Collisions of metastable Ne*, He* atoms with ground-state He,Ne atoms studied by atomic beam and laser techniques

A crossed nozzle-beam experiment is used to investigate thermal energy collisions: Ne*(2p ⁵3s,³ P _{0, 2})+He(1s ²,¹ S ₀), almost purely elastic, and He*(1s2s,^{1, 3} S)+Ne(2p ⁶,¹ S ₀), in which inelastic excitation transfers occur. State and velocity selection of the scattered Ne* atoms is performed using a tunablecw dye laser frequency locked on a definite Zeeman component of the transition 1s ₅→2p ₆ (λ=614.3 nm) of²⁰Ne or²²Ne. In the purely elastic case, this technique allows the selection of one of the two final velocities, and then an unambiguous LAB-CM transformation. The differential cross section at 62 meV tallies on accords with a calculation using a single effective potential. In He* on Ne collisions, the main inelastic processes are endothermic excitation transfers from He*(2¹ S). Experimental results obtained at different energies (62, 95, 109, 124 meV) show that the transfers essentially result in levels 3s and 4d of Ne.     

Hartree-fock energies ofL,S multiplets of open-shell Nan-type jellium spheres

Numerical Hartree-Fock calculations on the^2S+1 L states arising from 1s ² 1 p^v and 1s ² 1p ⁶ 1 p^μ open-shell configurations of Na_n-type (n≦20) jellium spheres are reported for the first time. TheL, S multiplet energy spread is substancially larger than that expected from earlier estimates of exchange interaction energies. A new way of considering cluster abundance structures in mass spectra emerges from the results.     

On the hyperfine structure and isotope shift of radium

The hyperfine structure and isotope shift of the heaviest known alkaline earth element radium (Z=88) have been studied in both the atomic Ra I and ionic Ra II spectra. The measurements, carried out by on-line collinear fast-beam laser spectroscopy, yield the hyperfine constantsA andB of the 7s and 7p _1/2 states in Ra II, of all states of the excited 7s 7p configuration and the 7s 7d ³ D ₃ state in Ra I. The data allow a consistent evaluation of the nuclear moments for eight odd-A radium isotopes. In particular, a complete analysis of the hyperfine structure of thesp configuration in the two-electron system provides a stringent test of the validity of the semi-empirical modified Breit-Wills theory. It is shown that the effective operator formalism is equivalent, if relativistic correction functions are used to reduce the number of parameters. The semi-empirical hyperfine fields are evaluated and found to agree generally with those from ab-initio calculations. The isotope shifts in thes?p,s ²?sp,sp?sd transitions are analysed semi-empirically and compared with ab-initio calculations. The consistency of the different analyses proves their validity and classifies the spectrum of Ra I as a model case for a simple and clean two-electron spectrum.     

Relativistic calculation of Stokes' parameters for intermediate energy electron impact excitation of cesium atoms

The integrated and differential Stokes' parameters of the light emitted in the decay 6p ² P _1/2,3/2→6s ² S _1/2 fore-Cs scattering in the intermediate energy range are presented. These have been calculated using scattering amplitudes obtained by a relativistic distorted-wave method.     

Hyperfine structure and isotope shift of some even parity levels in the YbI spectrum

Using laser induced fluorescence spectroscopy the hyperfine structure of the even parity levels 4f ¹⁴6s6d ³ D ₁, 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 as well as of the odd parity level 4f ¹⁴ 6s6p ³ P ₂ in neutral ytterbium has been investigated. The isotope shift of the transitions 4f ¹⁴6s6p ³ P ₀ → 4f ¹⁴ 6s6p ³ D ₁ and 4f ¹⁴ 6s6p ³ P ₂ → 4f ¹⁴ 6s8s ³ S ₁, 4f ¹³ 5d6s6p (7/2, 5/2)J=1,2,3 could be measured with high accuracy. The results for the 4f ¹⁴ 6s6p ³ D ₁ level show a considerable influence of second order effects of the hyperfine interaction. The isotope shifts of the 4f ¹⁴ 6s8s ³ S ₁ and 4f ¹³ 5d6s6p (7/2, 5/2)J=1 levels indicate a possible configuration mixing for these levels.     

