Determination of lifetimes and hyperfine splittings of Tl statesnP 3/2 by level-crossing spectroscopy with two-photon excitation

Level-crossing spectroscopy with pulsed two-photon excitation is used to determine life-times and for the first time to determine hyperfine splittings. The experiments have been performed on thalliumnP _3/2 states (n=8, 9 andn=8–11 respectively). By appropriate choice of the polarization and direction of incident light — and, thereby, of the two-photon transition operator — the signal ratio of neighbouring Δm=2 crossings is altered. Thus, in the case of overlapping crossings improved resolution can be obtained without further efforts.     

Experimental lifetimes of the 3p and 3d states of neutral fluorine

The radiative lifetimes of six 3p and 3d neutral fluorine states were measured using the High Frequency Deflection technique. The derived transition probabilities are compared to existing values obtained from shock tube and wall-stabilized arc measurements, theoretical calculations based on Coulomb approximation and semiempirical compilations.     

Heterodyne laser spectroscopy of lithium ions: 23 P fine and hyperfine structure of7Li+

The fine structure (fs) splittings in the 1s2p ³ P _J=1,2,0 multiplet of the helium-like⁷Li⁺ ion were measured with a laser spectrometer. The results with 3σ errors are: Δv ₀₁ (³ P ₀,F=3/2?³ P ₁,F=5/2)=152081.6(2.0) MHz and Δv ₀₂ (³ P ₀,F=3/2?³ P ₂,F=7/2)=82704.3(1.9) MHz. Combining the new precise fs measurements with earlier hyperfine structure (hfs) results from laser-microwave spectroscopy provided improved fs constants:D ₁=?155709.0(2.1) MHz,D ₂=?93049.2(2.0) MHz, and hfs constants:A _c =3679.0(6) MHz,A ₀=51.0(4) MHz, andA _d =?11.3(1) MHz, thus allowing for a stringent test of available theoretical data. The spectroscopic method used in this work opens up the possibility of determining Li⁺, 2³ S?2³ P absolute transition frequencies with a precision of ～2·10^?9.     

The structure and hyperfine splittings of simple phosphoranyl radicals

The ab initio UHF method has been employed to calculate equilibrium geometries and isotopic hyperfine coupling constants for the radicals PH₂, PF₂, PH₄ and PF₄.     

Theoretical and experimental studies of radiative lifetimes of excited electronic states in CO

The electronic dipole transition moment functions of the A ²Π-X ²Σ⁺, B ²Σ⁺-X ²Σ⁺ and B ²Σ⁺-A ²Π transitions and the dipole moment function of the X ²Σ⁺ state of CO⁺ have been calculated using large contracted CI wavefunctions. The computed transition moment functions together with experimental potential energy curves were used to obtain radiative lifetimes of the excited electronic states B ²Σ⁺ and A ²Π. Radiative lifetimes of vibrational levels of the X ²Σ⁺ state were derived from the calculated dipole moment function. The high-frequency deflection technique was used to obtain radiative lifetimes of the ν′ = 0, 1,2 and 3 vibrational levels of the B ²Σ⁺ state and also radiative lifetimes of individual rotational levels of ν′ =0. The calculated radiative lifetimes are shorter than the measured ones by about 10%. The experimental ν′ dependence is reproduced by theoretical calculation. The calculated radiative lifetimes for the A ²Π state are in excellent agreement with lifetimes measured with an ion trap technique.     

Solid-state 23Na and 7Li NMR investigations of sodium- and lithium-reduced mesoporous titanium oxides

Mesoporous titanium oxide synthesized using a dodecylamine template was treated with 0.2, 0.6, and 1.0 equiv of Li- or Na-naphthalene. The composite materials were characterized by nitrogen adsorption, powder X-ray diffraction, X-ray photoelectron spectroscopy, elemental analysis, thermogravimetric analysis, and solid-state 23Na and 7Li NMR spectroscopy. In all cases the wormhole mesoporosity was retained as evidenced by BET surface areas from 400 to 700 m(2)/g, Horvath-Kawazoe pore sizes in the 20 Angstroms range, and a lack of hysteresis in the nitrogen adsorption isotherms. Variable-temperature conductivity studies show that the Li-reduced materials are semiconductors, with conductivity values 3 orders of magnitude higher than those of the Na-reduced materials. Electrochemical measurements demonstrate reversible intercalation/deintercalation of Li+ ions into pristine mesoporous Ti oxides with good cycling capacity. Solid-state 23Na NMR reveals two distinct Na environments: one corresponding to sodium ions in the mesoporous channels and the other corresponding to sodium ions intercalated into the metal framework. 23Na NMR spectra also indicate that the relative population of the framework site increases with increased reduction levels. Solid-state 7Li NMR spectra display a single broad resonance, which increases in breadth with increased reduction levels, though individual resonances inferring the presence of channel and framework Li species are not resolved. Comparisons of the lithium chemical shifts with published values suggests an "anatase-like structure" with no long-range order in the least-reduced samples but a "lithium titanate-like structure" with no long-range order in the higher reduced materials.     

