Mass-resolved resonance enhanced ionization study of complicated excited electronic states of Rb2 near 430 nm and their predissociation dynamics

We have investigated the Rb2 430 nm system by resonance enhanced two-photon ionization and photofragment yield spectroscopy. Four electronically excited states have been assigned, and their two-channel (fast and slow) predissociation has been observed. For the 3 1Piu, 3 1Sigmau+, 3 3Piu(0u+), and 3 3Piu(1u) states, electronic term values (Te) and vibrational constants (omegae and omegaexe) have been determined. For the predissociation dynamics, we have observed the fast predissociation threshold between the isotopically shifted 3 1Piu v' = 14 levels of 85Rb2 and 85Rb87Rb where the 4 2D5/2 + 5 2S1/2 atomic fine-structure limit is located. The 1 3Deltau state corresponding to the 4 2D5/2 + 5 2S1/2 atomic fine-structure limit has been assigned to the predissociating perturber responsible for the fast channel. Also, we have found that the fast channel branches out into two finer product channels due to long-range potential crossing.     

Tuning ab initio data to scattering length: the a (3)Sigma(+) state of KRb

Interaction energies for the lowest triplet state a (3)Sigma(+) of KRb are calculated using high level ab initio methods. The interaction energies are then morphed so that the resulting potential energy curve yields 32 bound states and the correct scattering length for (40)K(87)Rb. Calculated vibrational spacings are shown to be in very good agreement with the available experimental Fourier transform and photoassociation vibrational data, but a different numbering scheme has to be used for the experimental vibrational assignment.     

Full dimension Rb2He ground triplet potential energy surface and quantum scattering calculations

We have developed a three-dimensional potential energy surface for the lowest triplet state of the Rb(2)He complex. A global analytic fit is provided as in the supplementary material [see supplementary material at http://dx.doi.org/10.1063/1.4709433 for the corresponding Fortran code]. This surface is used to perform quantum scattering calculations of (4)He and (3)He colliding with (87)Rb(2) in the partial wave J = 0 at low and ultralow energies. For the heavier helium isotope, the computed vibrational relaxation probabilities show a broad and strong shape resonance for a collisional energy of 0.15 K and a narrow Feshbach resonance at about 17 K for all initial Rb(2) vibrational states studied. The broad resonance corresponds to an efficient relaxation mechanism that does not occur when (3)He is the colliding partner. The Feshbach resonance observed at higher collisional energy is robust with respect to the isotopic substitution. However, its effect on the vibrational relaxation mechanism is faint for both isotopes.     

Formation of ultracold Rb2 molecules in the v' = 0 level of the a(3)Σ+(u) state via blue-detuned photoassociation to the 1(3)Π(g) state

We report on the observation of blue-detuned photoassociation in Rb(2), in which vibrational levels are energetically above the corresponding excited atomic asymptote. (85)Rb atoms in a MOT were photoassociated at short internuclear distance to levels of the 1(3)Π(g) state at a rate of approximately 5 × 10(4) molecules s(-1). We have observed most of the predicted vibrational levels for all four spin-orbit components; 0(+)(g), 0(-)(g), 1(g), and 2(g), including levels of the 0(+)(g) outer well. These molecules decay to the metastable a(3)Σ(+)(u) state, some preferentially to the v' = 0 level, as we have observed for photoassociation to the v' = 8 level of the 1(g) component.     

Nuclear electric quadrupole moments of Rb from the hyperfine spectrum of RbF

The molecular beam electric resonance technique has been used to examine the hyperfine spectrum of RbF. The Rb nuclear electric quadrupole interaction, the spin-rotation interactions, and tensor and scalar spin-spin interactions have been measured for both Rb isotopes, including their dependence on vibrational and rotational states. Transition frequencies have been determined to a precision of better than 1 Hz in many cases. The magnetic interactions in the two isotopomers are consistent with what is expected from the known masses and magnetic dipole moments. In the case of the Rb nuclear electric quadrupole interaction, adjustments have been made for a small isotopomer shift, and for the ratio of the effective nuclear electric quadrupole moments, Q(87Rb)Q(85Rb) = 0.483 830 1+/-0.000 001 8. The effective quadrupole interaction includes a pseudoquadrupole interaction that may be significant at this level of precision, but cannot be distinguished experimentally.     