Investigations of radiative lifetimes in the 3p5p configuration of neutral silicon

Lifetimes for the³ S ₁,³ P _{0, 1, 2} and³ D _{1, 2, 3} states in the 3s ²3p5p configuration of silicon have been determined using stepwise dye laser excitation and time resolved detection. A comparison is made with theoretical values, calculated using multi-configuration Hartree-Fock wavefunctions. Laser-evaporation was used to produce free silicon atoms by focusing a Nd: YAG laser on a rotating silicon target.     

Alignment of double vacancy states (1s2p)−1 3 P and1 P of neon for electron impact ionization

From intensity of Auger transitions (1s2p)^{?1 1} P,³ P→2p ^{?3 2} P,² D+e _A ^? relative to 1s ^{?1 2} S→2p ^{?2 1} D+e _A ^? measured at ?=54 and 90° relative to the primary electron beam we have determined the alignment of double vacancy states (1s 2p)^{?1 1} P and³ P of neon for electron impact ionization for the impact energies 1.5, 2.0, 2.5 and 4.0 keV. ForE ₀=1.5, 2.0 and 2.5 keV the alignment is compatible with zero with an upper limit of , forE ₀=4.0 keV a small negative value was found.     

Precision energies and hyperfine structures of the 5s5p 3 P 0,1,2 0 and 5s6s 3 S 1 levels in In II

Absolute frequencies of hyperfine components of the 230.6 nm (5s ^{2 1} S ₀?5s5p ³ P ₁ ⁰ ), 193.6 nm (5s5p ³ P ₀ ⁰ ?5s6s ³ S ₁), 197.7 nm (5s5p ³ P ₁ ⁰ ?5s6s ³ S ₁) and 207.9 nm (5s5p ³ P ₂ ⁰ ?5s6s ³ S ₁) transitions in In II emitted from a hollow-cathode source have been measured using a high-resolution, scanning échelle monochromator. The measured frequencies of these four transitions have been used to determine the energies and hyperfine interaction constants of the 5s5p ³ P ₀ ⁰ ,³ P ₁ ⁰ ,³ P ₂ ⁰ and 5s6s ³ S ₁ levels in In II. The hyperfine interaction constants for the dominant isotope¹¹⁵In are found to be: 5s5p ³ P ₁ ⁰ A=0.2322(2) cm^?1,B=?0.0159(9) cm^?1 5s5p ³ P ₂ ⁰ A=0.1699(4) cm^?1,B= 0.021 (6) cm^?1 5s6s ³ S ₁ A=0.4022(4) cm^?1,B= 0.002 (2) cm^?1. The absolute frequency of the very narrow, strongly forbidden In II 236.5 nm (5s ^{2 1} S ₀?5s5p ³ P ₀ ⁰ ) transition, which has been proposed as a candidate for a new optical frequency standard, is found to be 42275.986(7) cm^?1.     

Intercombination lines of Mg I-, Al I- and Si I-like ions in the beam foil spectra of Ti,Fe, Ni and Cu

In delayed spectra of foil-excited beams of Ti, Fe, Ni and Cu ions lines have been observed which are identified with intercombination transitions 3s ^{2 1} S ₀ — 3s 3p ³ P ₁ ⁰ , 3s ² 3p ² P ⁰ — 3s 3p ^{2 4} P and 3s ² 3p ^{2 3} P — 3s 3p ^{3 5} S ₂ ⁰ in magnesiumlike, aluminiumlike and siliconlike spectra, resp. Wavelengths and decay properties have been determined. The results are compared to recent theoretical predictions.     

Stark-mixing effect on the 6p 2 1 S 0−6p 2 3 P 2 transition in Pb I

The intensity of the 531.5 nm electric-field-quench radiation has been measured on a thermal beam of neutral Pb atoms in the metastable 6p ^{2 1} S ₀ state. The measurement yields a Stark-mixing amplitude for transition between the 6p ^{2 1} S ₀ and 6p ^{2 3} P ₂ states. Combining this result with available experimental data sets an upper limit for the 6p 7s ³ P ₁ → 6p ^{2 1} S ₀ transition probability:A _ki <1.79·10³ s ^?1. Calculations for the 6p 7s → 6p ² and 6p 8s → 6p ², as well as transition rates of forbidden lines inside 6p ² configuration of PbI are presented and compared with existing experimental data.     

