Neon 3p-excitation by proton impact (100 keV-1 MeV): Cross sections and line polarization

The excitation of all ten levels of the neon 2p ⁵3p configuration by proton impact (100 keV-1 MeV) has been investigated by the spectral analysis of photon emission. Absolute emission cross sections have been obtained by calibration with a standard light source. Cascade effects are shown to be very important especially in the case ofJ=1 levels. For the 3p(¹ S ₀) level, which we studied additionally for electron impact excitation (100 eV-1 keV), our experimental cross sections are compared with the first Born approximation. Furthermore the polarization of sixteen 3p—3s emission lines has been measured as a function of impact energy. The energy dependence of the line polarization is characterized by theJ quantum numbers of the atomic states involved in the respective transition. An anomalous polarization of all lines originating from the decay ofJ=1 levels has been found and is referred to dominant cascade effects.     

Lebensdauern und Oszillatorstärken im Sr I- und Ca I-Spektrum

Radiative lifetimes of some highly excited levels in Sr I were measured by zero-field level crossing technique. These levels have been populated using optical excitation starting from the metastable 4d 5s ¹ D ₂ or 5s5p ³ P _2,1,0 states. The high population of these metastable levels necessary for the experiments was obtained by a discharge in the pure Sr vapour burning in the atomic beam oven. The following lifetimes have been determined (in units of 10^?8 sec):τ(5s 6s³ S ₁)=1.09±0.11,τ(5s 5d ³D₁)=1.67±0.10,τ(5s4f¹ F ₃)=3.43±0.28,τ(4d5p ¹ D ₂)=2.19±0.16,τ(5p ^{2 3}P₁)=0.88±0.12,τ(5p ^{2 3} P ₂)=0.78 _?0.10 ^+0.26 . These results are compared with lifetimes derived from oscillator strengths given in the literature, and the reliability of different oscillator strengths tables is discussed. A corresponding discussion is given for radiative lifetimes of some levels in Ca I published previously. Good agreement with data derived from arc emission oscillator strengths has been found. Ca lifetimes are fairly well consistent with oscillator strengths calculated with semiempirical scaled Thomas-Fermi-wave functions.     

Absolute measurement of an atomic cascade rate using a two photon coincidence technique. Application to the 4p21S0 -4s4p 1P1 -4s21S0 cascade of calcium excited by a two photon absorption

The two photon coincidence technique yields an absolute measurement of a cascade decay rate without knowing the detection efficiency of each detector. This method is applied to calcium atoms in an atomic beam excited to the 4p²¹S₀ state, and decaying via the resonant ¹P₁ state; it yields the excitation rate of the upper 4p²¹S₀ level. Since the excitation process (two photon absorption) is controlled, one can compute the excitation rate of the upper level as a function of the transition probabilities in the cascade. The lower transition is well known and we can therefore deduce the transition probability for the 4p²¹S₀ -4s4p ¹P₁, transition which previously had not been accurately determined. The preliminary measurements yield a line strength s = 0.98 ± 0.3 au in good agreement with a recent measurement of the lifetime of the 4p²¹S₀ state.     

Behavior of the excitation cross sections of the perturbed series of the xenon atom

Behavior of the excitation cross sections of the perturbed 6s[3/2]_n°?np[1/2]₀ spectral series of the xenon atom is experimentally studied. By using the methods of extended electron beam and optical spectroscopy, the cross sections are measured and the optical excitation functions are recorded for the transitions of this series with n=6–13. A deviation of the dependence Q=f(n) from a power-law function is revealed, as well as changes in the form of optical excitation functions and in the nature of the branching caused by perturbation of the 7p[1/2]₀ level by levels of the 5p ⁵(² P _1/2°)6p configuration.     