Isotope shifts in spectral lines of Yb+ in 322-615nm region and term shifts of odd and even parity energy levels of Yb II

Isotope shift Δσ(¹⁷²Yb - ¹⁷⁶Yb) has been measured in 79 classified lines of Yb II in the region 3225-6155 Å. Earlier studies provide isotope shift data in just six lines of Yb II. Term isotope shift ΔT (¹⁷²Yb-¹⁷⁶Yb) have been evaluated for 38 even and 30 odd parity levels of Yb II, using the present isotope shift data. The ΔT values have been discussed and correlated with the purity of the configuration assigned to an energy level, which enabled to check the reported eigenvector percentages of different configurations for some of the levels of Yb II. ΔT values of different levels resulting from J_IL_II couplings are also discussed.     

Vibrational relaxation and dephasing of Rb2 attached to helium nanodroplets

The vibrational wave-packet dynamics of diatomic rubidium molecules (Rb(2)) in triplet states formed on the surface of superfluid helium nanodroplets is investigated both experimentally and theoretically. Detailed comparison of experimental femtosecond pump-probe spectra with dissipative quantum dynamics simulations reveals that vibrational relaxation is the main source of dephasing. The rate constant for vibrational relaxation in the first excited triplet state 1(3)Σ(g)+ is found to be constant γ ≈ 0.5 ns(-1) for the lowest vibrational levels v ? 15 and to increase sharply when exciting to higher energies.     

Insights into the structures, energetics, and vibrations of aqua-rubidium(I) complexes: ab initio study

We have carried out ab initio and density functional theory calculations of hydrated rubidium cations. The calculations involve a detailed evaluation of the structures, thermodynamic properties, and IR spectra of several plausible conformers of Rb+ (H2O)(n=1-8) clusters. An extensive search was made to find out the most stable conformers. Since the water-water interactions are important in hydrated Rb+ complexes, we investigated the vibrational frequency shifts of the OH stretching modes depending on the number of water molecules and the presence/absence of outer-shell water molecules. The predicted harmonic and anharmonic vibrational frequencies of the aqua-Rb+ clusters reflect the H-bonding signature, and would be used in experimental identification of the hydrated structures of Rb+ cation.     

Calculation of highly excited vibrational states using a Richardson-Leja-Davidson scheme

An efficient computational scheme for calculating highly excited vibrational eigenstates is proposed, combining a Richardson-Leja spectral filter with a novel version of the Davidson method [J. Comput. Phys. 17, 87 (1975)]. Highly excited eigenstates of the Rb2 and H2O molecules are computed to test and verify the method. On the average less than 2.5 outer recursions per eigenstate are needed. For each outer Davidson recursion, less than 20 inner filter recursions per eigenstate are needed on the average.     

Observation of the 3(3)Sigma(+)-X1Sigma+ transition of KRb by resonance enhanced two-photon ionization in a pulsed molecular beam: Hyperfine structures of 39K85Rb and 39K87Rb isotopomers

The 3(3)Sigma(+)-X1Sigma+ transition of KRb is observed by resonance enhanced two-photon ionization in a pulsed molecular beam. Hyperfine splittings of 39K85Rb and 39K87Rb isotopomers are observed. From the magnitude of hyperfine splittings, we found that the main hyperfine structure was dominated by the Fermi contact interaction between the Rb nuclear spin and the unpaired electron spin. The Fermi contact interaction constants were determined to be 291 MHz for 39K85Rb and 665 MHz for 39K87Rb. In the KRb 3(3)Sigma+ state the electron spin couples more strongly with the Rb nuclear spin than with other angular momenta, and the energy level structure is well described by the hyperfine angular momentum coupling scheme of the b(betaS) case. The molecular constants and the Rydberg-Klein-Rees potential energy curve of the 3(3)Sigma+ state were determined.     

