Excited Doublet Research Articles

Quantum interference effects in resonance fluorescence and absorption spectra of a V-type three-level atom damped by a broadband squeezed vacuum

The resonance fluorescence spectrum (RFS) and the absorption of a weak probe beam of a V-type three-level atom damped by a broadband squeezed vacuum and driven by a single coherent field which simultaneously couples the two upper states are studied. We consider the interplay between the squeezed field and the vacuum-induced coherence (VIC) between the two possible decay channels. The RFS for a degenerate excited doublet exhibits a high narrowing of the central line. In the situation in which the excited doublet is non-degenerate, we found that the squeezed field breaks the trapping condition attained when induced interference is maximal. A explanation of the main features in terms of dressed atomic states is given. We have also studied the probe absorption spectrum for a resonant driving field. It is shown that the probe may be amplified or absorbed over a wide range of frequencies when both quantum interference and the squeezed vacuum are considered. The sensitivity of the spectrum to the squeezed phase allows the control of the amplification/absorption of the probe signal.

Magnetic Susceptibility and Specific Heat of CePdP and CePdAs.

AbstractFor Abstract see ChemInform Abstract in Full Text.

The excited multiplet states of 5,10,15-tri- n-pentyl-20-(1 ′,1 ′,3 ′,3 ′-tetramethylisoindolin-2 ′-yloxyl-5 ′-yl)porphyrinato zinc(II)

Photo-physical properties of 5,10,15-tri- n-pentyl-20-(1 ′,1 ′,3 ′,3 ′-tetramethylisoindolin-2 ′-yloxyl-5 ′-yl)porphyrinato zinc(II), 1, have been investigated using time-resolved EPR (TREPR) and transient absorption measurements. A formation of the excited doublet (D 1) and quartet (Q 1) states constituted by excited triplet zinc porphyrin (ZnP) and doublet nitroxide is confirmed by TREPR. This is the first D 1 and Q 1 observation in a system where the nitroxide is directly substituted to a porphyrin ligand. Compound 1 exhibits the longest lifetime of any nitroxide–porphyrin systems in the lowest excited state, indicating a relatively weak electron exchange interaction between triplet ZnP and doublet nitroxide.

Anisotropic, thermal, and magnetic properties ofCeAgSb2:Explanation via a crystalline electric field scheme

We have studied the thermal and magnetic properties of a single crystal of ${\mathrm{CeAgSb}}_{2},$ which has a small net magnetic moment of about $0.4{\ensuremath{\mu}}_{\mathrm{B}}$ below the ordering temperature ${T}_{\mathrm{ord}}=9.7\mathrm{K},$ by means of specific heat, thermal expansion, and magnetization measurements. The magnetic part of the specific heat shows a broad peak around 30 K, and the magnetic entropy reaches $R\mathrm{ln}4$ at about 50 K. This indicates that the first excited doublet is situated at about 50 K from the ground state. In addition, the thermal expansion along the tetragonal [001] direction exhibits a clear negative peak around 25 K, which is also attributed to the magnetic excitations between crystalline electric field (CEF) states. These data, together with the anisotropic magnetic susceptibility, were analyzed on the basis of a CEF model, and splitting energies from the ground state to the first and second excited states were estimated to be 48 and 140 K, respectively. Furthermore, the anisotropy in the high-field magnetization was well explained by the present CEF model with the same parameters, where the saturation moment for $H\ensuremath{\Vert}$ [001] is found to be determined by the value of ${g}_{J}{J}_{z}$ of the ground state.

Theoretical study of hyperfine related CIDEP of radical–triplet pairs

Considering the interaction between excited triplet molecule and doublet radical, based on the second-order perturbation theory and the motion equation of density matrix, the spin polarization intensity on the radical was theoretically calculated. The results of calculation indicate that the polarization was hyperfine related. With the overpopulation on doublet spin states of radical–triplet pairs as initial condition, the CIDEP on the radicals were A + A/E pattern and with the overpopulation on quartet spin states of radical–triplet pairs, the CIDEP was E + E/A pattern.

