State Of Na Research Articles

Laser induced fluorescence and high resolution Fourier transform spectrometry

Laser induced fluorescence was first used in conjunction with a high resolution Fourier transform interferometer to study molecular spectra in the early 1980s. Typical examples of such work are cited in this paper to illustrate the high capabilities of this technique. We have focused on comprehensive spectroscopic analyses (I 2, double minimum 1 Σ u + state of Na 2, BaCl, CuCl 2), molecular long range behaviour (I 2, CsH, Li 2), hyperfine structure and collisional rate relaxations (I 2), large variation of the electronic transition moment (I 2), rate determination in an electronic collisional energy transfer (Li 2) and time resolved high resolution Fourier transform spectroscopy.

Systematic study of (Na n )2 dimer transient state in Na n +Na n collisions (n=8, 9, 19, and 20)

From distance dependent tight-binding molecular dynamics simulations, we systematically study the Nan+Nan collision dynamics around the first two closed shells (n=8 and 20). We investigate the stability of sodium cluster dimers (Nan)2, for many events with random relative orientation at finite temperature, various impact parameters and incident energies. We find that (Na8)2, (Na9)2, (Na19)2 and (Na20)2 can exist during about 3000 fs in central collisions while they can exist up to about ten thousands fs in peripheral collisions with larger impact parameters in fusion mechanism at c.o.m energy per atomEcm/n=0.025 eV. We observe that the lower the incident energy, the longer the lifetime of the cluster dimers in both central and peripheral collisions. There is no apparent difference in the dynamical stability of (Na8)2 and (Na9)2, (Na19)2 and (Na20)2 although (Na8)2 and (Na20)2 are respectively slightly colder than (Na9)2 and (Na19)2 for the same incident energy per atom and the same impact parameter.

Proposed modification of the criterion for the region of validity of the inverse-power expansion in diatomic long-range potentials

A modified internuclear distance criterion, R LR- m , as the lower bound for the region of validity of the inverse-power expansion of the diatomic long-range potential is proposed. This new criterion takes into account the spatial orientation of the atomic orbitals while retaining the simplicity of the traditional Le Roy radius, R LR for the interaction of S state atoms. Recent experimental and theoretical results for various excited states in Na 2 suggest that this proposed R LR- m is an appropriate generalization of R LR.

Optical-Optical Double-Resonance Excitation Spectra of the (6 d) 1Δ g and (7 d) 1Δ g Rydberg States in Na 2

The levels with ν ≤ 14, 27 ≤ J ≤ 57 in the (6 d) 1Δ g and (7 d) 1Δ g Rydberg states of Na 2 have been observed using optical-optical double resonance (OODR) fluorescence excitation spectroscopy. The intermediate levels in the B 1Π u state are identified by numerical calculations with the molecular constants for B 1Π u ← X 1Σ + g transitions and confirmed by the complementary A 1Σ + u ← X 1Σ + g polarization spectra. Absolute vibrational numberings of the (6 d) 1Δ g and (7 d) 1Δ g states are determined by comparing the observed OODR excitation intensities of transitions 1Δ g ← B 1Π u with that of the simulated Franck-Condon factors. The Dunham coefficients and the Rydberg-Klein-Rees (RKR) potential energy curves of the (6 d) 1Δ g and (7 d) 1Δ g states are reported.

Optical-Optical Double Resonance Spectroscopy of the 2 1Π g State of Na 2 Using an Ultrasensitive Ionization Detector

Using optical-optical double resonance and an ultrasensitive ionization detector, we have been able to extensively study a wide range of internuclear distances for the 2 1Π g state of Na 2. A total of 80 vibrational levels (0 ≤ v ≤ 43 are from previous work using filter-PMT detection) which covered more than 99.9% of the well depth were observed in this state. The Rydberg-Klein-Rees (RKR) potential energy curve was constructed with a maximum outer turning point R 79+ = 18.08 Å. The potential curve at long range, where it can be described in terms of C n coefficients, is also discussed.

NONCHARGE TRANSFER, DIMERIZATION, AND ELECTRON LOCALIZATION EFFECTS IN ALKALI-DOPED C60

In this work we argue that Na 3 C 60 is an insulator because the Na+ cations recapture their valence electrons forming one center electronic bound state in the fulleride medium. In the A 4 C 60 compounds the alkali atoms should approach each other in pairs forming alkali dimer states. A 4 C 60 is therefore a noncharge transfer insulator and is nonsuperconducting. Finally we conjecture that there may exist Na 2 states in Na 6 C 60.