Electronic structure of the radicals NF and NCl. III. The radiative lifetimes of the bΣ and aΔ states

The radiative lifetimes of the b¹Σ⁺ and a¹Δ states have been evaluated by perturbation expansions including X³Σ⁻, a¹Δ, b¹Σ⁺, 1^3,1Π, 2^3,1Π, 2³Σ⁻ and 2¹Σ⁺ states. All wavefunctions result from large MRD CI calculations. The b—X transition is dominated by the parallel transition moment; it is found to be much stronger than the a—X transition. The calculated radiative lifetimes of τ(¹Σ⁺)=18 ms, τ(¹Δ)=2.2 s for NF and τ(¹Σ⁺)=2.5–3.5 ms for NCl are in good accord with corresponding experimentally deduced values. The lifetime for the a¹Δ state in NCl is found to be τ(¹Δ)=1.1 s, ie. much longer than derived from a recent experiment. Its magnitude is consistent with the τ(b¹Σ⁺)/τ(a¹Δ) ratio of similar systems and with the decrease in lifetime from NF to NCl and is thus believed to be quite reliable. A detailed analysis of all contributions of the perturber states to the transition mechanism is made and comparison with the related data in SO, O₂ and S₂ is undertaken. The b-a transition probability dominated by the quadrupole transition is fairly constant in all the systems in the order of A = 0.013 (NF) - 0.0013 (S₂) s⁻¹.     

On the determination of radiative lifetimes of excited Mn I and Mn II levels

Time-resolved laser-induced fluorescence spectroscopy has been used to measure the lifetimes of 46 Mn I and 7 Mn II levels. A high-current hollow cathode produces an effusive beam of manganese atoms and ions in the ground states and in metastable states. Selected states are populated with tunable dye laser pulses. The following fluorescence is measured by means of a Tektronix 1 GHz transient digitizer. Including the separately measured response function of the system in the evaluation procedure the full decay curve can be applied for a determination of the lifetimes. All measurements are performed with linearly polarized laser beams adjusted to the magic angle in order to exclude systematic error sources. A comparison with literature data is given.     

Ab initio transition probabilities,band strengths and lifetimes for the lowest-lying vibrational states of Li+3

By calculating the dipole moments at 65 discrete points on a dipole moment hypersurface and by fitting a power series analytical function to these points, we have determined the ab initio transition probabilities, band strengths and lifetimes for the ten lowest-lying states of ⁷Li⁺₃ (⁶Li⁺₃). Of these, the fourth and tenth states were found to have long lifetimes of the order 4907 s(3344 s) and 1648 s(1093 s) respectively which is in accordance with the fact that transitions from these states to the ground state are dipole forbidden.     

Oscillator strengths and radiative lifetimes for C2: Swan, Ballik-Ramsay, Phillips, and d 3Pig<--c 3Sigmau+ systems

High level ab initio calculations, using multireference configuration interaction (MRCI) techniques, have been carried out to investigate the spectroscopic properties of the singlet A 1Piu<--X 1Sigmag+ Phillips, the triplet d 3Pig<--a 3Sigmau Swan, the b 3Sigmag-<--a 3Piu Ballik-Ramsay, and the d 3Pig<--c 3Sigmau+ transitions of C2. The MRCI expansions are based on full-valence complete active space self-consistent-field reference states and utilize the aug-cc-pV6Z basis set to resolve valence electron correlation. Core and core-valence correlations and scalar relativistic energy corrections were also incorporated in the computed potential energy surfaces. Nonadiabatic and spin-orbit effects were explored and found to be of negligible importance in the calculations. Harmonic frequencies and rotational constants are typically within 0.1% of experiment. The calculated radiative lifetimes compare very well with the available experimental data. Oscillator strengths are reported for all systems: fv'v", where 0相似文献   

Isotropic and antisymmetric double-exchange, zero-field, Zeeman, and hyperfine splittings in trinuclear valence-delocalized [Cu3(7+)] clusters