Field Induced Magnetic Ordering in CsFeBr3Studied by High Field ESR

High field ESR technique was applied to the study of the singlet ground state system CsFeBr3, to study the energy structure and the field induced magnetic ordering state, which occurs at low temperature and in a field with the configuration parallel to the c-axis. In low field paramagnetic regime, the complicated spectra were observed and the obtained frequency-field diagram at low temperatures can not be explained within the simple singlet-doublet energy scheme asserted from previous neutron experimental results, indicating that the exchange interaction, which brings a dispersive character on the excited doublet levels, may play an important role to understand the origin of observed ESR modes. One of the modes observed at 2.0 K altered its slope to almost twice one at the field of about 2.9 T, which corresponds to the level crossing field between singlet and the lower branch of doublet states. This behavior is reasonably explained as the direct transition between doublets due to the mixing around level crossing field and is consistent with recently developed theoretical prediction proposed by Lolezhuk and Mikeska. Further, in the high field regime, two broad absorption lines with each line width of about a few tesla were also observed. These two ESR modes depend remarkably on the frequency in such a way that both resonance fields coincide at about 160 GHz and separate linearly with large g-value of 4.8 from each other as the frequency is increased. We present these experimental results in detail and give some possible explanations.

Nonstationary behavior of a high-spin molecule in a bifrequency alternating current magnetic field

An interaction of a high-spin molecule with a bifrequency ac magnetic field, occurring at times much shorter than the molecule relaxation times, has been considered. The molecule is subjected to a dc magnetic field perpendicular to the easy anisotropy axis of the molecule. The bifrequency ac field is a superposition of two ac fields, one of which is perpendicular to the easy anisotropy axis and causes resonant transitions between the lower states of the fundamental and first excited doublets. The other ac field is parallel to the easy anisotropy axis and has a frequency much smaller than the frequency of the first ac field. It has been shown that, first, the molecule can absorb or emit energy, depending on the frequency of the low-frequency ac field, second, the bifrequency ac magnetic field induces tunneling of the molecule magnetization with the Rabi frequency. The conditions of observation of the effects predicted are discussed.

Magnetic susceptibility and specific heat of CePdP and CePdAs

The results of magnetic-susceptibility χ( T) and specific-heat C( T) measurements on single crystals of CePdP and CePdAs and their non-magnetic references LaPdP and LaPdAs between 1.8 and 300 K are reported. It was found that CePdP and CePdAs show ferromagnetic ordering below 5.2 and 6.2 K, respectively. Furthermore, χ( T) and C( T) of CePdAs exhibit a small hump at 4 K which has not been reported so far. This clearly shows that there are successive ferromagnetic transitions in CePdAs. At high temperature, χ( T) of CePdAs is strongly anisotropic, while that of CePdP is rather isotropic. The Schottky-type anomalies around 100 K of CePdP and CePdAs suggest that the first and second excited doublets are separated from the ground state doublet by ∼300 K.

Origin of magnetoresistance anomalies in antiferromagnetic YBa 2Cu 3O 6+ x

Specific d-wave angular dependence of the in-plane magnetoresistance in antiferromagnetic tetragonal YBa 2Cu 3O 6+ x ( x∼0.3) on the orientation of the external magnetic field within the ( a, b) plane is assigned to the effective hole transport through the low-lying excited pure oxygen doublet O2pe u state in CuO 4 plaquette, rather than the ground b 1g(d x 2− y 2 ) state. The external magnetic field is believed to determine the orientation of the strong exchange field for the spin-triplet b 1ge u: 3 E u state of the hole CuO 4 center and owing to the spin–orbit coupling results in a specific orbital polarization of the E u doublet. Namely, this gives rise to the spatial d-wave like anisotropy of the hole transport. The experimental data allow to estimate the parameter of the effective spin Hamiltonian.

