic transitions. The narrow line is due to the slow decay rate of one dressed state, while the quenching arises from dressed-state trapping. A finite laser linewidth destroys the spectral narrowing features and the fluorescence quenching.

Paramagnetic NMR shifts in cyanoferricytochrome c: Investigation of thermal stability and deviations from Curie law behaviour

The paramagnetic shifts of 13C nuclei positioned α to the haem in cyanoferricytochrome c are reported and analysed in terms of molecular orbitals based on D 4h symmetry with a rhombic perturbation. The temperature dependence of the Fermi contact and dipolar shifts of the haem and axial histidine ligand show deviations from Curie Law behaviour which are explained by a Boltzmann distribution between partially filled 3e( π) molecular orbitals and the ground and first excited state Kramers doublets. The comprehensive explanation of the temperature dependence of the paramagnetic shifts leads to the conclusion that there is no detectable temperature dependence of the haem orientation or that of the His ligand orientation. This work also provides evidence for the role of the axial His ligand in determining the orientation of the magnetic z-axis.

A Two-Dimensional EPR Nutation Study on Excited Multiplet States of Fullerene Linked to a Nitroxide Radical

Photoexcited states of 3,4-fulleropyrrolidine-2-spiro-4‘-[2‘,2‘,6‘,6‘-tetramethyl]piperidine-1‘-oxyl (1) were studied by the two-dimensional (2D) EPR nutation method in toluene glass. 2D nutation spectra were observed by varying a pulse length of the first microwave pulse in the spin echo experiment. Three kinds of nutation frequencies were obtained from analyses of the 2D spectra and assigned to those of the excited quartet and doublet states on the basis of the fictitious spin-1/2 theory. The obtained EPR parameters such as g-values, hyperfine coupling constants, and zero-field splittings were discussed in terms of the spin Hamiltonian for doublet and quartet states.

Ab initio molecular orbital study of excited electronic states of the vinyl radical

Eight excited doublet electronic states of C 2H 3 have been studied using multireference configuration interaction calculations. Close agreement of the excitation energies with experiment is found for the à 2A″, 5 2A′ (σ-n), and 3 2A″ (π-R) states where the experimental data are available. The undiscovered B 2 2A″ (n - π ∗) state is predicted to have the adiabatic and vertical excitation energies of 33530 and 38546 cm −1, respectively. The π-π ∗ C 2 2A′ state with the vertical energy of 45001 cm −1 is predicted to be difficult to observe because of the small oscillator strength.

An x-ray diffraction and magnetic susceptibility study of

Polycrystalline samples of the new semimagnetic semiconductor (x = 0.06, 0.12, 0.25, 0.39, 1.00, 1.40, 1.80) were obtained by ceramic technology. An x-ray diffraction experiment was performed on all of the samples at room temperature. These data provided the basis for Rietveld refinements. The refinements showed that ions preferentially occupy the 24d position. The lattice constants and the mean cation - anion distances decrease linearly with the -ion concentration. The inverse magnetic susceptibilities for all of the samples depend linearly on the temperature for . In this region only the lowest Kramer's doublet is populated, and for that level the effective magnetic quantum number is deduced. The Curie - Weiss paramagnetic temperatures obtained from the low-temperature region depend linearly on the concentration x. Over the whole experimental region , the magnetic susceptibility deviates from the Curie - Weiss law, and its calculation requires inclusion of the first excited Kramer's doublet. The effective magnetic quantum number and energy gap of the first excited doublet were deduced.

O(1/mQ)corrections to masses of excited heavy mesons from QCD sum rules

The ${O(1/m}_{Q})$ corrections to masses of excited heavy mesons are studied with sum rules in the heavy quark effective theory. Numerical results for the matrix elements of the heavy quark kinetic energy operator $\mathcal{K}$ and chromomagnetic interaction operator $\mathcal{S}$ are obtained for the lowest excited doublets ${(0}^{+}{,1}^{+})$ and ${(1}^{+}{,2}^{+})$.