Valence delocalization in the [Cu3(7+)] trimer is considered in the model of the double-exchange coupling, in which full delocalization corresponds to the migration of the single d(x2-y2) hole and relatively strong isotropic double-exchange coupling. Strong double exchange results in the pairing of the individual spins in the delocalized trimer even at room temperature. The model explains the delocalized singlet 1A1 ground state in the planar Cu3(mu3-O) core by strong double exchange with positive double-exchange parameter t(0), whereas the delocalized triplet ground state of the [Cu3(7+)] trimer, which was observed in the Cu3(mu3-S)2 cluster, may be explained by the double exchange with relatively weak positive t(0): 0 < t(0) < 2J (degenerate 3E ground state) or negative t(0) (triplet 3A2 ground state). An analysis of the splitting of the delocalized degenerate 3E term requires inclusion of the antisymmetric double-exchange interaction, which takes into account the spin-orbit coupling in the double-exchange model. The cluster parameter KZ of the antisymmetric double-exchange coupling is proportional to t(0) and anisotropy of the g factor Deltag(parallel)[Cu(II)], KZ < t(0). Antisymmetric double exchange is relatively large in the [Cu3(7+)] cluster with the d(x2-y2) magnetic orbitals lying in the Cu3 plane [Cu3(mu3-O) core], whereas for the d(x2-y2) magnetic orbitals lying in the plane perpendicular to Cu3, antisymmetric double-exchange coupling is weak [Cu3(mu3-S)2 cluster]. The antisymmetric double-exchange coupling results in the linear zero-field splitting DeltaK = 2[equation: see text]KZ (approximately t(0)) of the delocalized degenerate 3E term that leads to strong anisotropy of the Zeeman splittings in the external magnetic field and a complex electron paramagnetic resonance (EPR) spectrum. The delocalized model of hyperfine interaction explains the hyperfine structure [10 hyperfine lines with the relative intensities 1:3:6:10:12:12:10:6:3:1 and the interval a/3] of the EPR transitions in the triplet states that was observed in the EPR spectra of the Cu3(mu3-S)2 cluster.     

Excited electronic states, transition probabilities, and radiative lifetimes of CAs: a theoretical contribution and challenge to experimentalists

High-level CASSCF/MRCI calculations with a quintuple-ζ quality basis set are reported by characterizing for the first time a manifold of electronic states of the CAs radical yet to be investigated experimentally. Along with the potential energy curves and the associated spectroscopic constants, the dipole moment functions for selected electronic states as well as the transition dipole moment functions for the most relevant electronic transitions are also presented. Estimates of radiative transition probabilities and lifetimes complement this investigation, which also assesses the effect of spin-orbit interaction on the A (2)Π state. Whenever pertinent, comparisons of similarities and differences with the isovalent CN and CP radicals are made.     

Ionic Mobility in Glasses in the ZrF4-BiF3-MF Systems (M = Li,Na, K) as Probed by 7Li, 19F,and 23Na NMR

The ion mobility in new fluoride glasses (mol %) 45ZrF₄ · 25BiF₃ · 30MF (I) (M = Li, Na, K), (70 - x)ZrF₄ · xBiF₃ · 30LiF (II) (15 ≤ x ≤ 35), and 45ZrF₄ · (55-x)BiF₃ · xMF (III) (M = Li, Na; 10 ≤ x ≤ 30) has been studied by ⁷Li, ¹9F, and ²³Na NMR in the temperature range 250–500 K. The character of ion motion in bismuth fluorozirconate glasses I and III is determined by temperature and the nature and concentration of an alkali-metal cation. Major type of ion mobility in glasses I–III at temperature 400–440 K are local motions of fluorine-containing moieties and diffusion of lithium ions (except for the glass with x = 10). The factors responsible for diffusion in the fluoride sublattice of glasses I have been determined. Sodium ions in glasses I and III are not involved in ion transport.     

The Na2 2 3pi(g) state: new observations and hyperfine structure

Many more Na2 2 3pi(g) v = 0-43, omega = 0, 1, 2 levels have been observed by sub-Doppler continuous wave perturbation facilitated optical-optical double resonance fluorescence excitation spectroscopy and the hyperfine structure of the omega = 0 and 2 levels has been resolved. New molecular constants for the less perturbed v = 0-43 levels have been obtained with these new and the previously reported data. The hyperfine coupling scheme of the observed 2 3pi(g) levels is close to Hund's case a(beta) with a Fermi contact constant b(F) = 160+/-5 MHz, which is smaller than the Fermi contact constants of other Na2 triplet Rydberg states, b(F) = 200-245 MHz.     