LUMINESCENT PROPERTIES OF METAL PORPHYRIN REDUCTION PRODUCTS

We have investigated the luminescent properties of π-anions in Zn and Pd complexes of octaethylporphin and etioporphyrin, and also of protonation products of π-dianions (π-monoanions of phlorins). It is established that the quantum yield of luminescence of π-anion radicals in Zn complexes amounts to 2.9·10−4. The lifetime of the lower excited (doublet) state is estimated to be 120 ± 25 nsec. We failed to reveal the luminescence of π-dianions. In reducing the Pd porphyrins into π-anion radicals and π-dianions, a loss of the luminescent properties is observed. However, the π-monoanion of phlorin in Pd octaethylporphin luminesces. The Zn complex of the phlorin anion also has the same properties. The spectral properties of Zn and Pd phlorin anions are similar: a large Stokes shift is observed at room temperature; on decrease in the temperature to 77 K the fluorescence spectrum becomes narrower, the maximum of the spectrum shifts strongly to the blue region, and the quantum yield of luminescence increases. The special features of the spectral properties of phlorin anions are explained by conformation changes in the excited state. It is found that in a solution at room temperature Pd phlorin anions quench the phosphorescence of neutral Pd porphyrins.

Specific heat of CePdP and CePdAs

The specific heat C(T) was measured between 1.8 and 300K for single crystals of CePdP and CePdAs and their non-magnetic references LaPdP and LaPdAs. It was found that CePdP and CePdAs show a ferromagnetic ordering below 5.2 and 6.2K, respectively. We found a small hump in C(T) of CePdAs at 4K which have not been reported so far, suggesting successive ferromagnetic transitions in CePdAs. The Schottky-type anomalies around 100K were revealed in the magnetic contribution to C(T) for CePdP and CePdAs. It is suggested that the first and second excited doublets are separated above the ground state by ∼300K.

The Jahn–Teller-effect formation of the non-magnetic state of the Co3+ ion in LaCoO3

It is shown that the Co3+ ion can have a non-magnetic ground state as the realization of the Jahn–Teller effect. This non-magnetic localized singlet ground state with a highly magnetic excited doublet is formed by the trigonal distortion of the local octahedral surrounding. Such structure is exactly accounted for by crystal-field interactions if the intra-atomic spin–orbit coupling is correctly taken into account. The presented crystal-field-based approach can be applied to other Co3+ and Fe2+ ion compounds.

Conditions for forming excited multiplet states: magnetic interactions between excited triplet (phthalocyaninato)zinc and doublet nitroxide radical

Excited state phthalocyanine complexes comprising (tetra-tert-butylphthalocyaninato)zinc (ZnPc) coordinated by nitroxide radicals have been studied by time-resolved electron paramagnetic resonance (TREPR). Five ZnPc complexes coordinated by an axial ligand containing a nitroxide radical NRX (where X (= 4, 5, 6, 8 or 10) denotes the number of bonds from the zinc to the nitroxide nitrogen) were selected, and the magnetic interactions between the excited triplet ZnPc and respective NRX have been investigated in terms of the conditions for forming the excited quartet (Q1) state. Optimum structures calculated using a PM3 Hamiltonian show that the bond number X is well correlated with the distance between zinc and nitroxide nitrogen atoms (Δr). TREPR spectra of ZnPc complexes, which are coordinated by NR8 or NR10, are almost the same as that of ZnPc coordinated by pyridine (ZnPc–py), indicating that the electron exchange interaction, J, between the excited triplet ZnPc and doublet nitroxide is much smaller than the zero field splitting parameter D value (D(T1) = 0.720 GHz) of the excited triplet ZnPc–py. On the other hand, TREPR spectra of the NR4, NR5 and NR6 complexes are assigned to the Q1 state constituted by the excited triplet ZnPc and doublet nitroxide radical. The D value of the Q1 state (D(Q1)) decreases in the order ZnPc–NR6 (0.205 GHz) > ZnPc–NR5 (0.190 GHz) > ZnPc–NR4 (0.165 GHz). This decrease is interpreted in terms of a magnetic dipole–dipole interaction between the triplet ZnPc and doublet nitroxide, which is opposite in sign to D(Q1), and increases in the order ZnPc–NR6 < ZnPc–NR5 < ZnPc–NR4. Calculations of resonance magnetic fields indicate that the |J| values of the NR4, NR5 and NR6 complexes are larger at least than the D(T1) value. It is found that the D and |J| values are well correlated with the bond number X and distance Δr. This EPR study is useful for understanding the photophysical and photochemical properties of chromophores.