Electron-Spin Polarizations Generated from Interactions between Excited Triplet Porphyrins and Stable Radicals Studied by Time-Resolved Electron Paramagnetic Resonance

Time-resolved EPR studies were made on CIDEP mechanisms in the system of excited triplets (T) and doublets (D) using various kinds of porphyrins and nitroxide radicals. The CIDEPs were investigated by observing both signals of T and D and discussed in terms of an electron-spin polarization transfer (ESPT) and a radical−triplet pair mechanism (RTPM). It is demonstrated for the first time that ESPT is actually existent by comparing the triplet and doublet CIDEP signals. The ESPT process was found to be diffusion-controlled in toluene and 2-butanol, and an effective distance for ESPT was estimated as <11 A. For RTPM, an enhancement of CIDEP polarization was observed by axial ligation of radicals to zinc porphyrins. We also found novel CIDEP involving molecular oxygen, which is interpreted by RTPM between singlet molecular oxygen and stable radicals.

Incommensurate magnetic structure and crystal field in ErNi2B2C Studied by 166Er Mössbauer spectroscopy and specific heat measurements

166Er Mossbauer absorption spectra have been recorded in the superconductor ErNi2B2C (Tc = 10 K), in zero field and in the temperature range 1.4 K–40 K. The spectra in the magnetically ordered phase (TN ≃ 5.5 K) are characteristic of an incommensurate magnetic structure with a maximum Er3+ moment of 8.2 μB. We show that the magnetic transition is first order, with a small temperature range where magnetically ordered and paramagnetic domains coexist. The analysis of the magnetic and quadrupolar hyperfine interactions below and above TN suggests that the Er3+ ground doublet is close to |J = 15/2; Jz = ± 1/2 > and shows that there is a low lying (≃ 10 K) excited doublet. The measured Er3+ electronic relaxation rate 1/T1 shows an anomaly at 10 K (Tc suggesting that the conduction electrons that are exchange coupled to the 4f spin take part in the formation of the superconducting state. We also present specific heat data for ErxY1 − xNi2B2C and Er0.2Lu0.8Ni2B2C which also evidence a low lying doublet and from which we propose a modified (improved) Er3+ crystal field level scheme (0, 9, 62, 71, 73, 181, 212 and 216 K) where the energies of the higher levels are consistent with published neutron scattering data.

Ultranarrow Spectral Lines via Quantum Interference.

We show that ultrasharp spectral lines, with widths 2 orders of magnitude below the natural width, may be produced in the resonance fluorescence of a V-type three-level atom excited by a single-mode laser field when the dipole moments are nearly parallel. The smaller the splitting of the excited doublet, the narrower the line. This effect is due to quantum interference between the two transition pathways.

High-Frequency Electron Paramagnetic Resonance of Tm3+ Ions in Lanthanum and Thulium Ethylsulphate Single Crystals.

We have observed electron paramagnetic resonance and far-infrared absorption of the transitions between the singlet ground state and the first excited doublet of the Van Vleck paramagnetic ${\mathrm{Tm}}^{3+}$ ion in ethylsulphate crystals in fields up to 10.5 T. The interaction of the Stark levels with a phonon state is clearly shown. The EPR of ${\mathrm{Tm}}^{3+}$ in the 1000--1600 GHz range are single Lorentzians in lanthanum ethylsulphate but are asymmetric and richly structured in thulium ethylsulphate. This work illustrates the usefulness of high-frequency EPR in the study of Van Vleck paramagnets, which are inaccessible by EPR at conventional frequencies.

EPR and Magnetic Susceptibility Studies of Cobalt(II)- and Nickel(II)-Substituted Azurins from Pseudomonas aeruginosa. Electronic Structure of the Active Sites

The electronic properties of cobalt(II)- and nickel(II)-substituted azurins from Pseudomonas aeruginosa have been investigated. EPR data for the cobalt derivative and paramagnetic susceptibility data for the nickel derivative are reported. The EPR spectrum of Co(II)−azurin shows the typical pattern of a Kramers' doublet (±1/2) associated with an S = 3/2 ground state in a distorted axial symmetry environment. The temperature dependence of the EPR intensities shows that this Kramers' doublet is the excited doublet and, therefore, that the corresponding zero-field splitting parameter D is negative (∼−3.5 cm-1). The mean g value is equal to 2.3. Nickel(II) azurin exhibits an effective magnetic moment μeff = 2.8 μB (Bohr magnetons), constant in the temperature range 120−30 K. The magnetic moment decreases and reaches the value of 1.80 μB at 5 K. From the temperature dependence of the susceptibility, the fitting of the data to the theoretical S = 1 susceptibility equation leads to a zero-field splitting paramet...