Photothermal ionization via excited states of sulfur donor in silicon

Structures in the photoionization cross-section spectra below the extrinsic edge of the doubly charged sulfur donor (613 meV) are attributed to the two-step photothermal excitation process in which the bound electron at the ground state first makes an optical transition to an excited state and it is then thermally released from the excited state to the conduction band. A weak peak (cross-section 7 × 10⁻¹⁹ cm²)at 425 meV is attributed to the intervalley optical transition 1s(A₁)→1s(T₂). Peak observed at 570 meV (10⁻¹⁷ cm²) is attributed to the 1s(A₁→2p₀ intervalley optical transition and the peak at 591 meV (3 × 10⁻¹⁷ cm²) to the 1s(A₁)→2p± intravalley optical transition. Data for electron bound at the neutral gold center has no structures which is consistent with the lack of excited states of a neutral impurity potential.     

A redetermination of the lifetime of the 4s 5s (3S1) level in Ca by high-rate electron—photon stepwise pulse excitation

The radiative lifetime of the 4s 5s (³S₁) level in Ca was measured using two-step excitation of atoms in a beam which traverses a cold-cathode Penning discharge, where, by electron impact the atoms are excited to the metastable 4s 5p (³P_{2, 1, 0}) states. Immediately thereafter, the beam is crossed with a pulse-modulated cw dye laser beam to populate the final state selectively. Using a pulse-modulation frequency of 0.5 MHz, a preliminary value of 12.4 ± 0.5 ns was obtained with a statistical error of 0.4%. The wide limits of systematic error reflect an assumed uncertainty in the excitation function and possible distortion in the fluorescence decay requiring further study.     

Carbon K-shell excitation spectra of linear and branched alkanes

The electron energy loss spectra of ethane, propane, n-butane, n-pentane, n-hexane, isobutane, isopentane and neopentane in the region of carbon K-shell excitation have been recorded under dipole-dominated conditions (2.8 ke V impact energy, small angle). The spectra are dominated by transitions to unoccupied valence π¹(CH₂, CH₃) and σ¹(C-C) levels. Additional weak features are assigned to Rydberg transitions. The position of the main continuum feature in each spectrum is consistent with the predictions of an empirical relationship with bond length. Systematic variations of spectral intensities are observed which support our assignments. The dominant feature in the K-shell spectrum of ethane, which was previously assigned to C 1s → 3p Rydberg transitions, is reassigned to excitation to a 3p/π¹(CH₃ ), mixed Rydberg/valence orbital (of antibonding σ-¹(C-H) character), in comparison to the other alkane spectra. An improved calibration value of 290.74(5) eV for the energy of the C 1s → π¹ transition in CO₂ is also obtained.     

Population of 2p 55s levels of neon in He-Ne plasma: I. The evolution of mechanisms in the discharge and the afterglow

The spectroscopic study of population processes of neon 2p ⁵5s states was carried out in helium afterglow with small admixture of neon at PHe = 38.1 torr, [He]/[Ne]=10^?5 with pulsed discharge afterglow in helium with small admixture of neon (pressure equal to 38.1 mm Hg; ). It is established that the main mechanism of population of 3s ₂ level (in Paschen’s notation) in the discharge and the initial after-glow is the excitation transfer from metastable atoms of He(2¹ S ₀). The other three levels—3s ₃, 3s ₄, and 3s ₅—corresponding to 2p ⁵5s configuration are populated in the afterglow as a result of the dissociative recombination HeNe⁺ of ions with electrons. The same process is also the main channel of population of 3s ₂ level in the late afterglow phase, when the concentration of He(2¹ S ₀) atoms is small. The hypothesis of recombination mechanism is confirmed by observation of the response of line intensities to pulsed electron heating. The partial coefficients of dissociative recombination into 2p ⁵5s states are estimated.     