Angular distribution of photoelectrons in resonant photoionization of polarized atoms

The angular distribution of photoelectrons produced by excitation of polarized atoms to autoionizing states is analysed. In particular, core-excited autoionizing states produced in absorption of synchrotron radiation by laser-pumped excited atoms are considered. A general expression for the angular distribution of arbitrarily oriented laser and synchrotron beams is obtained and further reduced to a simpler form for a particular geometry used in experiments. A case of an isolated autoionizing state (resonance) interacting with several continua is considered and parametrization of the observable parameters in the region of the resonance is discussed. Peculiarities of the circular dichroism in the region of autoionizing resonances are analysed. Formulae suitable for particular resonances with J<or=5/2 are presented and all parameters necessary for analysis of experimental angular distributions are tabulated. As examples, excitations of autoionizing 2p53s3p and 2s3p2 states in Na and 3p53d4s4p states in Ca are considered. Theoretical angular distributions are compared with recent experimental data.

Photoassociative spectroscopy of 1g, 0+u, and 0−g states of Na2

We use photoassociation of ultracold Na to study transitions from free atoms to bound molecules. We obtain rovibrational spectra of the 1g, the 0+u, and, for the first time, the 0−g ‘‘purely long-range’’ state of Na2, all of which dissociate to Na(3 2S1/2)+Na(3 2P3/2).

INTERACTION OF ALKALI METALS WITH SOLID SURFACES STUDIED BY LOW-ENERGY D+ SCATTERING

The study of alkali-metal adsorption on metal and semiconductor surfaces has been a favored topic of surface science. This is motivated by a number of interesting physical effects, such as charge transfer, work function changes, and alteration of surface reactivity. Despite considerable research efforts, however, there has still been significant controversies about most of these properties. In this paper, a review is presented concerning alkali–metal adsorption on well-defined transition-metal and semiconductor surfaces, with particular emphasis on the bond-nature analysis using low-energy D + scattering. The analysis based on resonance neutralization of the D + ions associated with the 1s hole diffusion into the band reveals that Na, K, and Cs adatoms have significant covalency on the transition metal surfaces while those except for Na are ionically adsorbed on the semiconductor surfaces in a small coverage regime (&lt; 1.7 × 1014 adatoms/cm 2). The charge state of Na is rather critical because of the larger ionization energy than the others. The other examples are concerned with the analyses of the interaction of these alkali–metal adatoms with electronegative species such as oxygen and halogens on the metal and semiconductor surfaces.

Erratum: Quenching of low-lying Rydberg states of Na colliding with ground-state He: A semiclassical approach

The molecular expansion method within the framework of the semiclassical approximation is applied to quenching of low-lying excited states of Rydberg atoms colliding with ground-state He at thermal energies. Interactions between the colliding atoms are accounted for in terms of pseudopotentials, and their relative motion is described by a classical linear trajectory. A fairly large basis set of Slater-type orbitals is used to obtain molecular eigenstates, and subsequently a 14-state close-coupling calculation is performed to evaluate the total quenching cross sections and the contributions of individual transitions. The energy dependence of the calculated cross sections is investigated, and possible mechanisms responsible for individual transitions are explained. Finally, the collision rates are calculated and compared with experimental results.

Energy levels and lifetimes for the 2p53snl core-excited states in Na

Systematic calculations of energies and decay rates for the 2p53snl core-excited states (with n<or=7) in Na have been performed using a configuration-interaction method, including spin-orbit interaction and core-polarization correlation through a semi-empirical model core potential. Data obtained extend and clarify considerably the classification of lines in the existing photoabsorption and ejected-electron spectra of Na. Lifetime determination included radiative decay to the bound 2p6nl levels and to the lower core-excited states as well as autoionization. Both correlational and relativistic effects play an important role, as expected, but in addition it was found that the non-orthogonality of bound and continuum orbitals, being a result of core excitation, is also very important in evaluating of autoionization rates. The predicted lifetimes are analysed with respect to their 'quasimetastability', which has recently attracted great attention in atomic spectroscopy and in the construction of XUV lasers.

Time-resolved observation of molecular pseudorotation in Na 3

The temporal behaviour of the pseudorating B state of Na 3 was investigated in a two-photon-ionization (TPI) experiment, employing picosecond laser pulses and a variable delay between the excitation and ionization step. The results exhibit the pseudorotational motion as a temporal sequence. The detailed analysis of the vibronic function time evolution affirms a pdeudo-Jahn—Teller (PJT) model for the interpretation of the B state spectroscopic data.

Optical-optical double resonance spectroscopy of the 1 Sigma g+ "shelf" states and 1 Pi g states of Na2 using an ultrasensitive ionization detector.