Lifetime measurements and stark mixing of autoionizing Cu I-states

Using a combination of collisional and laser excitation the lifetimes of 17 autoionizing Cu I states in the configurations 3d ⁹ 4s 6s and 3d ⁹ 4s4d were measured. The lifetimes are in the range of 1–50 ps and depend strongly on the coupling properties, the mixing with different configurations, and the radial integrals of the discrete with the continuum states. For the level 3d ⁹ 4s 4d ⁴ S _3/2 the influence of an electric field via Stark mixing of 3d ⁹ 4s 5p ⁴ P _1/2 on the autoionizing rate was investigated. The experimental values are compared with theoretical results which follow from ab initio calculations for the transition probabilities and least square fit values deduced from the experimental positions. Good agreement is found only for theJ=3/2 levels of both configurations 3d ⁹ 4s 4d and 3d ⁹ 4s 6s.     

Avoided level crossings in bound Rydberg states of barium in an electric field

In a CW laser experiment on bound Rydberg states of barium electric-field-induced level crossings were studied. A regular type of avoided crossing of 6snf ³ F ₂ and 6s (n+4)s ³ S ₁ levels (n≈60,M=0) was observed under circumstances where the minimum separation was larger than the linewidth involved. This type of crossing could be reproduced using a diagonalisation procedure of the total energy matrix in the presence of the field. However, in the case of avoided crossings of the 6snf ³ F ₂ and 6s(n+4)p ¹ P ₁ sublevels, where the minimum separation was smaller than the linewidth of the³ F ₂ level, an interference-like profile was recorded. An important feature in the explanation of this interference-like profile turned out to be the broadening of the³ F ₂ level by small field inhomogeneities.     

Isotope Shifts of Nitrogen around 800 nm

The Doppler-limited absorption spectra of ¹⁴N and ¹⁵N atoms were measured around 800 nm using concentration modulation spectroscopy to study their isotope shifts. The nitrogen atoms were generated by discharging molecular nitrogen buffered with helium in a homemade discharge tube. The isotope shifts of four multiplets (3s⁴P_J→3p⁴D_J^o, 3s⁴P_J→3p⁴P_J^o, 3s²D_J→5s²P_J^o, and 3p²P_J^o→5s²D_J^o) were measured and their J-dependent specific mass shifts were observed and discussed.     

Velocity dependence of impact line-broadening studied by resonant doppler-free two-photon laser spectroscopy

The velocity dependence of the collison broadening of the⁴⁰Ca 4s ^{2 1} S ₀→4s5p ¹ P ₁ →4s17d ¹ D ₂ transition by neon atoms has been studied. The experiment was performed exciting one velocity group of Ca atoms within the Doppler profile of the first transition and probing this group with a counterpropagating laser beam inducing the second transition. Using thermionic detection we have measured broadening rates for relative velocities between Ca and Ne atoms which corresponds to a temperature range of about 850 K (cell temperature) to 3000 K. The measured line-width was found to have very weak temperature dependence. This is attributed to the weak velocity dependence of polarization broadening of the final level which was found to be the major contribution to the broadening of the two-photon line. For large relative velocities significant asymmetries in the measured line profiles due to velocity changing collisions had to be taken into account.     

The nickel-group IV molecules NiC,NiSi, and NiGe

All electron ab initio calculations have been applied to elucidate the electronic states and the nature of the chemical bonds in the molecules NiC, NiSi, and NiGe. The calculations have revealed that the ground states of all three molecules are¹Σ⁺, but due to the open 3d shell of the Ni atom the molecules have many low-lying electronic states. The NiC molecule is strongly polar, and the low-lying electronic states have been identified as those arising when the angular momenta of the³F_g Ni⁺ ion are coupled to the angular momenta of the⁴S_uC^? anion. The chemical bond in the NiC molecule has triple bond character due to the valence bond couplings between the Ni 4s and 3dπ electrons and theC 2p electrons. The chemical bonds in the molecules NiSi and NiGe are very much alike; they are double bonds composed of oneσ and oneπ bond. Theσ bond is due to the doubly occupied delocalized molecular orbital composed of the Ni 4s orbital and the Si 3pσ or the Ge 4pσ orbital. Theπ bond originates from the valence bond coupling between the localized hole in the Ni 3dπ orbital and the valencepπ electron of Si or Ge.     

