Suppression of angular momentum transfer in cold collisions of transition metal atoms in ground States with nonzero orbital angular momentum

The Zeeman relaxation rate in cold collisions of Ti(3d(2)4s(2) 3F2) with He is measured. We find that collisional transfer of angular momentum is dramatically suppressed due to the presence of the filled 4s(2) shell. The degree of electronic interaction anisotropy, which is responsible for Zeeman relaxation, is estimated to be about 200 times smaller in the Ti-He complex than in He complexes with typical non-S-state atoms.     

Magnetic trapping and Zeeman relaxation of NH (X3Sigma-)

NH radicals are magnetically trapped and their Zeeman relaxation and energy transport collision cross sections with helium are measured. Continuous buffer-gas loading of the trap is direct from a room-temperature molecular beam. The Zeeman relaxation (inelastic) cross section of magnetically trapped electronic, vibrational, and rotational ground state NH molecules in collisions with 3He is measured to be 3.8+/-1.1 x 10(-19) cm(2) at 710 mK. The NH-He energy transport cross section is also measured, indicating a ratio of diffusive to inelastic cross sections of gamma=7 x 10(4), in agreement with recent theory [R. V. Krems, H. R. Sadeghpour, A. Dalgarno, D. Zgid, J. K?os, and G. Cha?asiński, Phys. Rev. A 68, 051401 (2003)10.1103/PhysRevA.68.051401].     

Spin diffusion of correlated two-spin states in a dielectric crystal

Reciprocal space measurements of spin diffusion in a single crystal of calcium fluoride (CaF2) have been extended to dipolar ordered states. The experimental results for the component of the spin diffusion rate parallel to the external field are D(parallel)(D)=29+/-3x10(-12) cm(2)/s for the [001] direction and D(parallel)(D)=33+/-4x10(-12) cm(2)/s for the [111] direction. The measured diffusion rates for dipolar order are faster than those for Zeeman order and are considerably faster than predicted by simple theoretical models. It is suggested that constructive interference in the transport of the two-spin states is responsible for this enhancement. As expected, the anisotropy in the diffusion rates is observed to be significantly less for dipolar order compared to the Zeeman case.     

Direct observation of nuclear spin diffusion in real space

Images directly visualizing the spatial spin-diffusion process are reported. The measurements were performed using a magnetic resonance force microscope. The field gradient associated with the force-detection experiment is large enough to affect the spin dynamics and a modified kinetics of the spin-diffusion process is observed. The effects of the gradient were compensated for by a pulse scheme and a pure Zeeman diffusion rate constant of D=(6.2+/-0.7)x10{-12} cm{2}/s in CaF2 was observed.     

What determines the K- multiplicity at energies around (1-2)A GeV?

In heavy ion reactions at energies around (1-2)A GeV the measured K- yields appear rather high as compared to pp collisions as shown by the KaoS Collaboration. Employing quantum molecular dy-namics simulations, we show that this is caused by the fact that the dominant production channel is not BB-->BBK+K- but the mesonic Lambda(Sigma)pi-->K-B reaction. Because the Lambda (Sigma) stem from the reaction BB-->Lambda(Sigma)K+B, the K+ and the K- yield are strongly correlated, i.e., the K(-)/K(+) ratio occurs to be nearly independent of the impact parameter as found experimentally. The final K- yield is strongly influenced by the K+N [due to their production via the Lambda(Sigma)] but very little by the K-N potential.     

Direct observation of resonant four-photon parametric mixing conditioned by the difference of atomic multipole relaxation rates

Experimental evidence of previously predicted relaxation induced parametric processes is presented. Parametric interaction of orthogonal linearly polarized waves has been observed in the 2s₂-2p₁ (j = 1 → j = 0) Ne transition under λ = 1.52 μm He-Ne laser pumping. Coherence transfer between Zeeman sublevels eliminates the ban of the parametric interaction of orthogonal linearly polarized waves. This transfer is connected with collisions and photon-trapping processes resulting in the difference between relaxation rates of the electric quadrupole and magnetic dipole moments of the Ne atoms in the 2s₂ level.     