Tensor polarizabilities of levels of the configurations 4f 13 6s6p and 4f 12 5d6s 2 in thulium I

The level-crossing technique with parallel electric and magnetic fields was used to measure the tensor polarizabilities of six levels of the configuration 4f ¹³ 6s6p + 4f ¹² 5d6s ² in the Tm I-spectrum. Using intermediate coupling wave functions given by Camus and the experimental values of the tensor polarizabilities, the radial integrals for electric dipole transitions from levels of the configuration 4f ¹³6s6p + 4f ¹²5d6s ² to levels of the configuration 4f ¹³ 5d6s + 4f ¹² 6s ²6p have been determined. The results areI(4f ¹³6s6p,4f ¹³5d6s)=1.98(45)ea ₀ andI(4f ¹²5d6s ²,4f ¹²6s ²6p) = 0.88(25)ea ₀. A comparison between the experimental and the calculated values of the tensor polarizabilities shows an excellent agreement, provided that these radial integrals and the radial integrals for the electric dipole transitions to the ground state configuration 4f ¹³6s ² as determined by Wallenstein from lifetime measurements are used in the calculation, instead of radial integrals computed by Camus with Hartree-Fock wave functions.     

Many-electron character of Rydberg series converging to the ionization thresholds of the 4<Emphasis Type="Italic">p</Emphasis><Superscript>4</Superscript>5<Emphasis Type="Italic">s</Emphasis> states of KrII

The photoionization cross sections of the 4p shell and the 4s main level and 4p ⁴(³ P) 5s ⁴ P _{5/2, 3/2} satellite subvalence levels of KrII have been calculated in the 4s-near-threshold range of excitation energies from 28.48 to 28.70 eV. The calculation takes into account the core relaxation by the methods of the theory of non-orthogonal orbitals, the interaction between resonant states through autoionization channels by solving the complex secular equation, and the interaction between the channels of the continuous spectrum in all orders of the perturbation theory by the K-matrix method. Good quantitative agreement between the energy-integrated theoretical and experimental photoionization cross sections for the satellite levels has been obtained for the first time. It is shown that only simultaneous consideration of the above-mentioned effects leads to such agreement. The resonant structure of the photoionization cross sections in this excitation energy range is related to the autoionization decay of the 4p ⁴5s(⁴ P _1/2)np and 4p ⁴5s(² P _3/2)np Rydberg series. The specificity of this process is that both series manifest themselves not independently but owing to their strong electrostatic interaction with the prominent 4p ⁴(¹ D)5s ² D _5/2 6p _3/2 resonance, which lies in this excitation energy range.     

The role of the configuration interaction in excitation of the Cd(II) principal series at electron-atom collisions

The excitation functions of Cd(II) spectral lines, namely, the lines of the 4d ¹⁰5s ² S _1/2?4d ¹⁰ np ² P ₃ ^2/0 (n≤10) principal series and the line corresponding to a transition from the Beitler level 4d ⁹(5s5p ¹ P ⁰)² P ₃ ^2/0 , are analyzed under the conditions of electron-cadmium atom collisions in the electron energy range from excitation thresholds to 400 eV. It is found that the excitation functions of the spectral lines attributed to transitions from the Beitler level are similar to those of the principal series lines corresponding to transitions from the 4d ¹⁰ np ² P ₃ ^2/0 (n=9, 10) levels nearest to the Beitler level. This similarity is explained by the significant admixing of the Beitler level to the initial levels of the principal series lines. It is shown that the admixing substantially affects the excitation functions of this series for the states more distant from the Beitler level (up to n=6).     

Contribution of hexadecapole alignment to the polarization of quadrupole emission under laser excitation conditions

The linear polarization of quadrupole emission by the J=2-J ₀=0 transition under conditions of laser excitation in a gas medium is studied. Cases of excitation through dipole and quadrupole absorption of monochromatic laser radiation are considered. Taking into account the anisotropy of collisional relaxation, the contributions of polarization moments of the second and fourth ranks, i.e., those with usual and hexadecapole alignments, to the signal of linear polarization of quadrupole emission are calculated. The dependence of this signal on the laser frequency, the density of the gas medium, and the angles determining the orientation of the system of axes of observation of light polarization relative to a laser ray is studied. The numerical calculations of contributions of usual and hexadecapole alignment to the signal of linear polarization are made for the magnetic quadrupole transition J=2-J ₀=0 between the states 2p ⁵(² P ₁ ^2/0 )3p′[3/2]₂ and 2p ⁵(² P ₁ ^2/0 )3s 3s′[1/2]⁰ of neon atoms in the xenon atmosphere.     