Relationship between Electron Spin Polarization, Electron Exchange Interaction, and Lifetime: The Excited Multiplet States of Phthalocyaninatosilicon Covalently Linked to One Nitroxide Radical

We have studied phthalocyaninatosilicon (SiPc) covalently linked to one nitroxide radical by the combined use of transient absorption and time-resolved electron paramagnetic resonance (TREPR) spectroscopies and succeeded in clarifying the relationship between the electron spin polarization (ESP), excited-state lifetime, and electron exchange interaction between the excited triplet SiPc and doublet nitroxide. It is found that the lifetime of the excited triplet SiPc is dependent on the linking nitroxide radical and correlates well with the magnitude of the electron exchange interaction. The ESPs due to both D1−Q1 mixing (the D1 and Q1 states consist of the excited triplet SiPc and doublet nitroxide radical) and spin−orbit coupling (SOC) are observed by systematically changing the electron exchange interaction. It is found that the ESP of the radical−triplet pair changes from SOC type to D1−Q1 mixing type with increasing degree of electron exchange interaction. These relationships are important for understanding the excited-state dynamics of the radical−triplet pair system.

Structural Phase Transition in K1-xCsxDy(WO4)2 Single Crystals

Single crystals of dysprosium potassium (caesium) double tungstates were grown both by typical flux growth and Top Seeded Solution Growth. K 2 W 2 O 7 was used as flux. Potassium tungstate provides broad range of growth temperatures, rather low volatility, and does not introduce additional components into the melt. K 1-x Cs x Dy(WO 4 ) 2 crystals belong to the monoclinic syngony (α-KY(WO 4 ) 2 structure) and has the space group C2/c. Dy ions are situated on the two-fold axes (C 2 ) (which coincide with the crystallographic [010] directions) inside distorted octahedra of oxygen ions. KDy(WO 4 ) 2 is known to undergo a structural phase transition of Jahn-Teller type at 6.38K. The influence of caesium ions on structural phase transition was investigated. Spectroscopic studies of this compound at low temperature have revealed some peculiarities of optical absorption spectra. The ground state of the Dy 3+ ions is split into Kramer's doublets with the first excited doublet lying closely to the ground doublet what determines the thermal behaviour of absorption spectra. The increase of the distance between the Dy 3+ lowest doublets observed at low temperature is interpreted as the result of the cooperative Jahn-Teller effect.

Magnetic, thermal, and transport properties of single crystals of antiferromagnetic Kondo-latticeCe2PdSi3

Magnetization, heat capacity, electrical resistivity, thermoelectric power, and Hall effect have been investigated on single-crystalline ${\mathrm{Ce}}_{2}{\mathrm{PdSi}}_{3}.$ This compound is shown to order antiferromagnetically below N\'eel temperature ${(T}_{N})\ensuremath{\sim}3\mathrm{K}.$ The Sommerfeld coefficient far below ${T}_{N}$ is found to be about $110{\mathrm{m}\mathrm{J}/\mathrm{K}}^{2}\mathrm{mol}\mathrm{Ce},$ which indicates the heavy-fermion character of this compound. The transport and magnetic properties exhibit large anisotropy with an interplay between crystalline-electric-field (CEF) and Kondo effects. The sign of thermoelectric power is opposite for different directions at high temperatures and the ordinary Hall coefficient is anisotropic with opposite sign for different geometries, indicating the anisotropic Fermi surface. The CEF analysis from the temperature dependence of magnetic susceptibility suggests that the ground state is $|\ifmmode\pm\else\textpm\fi{}\frac{1}{2}〉.$ The first and the second excited CEF doublet levels are found to be located at about 30 and 130 K, respectively. The Kondo temperature is estimated to be the same order as ${T}_{N},$ indicating the presence of a delicate competition between the Kondo effect and magnetic order.