Atom-molecule collisions in an optically trapped gas

Cold inelastic collisions between confined cesium (Cs) atoms and Cs2 molecules are investigated inside a CO2 laser dipole trap. Inelastic atom-molecule collisions can be observed and measured with a rate coefficient of approximately 2.6 x 10(-11) cm3 s(-1), mainly independent of the molecular rovibrational state populated. Lifetimes of purely atomic and molecular samples are essentially limited by rest gas collisions. The pure molecular trap lifetime ranges 0.3-1 s, 4 times smaller than the atomic one, as is also observed in a pure magnetic trap. We give an estimation of the inelastic molecule-molecule collision rate to be approximately 10(-11) cm3 s(-1).     

Laser-Excited Fluorescence Spectra of Strontium Monoiodide

Fluorescence spectra of strontium monoiodide excited by Ar++ and Kr+ laser lines have been analyzed by Fourier transform spectrometry. Rotational levels have been populated either directly or after collisional relaxation: (i) in D2Sigma+ (v = 0, 1) by ultraviolet lines of Ar++, inducing numerous fluorescence transitions ending in the levels v = 0-3 of the strongly interacting A2Pi and B2Sigma+ states, (ii) in A2Pi3/2 (v = 0-4) by Kr+ line at 676.44 nm, de-exciting into transitions to X2Sigma+ (v = 0-6). Deperturbed constants for A2Pi and B2Sigma+ states and A approximately B interaction parameter are calculated from the numerical treatment of D2Sigma+ (v = 0, 1) --> A2Pi (v = 0-3) approximately B2Sigma+ (v = 0-3) transitions. Rotational constants for D2Sigma+ (v = 0, 1) are obtained for the first time. The wavenumbers of some 670 fluorescence lines are cataloged. Copyright 1999 Academic Press.     

Electron spin polarization in an excited triplet-radical pair system: Generation and decay of the state

A computational model to simulate electron spin polarization in the three-spin-1/2 system composed of the molecular excited triplet state of (tetraphenylporphinato)zinc(II) (ZnTPP) and the doublet ground state of the 3-(N-nitronyl-notroxide) pyridine (3-NOPy) stable radical is proposed. The model is based on numerical solutions of the stochastic Liouville equation for the diffusively rotating system where the magnetic dipolar, isotropic Heisenberg exchange, and anisotropic Zeeman electron spin interactions are taken into account in a full measure, whereas the intersystem crossing processes between the singlet and triplet states of ZnTPP are considered in terms of kinetic equations for the relevant spin density matrices. Additional longitudinal and transversal paramagnetic relaxation caused by relative rotation motions of the ZnTPP and 3-NOPy moieties is taken into consideration in the form of the generalized relaxation operator.     

N_2(B~3Ⅱ_g)高振动态在Xe原子中的碰撞激发和弛豫

在用双光子激发产生的Xe(5p~56p)原子与N_2分子碰撞过程中,有效地生成了N_2(B~3П_g,v=9～14)振动激发态.观察到相应的Δv=4的N_2(B~3П_g-A~3∑_u~+)辐射跃迁萤光,测量了Xe(6p)原子在N_2中的淬灭速率常数,对碰撞弛豫过程进行了讨论.     

Observation of the Heavy Baryons Sigma b and Sigma b*

We report an observation of new bottom baryons produced in pp collisions at the Tevatron. Using 1.1 fb(-1) of data collected by the CDF II detector, we observe four Lambda b 0 pi+/- resonances in the fully reconstructed decay mode Lambda b 0-->Lambda c + pi-, where Lambda c+-->pK* pi+. We interpret these states as the Sigma b(*)+/- baryons and measure the following masses: m Sigma b+=5807.8 -2.2 +2.0(stat.)+/-1.7(syst.) MeV/c2, m Sigma b- =5815.2+/-1.0(stat.)+/-1.7(syst.) MeV/c2, and m(Sigma b*)-m(Sigma b)=21.2-1.9 +2.0(stat.)-0.3+0.4(syst.) MeV/c2.     