Using a shielded cylindrical space-charge-limited diode ionization detector and optical-optical double resonance, the exotic potential energy curves of the 3, 4, 5, and 6 1 Σ g + «shelf» states and 2 and 3 1 Π g states of Na 2 have been extensively studied including levels near dissociation (>99.8% of well depth) with very large outer classical turning points, and long range avoided crossings giving rise to potential «shelfs.» The long range potentials can all be understood and also provide stringently tested high quality theoretical calculations of highly excited states

Spectroscopic Study of the Na 2 2 3Σ +g State by cw Perturbation-Facilitated Optical-Optical Double-Resonance Spectroscopy

The Na 2(3 sσ g )(4 sσ g ) 2 3Σ + g state of Na 2 has been observed and studied by cw perturbation-facilitated optical-optical double-resonance (PFOODR) spectroscopy for the first time. A single-mode dye laser and a Ti-sapphire laser served as the pump and the probe lasers, respectively. A total of 543 PFOODR excitation signals have been assigned to the 2 3Σ + g ← b 3Π 1u transitions. Absolute vibrational numbering was determined by counting nodes in the 2 3Σ + g → a 3Σ + u bound-free spectra. Spectroscopic constants and the corresponding RKR potential energy curve are presented in this vsork. The values of T e, R e, and D e, are found to be 25 551.237(49) cm −1, 3.53463(35) Å, and 6211.5(1) cm −1 respectively.

Femtosecond two-photon ionization spectroscopy of the B state of Na 3 clusters

We report time-resolved experiments studying the dynamics of the Na 3 B—X system. Femtosecond pump-probe techniques combined with ion time-of-flight (TOF) and zero kinetic energy (ZEKE) photoelectron spectroscopy allow us to observe the three-dimensional wavepacket motion in the excited Na 3 B state and in the Na 3 X state. The ground state wavepacket is induced by stimulated emission pumping during the pump pulse. The X-state dynamics is dominated by the three vibrational modes of the Na 3. Furthermore we observed pseudorotational wavepacket motion in the B state. We do not observe a fragmentation of the B state within a time interval of 10 ps.

Unoccupied electronic structure of Na/Ni(111)

Using the technique of inverse photoemission spectroscopy we have measured the unoccupied electronic states of Na on Ni(111) as a function of Na dose on the Ni(111) surface. An image-potential surface state pinned to the vacuum level shifts towards the Fermi level and disappears for Na coverages greater than 0.07 monolayer (ML). This image state reappears at high coverage, when the Na coverage is larger than 0.6 ML and is detected at 2.4 eV above the Fermi level at 1 ML of Na coverage. A Na-induced state which we assign as the Na 3p level appears for Na coverages above 0.02 ML and shifts down towards the Fermi level with increasing coverage. We compare our results with studies of related systems

Observations of the 3(3 d) 3Σ g+ state of Na 2

The 3(3 d) 3Σ g + state of the Na 2 molecule has been observed for the first time by perturbation-facilitated optical-optical double-resonance (PFOODR) excitation spectroscopy through A 1Σ u + ∼ b 3Π u mixed intermediate levels. The rotational structure and the fine-hyperfine splittings of the 3 3Σ g + ← b 3Π u transitions are similar to the 4 3Σ g + ← b 3Π u transitions of Na 2. Absolute vibrational numbering of the 3 3Σ g + state was determined by comparing the experimental excitation intensities with the calculated Franck-Condon factors. Molecular constants and the RKR potential curve are also reported. A comparison of the molecular constants of all eight observed states dissociating to the same 3 s + 3 d asymptote with ab initio theory shows remarkably good agreement.

The (3) 1Π g state of Na 2

The (3) 1Π g state of Na 2

The investigation of metastable states in Na1-xLixNbO3polycrystals near the diffused phase transition

Abstract The dielectric permittivity ϵ of Na1-x Lix NbO3, 0.005<x<0.06, has been measured as the function of temperature (280 K < T < 800 K) and time. The obtained results of dielectric permittivity versus time measured close to the phase transition point were compared to the modified exponential function. The best fit procedures give two values of relaxation times. The second is proposed to be interpreted as related to behaviour of polar clusters surrounding the Li impurities.

The potential of the Na 2 B 1Π u state

The uppermost quasibound rovibrational levels of the B 1Π u state of Na 2 were accessed in a molecular beam experiment using a three step excitation scheme with Franck-Condon pumping and spatially separated laser fields to minimize line profile distortions by nonresonant multi-quantum effects. Level energies and widths due to tunneling are measured accurately. The potential function is directly derived in a fully quantal calculation fitting simultaneously all existing data, levels and widths, on the B state. This approach is superior to the conventional Dunham analysis and needs no more adjustable parameters than the other if a large body of data is involved.