Transition probabilities of some lines of Ne(I)

Relative transition probabilities for twenty-four spectral lines belonging to 3p-3d transition array of neutral neon have been determined by means of emission line-intensity measurements. The lifetime of the 3d(3/2)₂ level has been measured by the delayed coincidence method obtaining a value of 20.5±2.0 ns. With this lifetime value and taking into account the 3887.1 Å forbidden line, the transition probabilities of the lines with origin in the 3d(3/2)₂ level were put on an absolute scale. The experimental values of the present work are compared with theoretical calculations obtained by use of the Coulomb approximation and intermediate coupling scheme.     

Low pressure broadening and shift of the 2p 53p-2p 56s neon spectral lines

Natural radiative lifetimes in the perturbed 6s n s ¹ D ₂ (n=12?30) sequence of barium have been measured using the PUMOLS (PUlse-MOdulated Laser Spectroscopy) method, which incorporates pulse-modulation of a CW dye-laser beam and delayed coincidence techniques. Principal perturbers are the 5d 7d ³ F ₂ and¹ D ₂ states. Lifetimes were also measured for these shortlived valence states, which through configuration mixing cause drastic decreases in lifetime values in the region of perturbation of the 6s n d ¹ D ₂ sequence. Two-step laser excitation from the ground 6s ^{2 1} S ₀ state via the 6s 6p ¹ P ₁ state was employed. Special care was taken to determine the influence of black-body radiation transitions on the measured lifetimes.     

Hyperfine structure induced isotopic effects in krypton resonance ionization mass spectrometry

A time-of-flight mass spectrometer combined with a pulsed laser system has been used for determination of krypton isotope ratios of air samples containing 10⁶-10⁷ krypton atoms. A three-color, doubly resonant ionization scheme employing a 116.48 nm transition from the ground into the first 4s²4p⁵(²P°_1/2)5s J = 1 excitation level has been applied. The magnitude of a hyperfine splitting of this level has been estimated for ⁸¹Kr, ⁸³Kr and ⁸⁵Kr isotopes. Hyperfine structure induced isotopic effects have been investigated under different saturation conditions and found to be negligible when the first and the second transitions are strongly saturated.     

Experimentally determined transition probabilities of the systems 6p2→6p6d, 6p7s, 6p8s of neutral lead

Branching ratio measurements have been performed for all of the observed transitions from eight levels in neutral lead (6p²→6p6d, 6p²→ 6p7s, 6p²→6p8s) excited in a hollow cathode discharge in the 200–730 nm spectral range. From the relative emission intensity data, a set of absolute transition probabilities is derived for 28 lines, including lines for which transition probabilities have not been previously published. The absolute scales are obtained by averaging the measured lifetimes of the ³P⁰_1,2, ¹P_1⁰(6p7s), ³F^0_2,3, ³D^0_1,2(6p6d) levels.     