Excited Doublet States of Electrochemically Generated Aromatic Imide and Diimide Radical Anions

The radical anions of aromatic diimides have been implicated recently in a wide variety of photochemical electron transfer reactions. Photoexcitation of these radical anions produces powerfully reducing species. Yet, the properties of the π* excited doublet states of these organic radical anions remain obscure. The radical anions of three aromatic imides with increasingly larger π systems, N-(2,5-di-tert-butylphenyl)phthalimide, 1, N-(2,5-di-tert-butylphenyl)-1,8-naphthalimide, 2, and N-(2,5-di-tert-butylphenyl)perylene-3,4-dicarboximide, 3, as well as the three corresponding aromatic diimides, N,N‘-bis(2,5-di-tert-butylphenyl)pyromellitimide, 4a, N,N‘-bis(2,5-di-tert-butylphenyl)-naphthalene-1,8:4,5-tetracarboxydiimide, 5a, and N,N‘-bis(2,5-di-tert-butylphenyl)perylene-3,4:9,10-tetracarboxydiimide, 6, were produced by electrochemical reduction of the neutral molecules in an optically transparent thin layer electrochemical cell. The radical anions of these imides and diimides all exhibit intense visible and weaker near-IR absorption bands corresponding to their D0 → Dn transitions. Excited states of the radical anions were generated by subpicosecond excitation into these absorption bands. Excitation of 1•- and 2•- resulted in decomposition of these radical anions, whereas excitation of 3•-−6•- yielded transient spectra of their D1 → Dn transitions and the lifetimes of D1. The lifetimes of the D1 excited states of the radical anions of 3•-−6•- are all less than 600 ps and increase as the D0−D1 energy gap increases. These results impose design constraints on the use of these excited radical anions as electron donors in electron-transfer systems targeted toward molecular electronics and solar energy conversion.

Measurement of the 1s2s2p 4P°5/2–1s2p3d 4F°9/2 Electric-Quadrupole Transition in Doubly Excited N4+, O5+, F6+ and Ne7+ Lithium-like Ions

Doubly excited ions have been obtained in one-electron capture processes by metastable ions from Cs (6s). Incident heliumlike ions have been prepared in high metastable fractions by collision in a gas cell of hydrogenlike ions produced by an ECR ion source. The main interest of this work was to find the electric-quadrupole transition 1s2s2p 4P°5/2–1s2p3d 4F°9/2 among the doubly excited quartet and doublet systems of 3-electron ions. Although E2 transitions are in principle highly forbidden, the 2s 4P°5/2–3d 4F°9/2 transition has been measured in N4+, O5+, F6+ and Ne7+ by vuv spectroscopy taking advantage of non-negligible branching ratios and highly-state-selective-collisions.

Dimer splitting of Er 3+ in Cs 3Er 2X 9 (X=Cl,Br): mystery solved

Inelastic neutron scattering (INS) measurements were performed on the rare earth dimer compounds Cs 3Er 2X 9 (X=Cl,Br). The crystalline electric field (CEF) parameters were determined. The lack of any exchange splitting associated with the CEF transitions can be explained by the large single-ion anisotropy for Er. Specific heat and susceptibility data support the picture of an almost pure Ising system, which splits the lowest CEF state in the presence of the dimer interaction into a non-magnetic ground-state doublet and a magnetic excited doublet without any allowed transition between these two dimer states.

Theoretical Study of the Electronic States of AlS, AlS+ and AlS-

The spectroscopic constants of the excited doublet and quartet states of AlS have been calculated from potential energy functions obtained by the internally contracted multireference configuration interaction (MRCI) approach. Most of these states have not yet been observed. The shape of the electric dipole and transition moment functions are discussed. The spin−orbit constants and the spin−orbit couplings between different states have been evaluated for those cases in which such couplings are responsible for the perturbations of the spectra. The results are compared with similar data for the isoelectronic AlO. For the low lying electronic states of the AlS cation, the potential energy functions and the spectroscopic constants are reported. The electronic ground state of AlS- was found to be the only bound state.