Radiative transition probabilities, lifetimes and dipole moments for the vibrational levels of the X1Sigma+ ground state of 39K85Rb

Using a potential energy curve (based primarily on the RKR potential of Amiot and Verges [J. Chem. Phys. 112, 7068 (2000)]) and a dipole moment function (based primarily on ab initio calculations of Park et al. [Chem. Phys. 257, 135 (2000)]), we have calculated radiative transition probabilities (Einstein A coefficients), radiative lifetimes, and dipole moment expectation values involving all vibrational levels (for several rotational quantum numbers) of the X1Sigma+ ground state of 39K85Rb. We observe that the radiative lifetimes of vibrationally excited levels, in particular, are approximately 10(3)-10(6) seconds, far too long to be significant in most ultracold experiments involving 39K85Rb or its isotopomers. Comparison with other molecules (LiH and HF) suggests that simple scaling (A approximately mu2nu3 approximately tau(-1)) will predict similarly long lifetimes for many other heteronuclear molecules, e.g., RbCs.     

77Se and 87Rb Solid state NMR study of the structure of Rb2[Pd(Se4)2].Se8

The structure of Rb(2)[Pd(Se(4))(2)].Se(8) has been investigated using (87)Rb magic angle spinning and static NMR and (77)Se magic angle spinning NMR. The number and the integrated intensities of the (87)Rb and (77)Se resonances are in full agreement with the crystallographic structure of the compound. The (87)Rb and (77)Se nuclear spin interaction parameters have been used to characterize the main structural units of the compound: infinite [Rb(Se(8))](x)(x+) columns and polymeric [Pd(Se(4))(2)](x)(2x-) sheet anions.     

Radiometrische und Analytische Ausnützung der Natürlichen Instabilität von87Rb

Possibilities of radiometric determination of Rb in liquid and solid samples using⁸⁷Rb are discussed. In spite of the relatively low β-ray energy of⁸⁷Rb, it is possible to achieve relatively high total counting efficiency (up to 75%) using gas flow GM counters. This fact makes possible to use the natural instability of⁸⁷Rb also for the purposes of calibration. In this paper the conditions of radiometric determination mainly of small amounts of Rb are described (minimum measurable amount is 0.07% of Rb).⁸⁷Rb can be used for the minimum activity determination by measuring β-radiation in the interval of energy of 0.27 MeV.      

Schwingungsspektren und Kraftkonstanten der Elpasolithe Cs2KMF6 (M = Sc,Y, La,Gd, Yb)

Vibrational Spectra and Force Constants of the Elpasolites Cs₂KMF₆ (M = Sc, Y, La, Gd, Yb) The vibrational spectra of the elpasolites Cs₂KMF₆ (M = Sc, Y, La, Gd, Yb) have been recorded and assigned including the lattice vibrations. The vibrational frequencies thus obtained were used for the calculation of XVFF force constants. The values of the stretching force constants are discussed.     

87Rb electron spin resonance on helium nanodroplets: the influence of optical pumping

Hyperfine resolved electron spin resonance (ESR) measurements of single rubidium ((87)Rb) atoms isolated on superfluid helium nanodroplets are presented. In accordance with our previous work on (85)Rb, we find a relative increase of the hyperfine constant a(HFS) by about 400 ppm, depending on the size of the droplets. In order to optimize the ESR signal intensities, the processes of optical pumping of Rb atoms on helium droplets and of optical detection of the ESR transitions are investigated in detail. Both the laser intensity and polarization influences the ESR signal intensities. A simple model for optical pumping of Rb atoms on helium droplets is presented, which agrees well with the experimental results.     