Spin-resolved orientation,depolarization and left-right asymmetry in electron-lithium scattering

A two-potential localised exchange (TPLE) approach is used to study the role of spin dependence in the inelastic scattering of electrons by lithium atoms at intermediate energies. Results are presented for the spin-resolved orientation parameters (L _⊥ ^S ,L _⊥ ^T , andL _⊥) in the polarized-electron impact resonant (2s–2p) excitation of polarized-lithium atom. Results are also obtained for the depolarization (P′ _e /P _e) in the polarized-electron impact resonant (2s–2p) and nonresonant (2s–3p) transition in unpolarized lithium atom. Further in the case when the fine structure splitting of the target is resolved, we also investigate the left-right scattering asymmetryS _A (1/2) for the polarized-electron superelastically scattered from unpolarized 2p _1/2 and 3p _1/2 states.     

Natural radiative lifetimes in the2 S 1/2 and2 D 3/2, 5/2 sequences of neutral copper

Natural radiative lifetimes have been measured of the 3d ¹⁰ ns ² S _1/2 (n=6?10) and of the 3d ¹⁰ nd ² D _{3/2, 5/2} (n=5?9) sequences by using two step excitation of copper atoms in an atomic beam. The states investigated were populated by the light from two pulsed dye lasers pumped by the same Nd:YAG laser. The lifetimes of the² D sequence increase regularly with increasing principal quantum number. This is not the case for the² S series, because of configuration interaction in the² P series. In addition the lifetime of the 3d ¹⁰5p ² P _3/2 state has been measured together with its branching ratio.     

Constructing novel red-emitting Ba2Y0.8Eu0.2NbO6:Mn4+ phosphors for multi-type luminescent thermometers and high-security anti-counterfeiting films

To date, luminescent materials have been preferably used for non-contact optical thermometers. In this manner, novel red-emitting Ba₂Y_0.8Eu_0.2NbO₆:Mn⁴⁺ (BYEN:Mn⁴⁺) phosphors were designed for multi-type non-contact luminescent thermometers based on the dual-emission states and temperature-dependent lifetime (TDL) models. In the temperature range of 303–483 K, the sensing sensitivities based on the dual-emission states of (⁵D₀→⁷F₂, ²E_g→⁴A_2g) and (⁵D₀→⁷F₁, ²E_g→⁴A_2g) were estimated. Especially, the maximum absolute sensing sensitivity (S_a) was found to be about 0.1558 K^-1 for the BYEN:0.007Mn⁴⁺ phosphor based on the ⁵D₀→⁷F₁ and ²E_g→⁴A_2g positions. This phosphor also exhibited good relative sensing sensitivity (S_r) (0.0186 K^-1) based on the ⁵D₀→⁷F₂ and ²E_g→⁴A_2g states. Besides, the relative sensing sensitivities (S_R) at ⁵D₀→⁷F₁ and ²E_g→⁴A_2g transitions were estimated to be 0.0034 and 0.0194 K^-1, respectively with the help of the TDL technique. In the light of these results, novel red-emitting Ba₂Y_0.8Eu_0.2NbO₆:Mn⁴⁺ phosphors are expected to be a potentially attractive candidate for applications in multi-type luminescent thermometers. Finally, a novel unique polydimethylsiloxane film exhibiting tricolor-luminescent emissions was introduced and further suggested for high-security anti-counterfeiting.     

Experimental and theoretical investigation of radiative lifetimes in neutral gallium

Using laser spectroscopic techniques the natural radiative lifetimes of 4s ² n ₁ s ² S and 4s ² n ₂ d ² D states of neutral gallium have been measured forn ₁ = 6 to 11 andn ₂ = 4 to 9. These states, as well as previously measured4s ² np ² P states, have been investigated theoretically using multi-configuration Hartree-Fock calculations. Oscillator strengths to all lower-lying states have been calculated and theoretical lifetimes of the investigated states evaluated. The² D sequence is strongly influenced by the 4s4p ^{2 2} D perturber, and strong cancellation effects in the radiative decay are observed both theoretically and experimentally.     

Isotope shifts and hyperfine structures investigation of doubly excited levels in SrI

We measured isotope shifts and hyperfine structure of visible transitions of stable strontium isotopes by means of Doppler-free saturated absorption spectroscopy. In particular, we investigated transitions between excited states where the upper level involves two excited electrons. We report hyperfine coupling constants for the levels 5p4d¹D₂, 5p4d³F₂, 5s4d³D₁, 5s6s³S₁, 5s5p³P₁ and, for some of the studied transitions, we separate the specific mass and volume contribution to the isotope shifts.