Spin relaxation measurements using first-harmonic out-of-phase absorption EPR signals: rotational motion effects

A recent survey of nonlinear continuous-wave (CW) EPR methods revealed that the first-harmonic absorption EPR signal, detected 90 degrees out of phase with respect to the Zeeman modulation (V(1)(')-EPR), is the most appropriate for determining spin-lattice relaxation enhancements of spin labels (V. A. Livshits, T. Páli, and D. Marsh, 1998, J. Magn. Reson. 134, 113-123). The sensitivity of such V(1)(')-EPR spectra to molecular rotational motion is investigated here by spectral simulations for nitroxyl spin labels, over the entire range of rotational correlation times. Determination of the effective spin-lattice relaxation times is less dependent on rotational mobility than for other nonlinear CW EPR methods, especially at a Zeeman modulation frequency of 25 kHz which is particularly appropriate for spin labels. This relative insensitivity to molecular motion further enhances the usefulness of the V(1)(')-EPR method. Calibrations of the out-of-phase to in-phase spectral intensity (and amplitude) ratios are given as a function of spin-lattice relaxation time, for the full range of spin-label rotational correlation times. Experimental measurements on spin labels in the slow, intermediate, and fast motional regimes of molecular rotation are used to test and validate the method.     

Cold atomic collisions: coherent control of penning and associative ionization

Coherent control techniques are computationally applied to cold (1 mK相似文献   

Ion diffusion-controlled thermally stimulated processes in X-ray irradiated halide crystals

The ionic and ion diffusion-controlled thermally stimulated relaxation (TSR) processes in CaF 2 , BaF 2 , LiBaF 3 and KBr crystals were investigated above 290 v K by means of the ionic conductivity, ionic thermally stimulated depolarisation current (TSDC) and thermal bleaching techniques. Under a DC field the halide crystals store large ionic space charge. We were able to detect in CaF 2 , BaF 2 , LiBaF 3 and KBr in the extrinsic ionic conductivity region a series of the ionic defect (the interstitial anion and/or anion vacancies - in fluorides; the cation vacancies - in KBr) release stages: 3-6 wide and overlapping ionic TSDC peaks. The correlated data of the ionic TSDC and the F band thermal evidence that above 290 v K the TSR processes are initiated and controlled by the ionic defect thermal detrapping, migration and interaction with the localised electronic and ionic charges and colour centres. The ion diffusion-controlled TSR processes take place in the above halide crystals.     

Precision Zeeman-Stark spectroscopy of the metastable a1[3Sigma+] state of PbO

The metastable a(1)[(3)Sigma(+)] state of PbO has been suggested as a suitable system in which to search for the electric dipole moment of the electron. We report here the development of experimental techniques allowing high-sensitivity measurements of Zeeman and Stark effects in this system, similar to those required for such a search. We observe Zeeman quantum beats in fluorescence from a vapor cell of PbO, with shot-noise limited extraction of the quantum beat frequencies, high counting rates, and long coherence times. We argue that improvement in sensitivity to the electron electric dipole moment by at least 2 orders of magnitude appears possible using these techniques.     

Unusual proton Zeeman spin relaxation in an organic solid: several crystal polymorphs or different glass structures?

