High-lying Even-parity Research Articles

Investigation of high-lying even-parity levels of atomic samarium with multi-color photoionization technique: Energies and radiative lifetimes

We have investigated high-lying even-parity energy levels of atomic samarium in the energy region 32,156.3–32,886.4 cm−1 using two-color three-step photoionization technique. The experiments have been carried out in an atomic beam coupled to a linear time of flight mass spectrometer. The analysis of the photoionization spectra has resulted in the identification of twenty-five high-lying even-parity energy levels of atomic samarium. These include the confirmation of fifteen energy levels reported earlier while the remaining ten energy levels are new. The observed relative photoionization signal intensities of the corresponding transitions are also reported. The possible total angular momenta of the newly discovered energy levels have been assigned by the total angular momentum selection rules. Further, the radiative lifetimes of twenty high-lying even-parity energy levels of atomic samarium were measured for the first time by delayed three-color three-photon resonance ionization spectroscopy via a pump-probe method.

Lifetime measurements using two-step laser excitation for high-lying even-parity levels and improved theoretical oscillator strengths in Y ii

We report new time-resolved laser-induced fluorescence lifetime measurements for 22 highly excited even-parity levels in singly ionized yttrium (Y II). To populate these levels belonging to the configurations 4d6s, 5s6s 4d5d, 5p2, 4d7s and 4d6d, a two-step laser excitation technique was used. Our previous pseudo-relativistic Hartree-Fock model (Biemont et al. 2011) was improved by extending the configuration interaction up to n = 10 to reproduce the new experimental lifetimes. A set of semi-empirical oscillator strengths extended to transitions falling in the spectral range λλ194-3995 nm, depopulating these 22 even-parity levels in Y II, is presented and compared to the values found in the Kurucz's data base (Kurucz 2011). (Less)

Investigations of high-lying even-parity energy levels of atomic samarium using simultaneous observation of two-color laser-induced fluorescence and photoionization signals

Laser-induced photoionization and fluorescence signals were simultaneously observed in atomic samarium using two Nd:YAG-pumped dye lasers. Two-color, three-photon photoionization and two-color fluorescence signals were recorded simultaneously under similar experimental conditions and their dependence as a function of the second-step laser power was studied to understand the behavior of these signals. The laser-induced fluorescence and photoionization techniques have been used simultaneously for the first time to understand the behavior of these signals so that these techniques can be used efficiently in complementary manner to investigate the high-lying energy levels. The even-parity energy levels of atomic samarium in the energy region 36 510–36 875 cm-1 have been investigated based on these experiments. Total 21 high-lying even-parity energy levels have been identified and the two energy levels amongst them are reported as new energy levels after comparing our results with those reported in the literature.

Radiative lifetimes of highly excited even-parity levels in Gd i and Gd ii

Radiative lifetimes of 94 high-lying even-parity levels from 29 717.231 to 41 692.155 cm−1 of Gd i and 10 high-lying even-parity levels from 38 057.954 to 49 291.082 cm−1 of Gd ii, have been measured using time-resolved laser-induced fluorescence method. The lifetime values range from 7.1 to 220 ns for Gd i and from 5.2 to 47.4 ns for Gd ii. Most results reported here lie within the uncertainty of ±5 per cent. Free neutral and singly ionized gadolinium atoms were generated by laser ablation. The second harmonic of different dye lasers was employed as the tunable UV exciting source (242–337 nm) to excite the investigated levels. A good agreement between our results and the previous ones was achieved.

Measurement of total angular momentum values of high-lying even-parity atomic states of samarium by spectrally resolved laser-induced fluorescence technique

Spectrally resolved laser-induced fluorescence technique was used to uniquely assign total angular momentum (J) values to high-lying even-parity energy levels of atomic samarium. Unique J value assignment was done for seven energy levels in the energy region 34,800–36,200 cm−1, recently observed and reported in the literature.

Electronic bridge process inTh229+

We have studied the effect of atomic electrons on the nuclear transition from the isomeric {229m}Th state to the ground {229g}Th state in {229}Th+ due to the electronic bridge process. The exact value of the nuclear transition frequency is unknown so far; therefore, we have developed a formalism that can be used for any nuclear transition frequency. We have calculated positions of several high-lying even-parity states which are not presented in experimental atomic spectra databases. We have found their energy levels and g factors.

Investigations of new high-lying even-parity energy levels of the samarium atom below its first ionization limit

Systematic mapping of high-lying even-parity levels (low-lying configurations) of the samarium atom below the first ionization potential was carried out with a two-step photoexcitation and photoionization method. Five hundred seventy-one new energy levels were discovered in the region 34 850–45 300 cm-1, and an unambiguous assignment of angular momenta was given to most of the energy levels in accordance with the electric dipole selection rules.