Stilbene Radical Anions in the Excited Doublet State

Stilbene radical anions (St•-) in the second excited doublet state generated by a pulse radiolysis−laser flash photolysis combined method undergo unimolecular isomerization from c-St•- to t-St•-, photoelectron ejection, and electron transfer to biphenyl added as a quencher. From the selective electron transfer from the St•- D2 states to biphenyl (Bp), kBpτ = 10.7 and 17.8 M-1 were obtained where kBp and τ denote the rate constants of the electron transfer and the lifetimes of the c-St•- and t-St•- D2 states, respectively. The τ values are estimated to be approximately 1.5 ± 0.4 ns and 2.5 ± 0.7 ns for the c-St•- and t-St•- D2 states, respectively, from kBpτ assuming the diffusion-controlled rate constant for kBp. The shorter τ of the c-St•- D2 state is attributed to isomerization via twisting about the central CC double bond. The τ values of the c-St•- and t-St•- D2 states are 1 order of magnitude longer than those of c-St•+ and t-St•+ D2 states. The transient phenomena of the D2 states of c-St•- and t-St...

Absorption Spectra of Co(II)Ions Doped in Magnesium Thallium Sulphate Hexahydrate

Abstract The optical obsorption spectrum of Co(II) ions doped in magnesium thallium sulphate hexahy­ drate is studied at room and liquid nitrogen temperatures. The crystal exhibits characteristic absorption of the Co(II) ion in the visible and near infrared. The observed bands are assigned to transitions from the ground state 4T1g (F) to various excited quartet and doublet levels of the Co(II) ion in octahedral symmetry. The splitting of one of the bands at liquid nitrogen temperature is explained to be due to spin-orbit splitting. All band positions have been fitted by the parameters B, C, Dq and ξ.

Magnetic, Thermal and Transport Properties of CeNiGa2

We have measured the electrical resistivity ρ , thermoelectric power S , Hall coefficient R H , magnetic susceptibility χ , magnetization M and specific heat C of CeNiGa 2 and LaNiGa 2 polycrystalline samples. For CeNiGa 2 , an antiferromagnetic (AF) transition was found at T N =4 K. The γ value of 490 mJ/K 2 mol at T ≪ T N indicates the enhanced electron mass even in the AF state. At the same temperature region, ρ shows a T 2 dependence, the coefficient of which follows the Kadowaki-Woods plot. From C ( T ), it is found that the first excited doublet is lying at ∼30 K and the Kondo temperature has the same order. The observed broad peaks in ρ at 20 K and S at 12 K are explained by the combination of the crystal field and the Kondo effect. LaNiGa 2 shows a bulk superconductivity with the transition temperature of 2.0 K.

Electronic spectrum of S2-, the electron affinity of S2, and the binding energies of neutral and anionic S3 clusters.

The low-lying electronic states of the ${\mathrm{S}}_{2}^{\mathrm{\ensuremath{-}}}$ anion have been investigated by quantum-chemical methods incorporating an extensive treatment of electron correlation. All excited doublet states that can be reached in spin- and dipole-allowed transitions from the $^{2}\mathrm{\ensuremath{\Pi}}_{\mathit{g}}$ ground state of the anionic disulfur molecule as well as the lowest quartet state $^{4}\mathrm{\ensuremath{\Sigma}}_{\mathit{u}}^{\mathrm{\ensuremath{-}}}$ are characterized by their spectroscopic constants, excitation energies, and transition dipole matrix elements with the ground state. Furthermore, an accurate calibration of the employed theoretical methods with respect to the electron affinity of the sulfur atom, the potential energy curves for the ground states of ${\mathrm{S}}_{2}$ and ${\mathrm{S}}_{2}^{\mathrm{\ensuremath{-}}}$, the electron affinity of ${\mathrm{S}}_{2}$, and the binding energies of the neutral and anionic ${\mathrm{S}}_{3}$ clusters is presented.

Lifetimes and Transient Phenomena of Stilbene Radical Cations in the Second Excited Doublet State

Lifetimes and Transient Phenomena of Stilbene Radical Cations in the Second Excited Doublet State

Optical Absorption Spectrum of Co2+ Ion Impurities in Lithium Sodium Potassium Sulphate Single Crystal

AbstractOptical absorption spectrum of Co2+ ions doped in lithium sodium potassium sulphate single crystal has been studied at room and liquid nitrogen temperatures. The observed bands are assigned as transitions from the ground 4T1g(F) to various excited quartet and doublet levels of Co2+ ion in octahedral symmetry. The splitting in one of the bands at liquid nitrogen temperature has been explained as due to spin‐orbit interaction. All the observed band positions have been fitted with the parameters B, C, Dq and ζ.