Cooperative near-IR to visible photon upconversion in Yb3+-doped MnCl2 and MnBr2: comparison with a series of Yb3+-doped Mn2+ halides

Yb3+-doped MnCl2 and MnBr2 crystals exhibit strong red upconversion luminescence under near-infrared excitation around 10 000 cm(-1) at temperatures below 100 K. The broad red luminescence band is centred around 15 200 cm(-1) for both compounds and identified as the Mn2+ 4T1g-->6A1g transition. Excitation with 10 ns pulses indicates that the upconversion process consists of a sequence of ground-state and excited-state absorption steps. The experimental VIS/NIR photon ratio at 12 K for an excitation power of 191 mW focused on the sample with a 53 mm lens is 4.1% for MnCl2:Yb3+ and 1.2% for MnBr2:Yb3+. An upconversion mechanism based on exchange coupled Yb3+-Mn2+ ions is proposed. Similar upconversion properties have been reported for RbMnCl3:Yb3+, CsMnCl3:Yb3+, CsMnBr3:Yb3+, RbMnBr3:Yb3+, Rb2MnCl4:Yb3+. The efficiency of the upconversion process in these compounds is strongly dependent on the connectivity between the Yb3+ and Mn2+ ions. The VIS/NIR photon ratio decreases by three orders of magnitude along the series of corner-sharing Yb3+-Cl--Mn2+, edge-sharing Yb3+-(Cl-)2-Mn2+ to face-sharing Yb3+-(Br-)3-Mn2+ bridging geometry. This trend is discussed in terms of the dependence of the relevant super-exchange pathways on the Yb(3+)-Mn2+ bridging geometry.     

Instrumental neutron activation analysis for multi-elemental determination in Indian tea samples

Instrumental neutron activation analysis (INAA) was employed to determine concentrations of 19 elements (As, Ba, Br, Ce, Co, Cr, Cs, Fe, K, La, Mn, Na, Nd, Rb, Sc, Sm, Th, Yb and Zn) in a large number (55) of tea samples (from market as well as virgin tea leaves) from different locations in India (Assam, Darjeeling, Munnar and Kangra). The results obtained in the present work are compared with those reported in literature. The concentration levels, their variations with collection locations and the correlations among different elements in these samples are discussed.     

Theoretical studies on the optical spectra and EPR parameters for trigonal Yb3+ center in CsCdBr3 crystal

In this paper, the crystal-field energy levels, the EPR g factors g//, g(perpendicular) of Yb3+ and hyperfine structure constants A//, A(perpendicular) of 171Yb3+ and 173Yb3+ isotopes in CsCdBr3 crystal are calculated from the crystal-field theory. The calculated results (seven energy levels and six EPR parameters) are in reasonable agreement with the observed values. In the calculation, we find that Yb3+ ion does not occupy the exact Cd2+ site, but is shifted from the center of bromine octahedron by a distance (Delta)Z approximately 0.184 angstroms along C3 axis. The results are discussed.     

The use of sector field ICP-mass spectrometry for Rb-Sr geochronological dating

Rb-Sr dating, one of the most important tools in geochronology, requires determination of the Rb/Sr concentration ratios and the 87Sr/86Sr isotope ratios in co-genetic minerals or rocks and is traditionally performed by thermal ionization mass spectrometry (TIMS). In this work we investigated whether sector field inductively coupled plasma mass spectrometry (ICP-MS), which is characterized by a high sample throughput and straight-forward sample introduction, could be used as an alternative to TIMS. To avoid spectral overlap of the ion signals of the isobaric nuclides 87Sr and 87Rb, Sr was separated from Rb by cation-exchange chromatography. A mathematical correction was applied to take into account the small amount of Rb that can be present in the Sr fraction. The isotope ratio accuracy and precision attainable with ICP-MS were evaluated by analysis of several reference materials from the US Geological Survey. The results of this evaluation show that excellent accuracy could be achieved; the internal precision (repeatability) of the isotope ratio (expressed as the relative standard deviation for 10 successive 1-min measurements) was 0.04-0.12%. An attempt was made to calculate the total or combined uncertainty on the isotope ratio results, by also taking into account other possible error sources (corrections for mass discrimination, detector dead time, blank signal and Rb fraction). Finally, the same procedure was used for dating two rock formations that were 2,500 Ma and 350 Ma old, according to age determinations previously performed by the Rb-Sr laboratory of the University of München (Germany) using TIMS. The ICP-MS results (2,520 +/- 150 Ma and 379 +/- 48 Ma) obtained for these formations compare well with the corresponding TIMS data (2,509 +/- 120 Ma and 357 +/- 25 Ma).