Hyperfine structure and isotope shifts of high-lying levels of Zr I investigated by laser-induced fluorescence spectroscopy

High-resolution laser-induced fluorescence spectroscopy has been applied to investigate the hyperfine structure constants and isotope shifts of high-lying even-parity levels of zirconium in the energy range 34 000–37 000 cm-1. By analysis of the measured spectra, the hyperfine-structure constants of seven levels and isotope shifts of eight transitions are determined.

Hyperfine structure studies of 93Nb by three-step resonance ionization spectroscopy

The hyperfine structure of 93Nb is studied by three-step resonance ionization spectroscopy with electric field ionization. The atomic beam is produced by thermal evaporation. The hyperfine splitting of eight J = 12 states, namely the ground state, five odd-parity states belonging to the configurations 4d 45p and 4d 35s5p, and two high-lying even-parity states belonging to the configurations 4d 46s and 4d 35s6s, is reported. The convergence limit of a Rydberg series obtained by exciting one of the even-parity states is determined. The possibility of isomer ( 93mNb) selective laser excitation and ionization of niobium is discussed in relation to fast-neutron fluence monitoring by an activation reaction of niobium.

Selective isotope determination of lanthanum by diode-laser-initiated resonance-ionization mass spectrometry

A diode-laser step has been incorporated into a resonance-ionization mass spectrometry optical excitation process to enhance the isotopic selectivity of the technique. Lanthanum isotope ratio enhancements as high as 103 were achieved by use of a single-frequency cw diode laser tuned to excite the first step of a three-step excitation–ionization optical process; the subsequent steps were excited by use of a pulsed dye laser. Applying the same optical technique, we measured atomic hyperfine constants for the high-lying even-parity 4D5/2 state of lanthanum at 30 354 cm−1. The general utility of this spectral approach is discussed.

Studies of high-lying even-parity levels of Sm i: energies and isotope shifts

Absolute energies and isotope shifts of high-lying even-parity levels of Sm i have been measured by resonantly enhanced Doppler-free two-photon spectroscopy in a hollow-cathode discharge tube. The two-photon transitions in the experiment originate from the levels at 1489.55 cm−1 (7F3) and 2273.09 cm−1 (7F4) of the 4f66s2 configuration and terminate at the high-lying levels ranging from 35 779.26 to 37 054.07 cm−1. Through detection of the laser-induced fluorescence with a monochromator, the J values of these high-lying levels have been partially determined.

Hyperfine-structure studies of high-lying even-parity levels of ^139La i by resonantly enhanced Doppler-free two-photon spectroscopy

The technique of employing resonantly enhanced Doppler-free two-photon excitation from either the ground state or a low-lying metastable state for precisely measuring the hyperfine structure of the atomic high-lying levels has been used, for the first time to our knowledge, to study 139La i. By detecting the laser-induced fluorescence produced in a hollow-cathode discharge tube, one can measure a set of spectra for each two-photon transition line. The spectra are analyzed in detail and fitted to yield hyperfine structure constants. The A values of eight high-lying even-parity levels of 139La i are then determined.

Photoionization spectroscopy of even-parity levels of Fe i

Multistep laser photoionization spectroscopy has been used to study high-lying even-parity levels in the Fe i spectrum. The first laser excites atoms in an iron atomic beam from a ground-state level to an intermediate odd-parity level, y5DJ. A second laser resonantly two-photon ionizes these excited atoms through even-parity levels in the energy range 54 500–58 000 cm−1. Thirty-four new even-parity energy levels are reported in this range, and they are assigned to Fe i configurations 3d64s(6D)6s, 3d64s(6D)5d, 3d64s(4D)4d, and 3d7(4F)6s.

Radiative lifetimes of even- and odd-parity levels in Sc i and Sc ii

Time-resolved laser-induced fluorescence on atomic and ionic beams is used to measure radiative lifetimes for 77 odd- and even-parity levels of Sc i and Sc ii. Time-of-flight selection of slow scandium atoms is demonstrated to minimize a systematic error in long lifetimes, an error that arises because atoms escape from the observing region before radiating. High-lying even-parity levels in Sc i and Sc ii are excited by using two-step laser excitation.

Experimental study of high-lying even-parity states in barium by two-photon absorption spectroscopy

Highly excited Rydberg and autoionized levels were investigated by using selective absorption spectroscopy and the space charge amplification method for detecting ions. The one-photon absorption spectrum from the ground state 6s2 1S0 has been recorded by scanning the emitted continuum from a mercury lamp with a 2 m Czerny-Turner monochromator. With the allowed resolution of 0.1 AA, 6snp 1P10 Rydberg states were observed up to n=45. Furthermore, two-photon absorption spectroscopy was performed using a 0.150 cm-1 tunable dye laser radiation over the range 4200-5600 AA. Even-parity states J=0 and J=2 belonging to the series 6sns and 6snd up to n=46 and n=77, respectively, and new autoionized levels belonging to 5dns and 5dnd configurations were observed.