Thermodynamic properties of Na2Ti6O13 and Na2Ti3O7: electrochemical and calorimetric determination

Standard values of Gibbs free energy, entropy, and enthalpy of Na₂Ti₆O₁₃ and Na₂Ti₃O₇ were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na₂CO₃, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO₂ and O₂. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are Δ_fH_m⁰=(−6277.9±6.5) kJ · mol⁻¹ and S_m⁰=(404.6±5.3) J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Δ_fH_m⁰=(−3459.2±3.8) kJ · mol⁻¹ and S_m⁰=(227.8±3.7) J · mol⁻¹ · K⁻¹ for Na₂Ti₃O₇. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is S_m⁰=399.7 J · mol⁻¹ · K⁻¹ and S_m⁰=229.4 J · mol⁻¹ · K⁻¹ for Na₂Ti₆O₁₃ and Na₂Ti₃O₇, respectively. The phase widths with respect to Na₂O content were studied by using a Na₂O-titration technique.     

Calculated ro-vibrational spectrum of 7Li+3 and 7Li2 6Li+

Calculated ro-vibrational energy levels (J ⩽ 4) and transition intensities are presented for the two most abundant isotopomers of Li⁺₃. The calculations use the recent ab initio potential energy surface of Searles et al. (Spectrochim. Acta 43A, 699 (1987); 44A, 505 (1988); 44A, 985 (1988)). The rotational levels of the ground state and vibrational fundamentals are given in terms of parameterised Hamiltonians due to Watson retaining terms to fourth-order. The small splitting of the degenerate ν₂ mode in the mixed isotopomer leads to strong Coriolis coupling between the ν₂ and ν₃ in ⁷Li₂ ⁶Li⁺.     

Energies,fine structures,and radiative lifetimes for the multiexcited quartet states of B‐like oxygen

Energies for the multiexcited states 1s²2s2pnl and 1s²2p²nl ⁴P^e,o (n ≥ 2) of B‐like oxygen are calculated using Rayleigh–Ritz variation method with configuration interaction. The mass polarization and relativistic corrections are obtained with first‐order perturbation theory. Configuration structures of the high‐lying multiexcited series are identified by energies and contribution to normalization of angular‐spin components. These structures are further checked by calculations of relativistic corrections and fine structure splittings. Hyperfine parameters and hyperfine coupling constants are calculated for the first time. Wavelengths including quantum electrodynamic effect and higher‐order relativistic corrections and lifetimes are also calculated. These results are compared with available results in the literature. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Studies on radiative lifetimes in the 4d 10 ns2 S and 4d 10 nd 2 D sequences of neutral silver

We have performed lifetime measurements in the sequences of² S _1/2 and² D _3/2 states for the alkali-like 4d ¹⁰ ns,nd configurations of neutral silver. Selective stepwise excitations from the 4d ¹⁰ 5s ² S _1/2 ground state were performed using two pulsed dye lasers. Optical transients were recorded and evaluated with regard to the decay time. The lifetime results are compared with those of a theoretical study in which a model potential has been used to describe the polarisation of the 4d shell.     

Theory of laser enhancement and suppression of cold reactions: the fermion-boson 6Li+7Li2<-->(variant Planck's over 2pi omega0) 6Li7Li+7Li radiative collision

We present a nonperturbative time-dependent quantum mechanical theory of the laser catalysis and control of a bifurcating A+BC<-->(variant Planck's over 2pi omega(0))ABC*(v)<-->(variant Planck's over 2pi omega(0) )AB+C reaction, with ABC*(v) denoting an intermediate, electronically excited, complex of ABC in the vth vibrational state. We apply this theory to the low collision energy fermion-boson light-induced exchange reaction, (6)Li((2)S)+(7)Li(2)((3)Sigma(u)(+))<-->(variant Planck's over 2pi omega(0))((6)Li(7)Li(7)Li)*<-->(variant Planck's over 2pi omega(0))(6)Li(7)Li((3)Sigma(+))+(7)Li((2)S). We show that at very low collision energies and energetically narrow (approximately 0.01 cm(-1)) initial reactant wave packets, it is possible to tune the yield of the exchange reaction from 0 to near-unity (yield >or=99%) values. Controllability is somewhat reduced at collisions involving energetically wider (approximately 1 cm(-1)) initial reactant wave packets. At these energetic bandwidths, the radiative reactive control, although still impressive, is limited to the 0%-76% reactive-probabilities range.