Solid state proton Zeeman relaxation rate R_1z measurements in two isomers of an organic solid (1- and 2-ethylnaphthalene) are reported. The samples are liquids at room temperature and the temperature T and Larmor frequency ω dependence of R_1z depends strongly on how the sample is solidified. Methyl group (CH₃) rotation is responsible for the proton spin relaxation and the methyl groups serve as probes of the local environment. The R_1z measurements clearly distinguish between different solid states due to the differences in local structure at the several-molecule level. The experiments cannot be used to determine the states of these Van der Waals solids although interpreting the relaxation rate data suggests the states are unusual. We propose that these systems might exist in two (2-ethylnaphthalene) or more (1-ethylnaphthalene) polycrystalline polymorphs or that we are observing distinguishable glassy states, or, both. A phase transition is observed in 1-ethylnaphthalene. Variable temperature X-ray studies of organic systems that solidify well below room temperature are difficult, or at least not routine, and proton spin relaxation measurements serve as a convenient starting point for investigating such systems.     

Sympathetic cooling of polyatomic molecules with S-state atoms in a magnetic trap

We present a rigorous theoretical study of low-temperature collisions of polyatomic molecular radicals with (1)S(0) atoms in the presence of an external magnetic field. Accurate quantum scattering calculations based on ab initio and scaled interaction potentials show that collision-induced spin relaxation of the prototypical organic molecule CH(2)(X(3)B(1)) (methylene) and nine other triatomic radicals in cold (3)He gas occurs at a slow rate, demonstrating that cryogenic buffer-gas cooling and magnetic trapping of these molecules is feasible with current technology. Our calculations further suggest that it may be possible to create ultracold gases of polyatomic molecules by sympathetic cooling with alkaline-earth atoms in a magnetic trap.     

Quantum dynamics of ultracold Na+ Na2 collisions

Ultracold collisions between spin-polarized Na atoms and vibrationally excited Na2 molecules are investigated theoretically, using a reactive scattering formalism (including atom exchange). Calculations are carried out on both pairwise additive and nonadditive potential energy surfaces for the quartet electronic state. The Wigner threshold laws are followed for energies below 10(-5) K. Vibrational relaxation processes dominate elastic processes for temperatures below 10(-3)-10(-4) K. For temperatures below 10(-5) K, the rate coefficients for vibrational relaxation (v=1-->0) are 4.8x10(-11) and 5.2x10(-10) cm(3) s(-1) for the additive and nonadditive potentials, respectively. The large difference emphasizes the importance of using accurate potential energy surfaces for such calculations.     

Nuclear spin resonance of (129)Xe doped with O(2)

Spin-lattice relaxation of (129)Xe nuclei in solid natural xenon has been investigated in detail over a large range of paramagnetic O(2) impurity concentrations. Direct measurements of the ground state magnetic properties of the O(2) are difficult because the ESR (electron spin resonance) lines of O(2) are rather unstructured, but NMR measurements in the liquid helium temperature region (1.4-4 K) are very sensitive to the effective magnetic moments associated with the spin 1 Zeeman levels of the O(2) molecules and to the O(2) magnetic relaxation. From these measurements, the value of the D[Sz(2)-(1/3)S(2)] spin-Hamiltonian term of the triplet spin ground state of O(2) can be determined. The temperature and magnetic field dependence of the measured paramagnetic O(2)-induced excess line width of the (129)Xe NMR signal agree well with the theoretical model with the spin-Hamiltonian D=0.19 meV (2.3 K), and with the reasonable assumption that the E[S(x)(2)-S(y)(2)] spin-Hamiltonian term is close to 0 meV. An anomalous temperature dependence between 1.4 K and 4.2K of the (129)Xe spin-lattice relaxation rate, T(1n)(-1)(T), is also accounted for by our model. Using an independent determination of the true O(2) concentration in the Xe-O(2) solid, the effective spin lattice relaxation time (which will be seen to be transition dependent) of the O(2) at 2.3 K and 0.96 T is determined to be approximately 1.4 x 10(-8)s. The experimental results, taken together with the relaxation model, suggest routes for bringing highly spin-polarized (129)Xe from the low temperature condensed phase to higher temperatures without excessive depolarization.