Room temperature minority carrier lifetime and efficiency of p-type GaAs1−xPx

Using sine wave modulated laser excitation, the optical phase shift of the luminescence of vapor grown Zn doped GaAs_1?xP_x layers was measured. From such measurements the minority carrier lifetime can be derived. This lifetime was measured as a function of doping level for crystals with a composition sufficiently remote from the cross-over composition (0.30 < x < 0.35 to ascertain that only a small fraction of the minority carriers is in the indirect minima. In addition, luminescence efficiency measurements were made using cathode ray excitation. From the lifetime and efficiency results it is concluded that for p < 2 × 10¹⁹cm^-3 the lifetime, being between 1 and 3 ns, is dominated by nonradiative transitions. For the radiative transitions a rate constant of 4.5 × 10^-11cm³s^-1 was determined. This value compares reasonably well with values known for GaAs, about 7 × 10^-11cm³s^-1. The efficiency of a few strongly doped samples (p > 10¹⁹cm^-3) may be depressed by self-absorption of the luminescence. In addition, a few samples with a higher phosphorus content, up to x = 0.45, were measured. Their lifetimes being mainly determined by indirect transitions are also in the low nanosecond range. This stands in contrast with the longer lifetimes (up to 150 ns at p < 10¹⁷ cm^-3) of indirect bandgap material (x ≈ 0.8).     

A 480 ms isomeric 29/2−-state of the(p_{1/2}^{ - 2} )_{0^ + } f_{5/2}^{ - 1} (i_{13/2}^{ - 2} )_{12^ + } configuration in203Pb

A new, 480 ms, 29/2^? isomeric level has been found in²⁰³Pb at an excitation energy of 2950.1 keV by bombarding²⁰⁴Hg with α-particles in the energy range 45–55 MeV using the Stockholm 225-cm cyclotron. This 29/2^? state is suggested to be mainly due to the configuration (p ₁ ^2/?2 f ₅ ^2/?1 i ₁₃ ^2/?2 )₁₂. The 29/2^? state decays predominantly by a 153.4 keV M2 transition to a 23/2^? level and by a 1027.5 keV M4 transition to a 21/2⁺ level, followed by two E2 transitions of energies 258.6 keV and 838.7 keV, respectively, to the previously known 13/2⁺, 6.4 s isomeric level. The decay scheme of the 29/2^? isomeric state is based on experimental information obtained from total and delayedγ-ray intensities,γγ-coincidences, excitation functions, lifetime and delayed conversion electron measurements. The presence of the 29/2^? level confirms an essential and expected feature of the shell model for five neutron holes added to the²⁰⁸Pb-core.     

The probability of prompt and delayed fission of muonic237Np

Fission fragments from the reaction²³⁷Np(μ ^?,γ,f) have been measured in coincidence with muonic X-rays. The efficiency of the fission fragment detector is determined from (μ ^?,γ,f)-data of the same experiment. The total fission probability perμ-stopP _t has been measured as well as the fission probabilities P_f of the non-radiative muonic (3d→1s)- and (2p→1s)-transitions; the latter has been divided into two parts leading to different mean excitation energiesE:P _t =(54±17)%,P _f (3d→1s)=(41±21)%,P _f (2p→1s,E=6.218 MeV)=(61±19)%, andP _f (2p→1s,E=6.525 MeV)=(57±18)%. The influence of the muon on the fission barrier is discussed. The fission probability after muon capture is compared with a calculated value using a distribution of nuclear excitation energies following muon capture and the fission probability as measured in a²³⁸U(³He,αf)-reaction.     

Experimental transition probabilities of some Xe(I) lines

Using the light absorption technique in a ¹³²Xe afterglow plasma, we have measured the relative transition probabilities for several xenon lines which have the metastable 6s[$\text{3}\text{2}$]₂ or the resonant 6s[$\text{3}\text{2}$]₁ states as their lowest transition level. Because the transition probabilities of the 8819 Å (6p[$\text{5}\text{2}$]₃ ? 6s[$\text{3}\text{2}$]²) and 8280 Å (6p[$\text{1}\text{2}$]₀ ? 6s[$\text{3}\text{2}$]₁) lines are relatively well known, we have chosen these as reference lines and have thus been able to determine the absolute values of the transition probabilities for 19 xenon lines corresponding to transitions from 6p, 6p′, 7p, 8p, 9p, 4f and 5f to 6s[$\text{3}\text{2}$]₂, and for four lines corresponding to the transitions 6p?6s[$\text{3}\text{2}$]₁.