Excited Even-parity Research Articles

Three-Photon Resonance Ionization Spectroscopy of Excited Even-Parity States of the Samarium Atom

Excited even-parity states of the samarium atom in the energy interval 32620–34092 cm−1 have been studied by using single-color three-photon resonance ionization spectroscopy. The energies and total angular momenta of 72 states were determined. Nine new levels were revealed.

New spectroscopic data on high-lying excited even-parity levels of atomic neodymium

The two-color three-photon photoionization technique was used to obtain information on high-lying excited even-parity levels of atomic neodymium in the 32,100–35,300 cm−1 energy region. 417 even-parity levels, most of which were reported for the first time, were revealed. Out of these, 172 levels were assigned unique J values based on the J-momentum selection rule. The absolute accuracy of these levels was estimated to be better than ±0.2 cm−1.

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)

Investigation of highly excited states of samarium

Highly excited even-parity states of the samarium atom in the range between 34104 and 39155 cm−1 have been studied by the method of one-color three-photon resonance ionization spectroscopy. The energies and total angular momenta of 342 states have been determined. Seven new even-parity states of samarium have been discovered.

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.

Radiative lifetime measurements of highly excited even-parity levels of Eu i

Natural radiative lifetime measurements have been performed for 186 even-parity highly excited levels of neutral europium in the energy range from 27852.90 to 45106.83 cm -1 using a time-resolved laser-induced fluorescence technique in a laser-produced plasma. This work is the largest-scale laboratory study to date of Eu I radiative lifetimes using modern methods. The lifetime values measured in this paper are in the range from 17.0 to 3569 ns. Comparison with previous data reveals a good level of agreement. Unique J-values of the 43438.19- and 43637.11-cm -1 levels have been assigned. The present work will be useful for extending the set of oscillator strengths available for Eu I.

Experimental study of highly excited even-parity bound states of the Sm atom

In this work, a three-step autoionization detection method and direct photoionization detection method are employed to measure the highly excited even-parity states of the Sm atom in the energy region between 36360 cm−1 and 40800 cm−1. Comparisons between the results from the two detection techniques enable us to discriminate the Rydberg states from the valence states in the same energy region with the information of level energies, possible J values and their relative intensities. Furthermore, in the experiment two different excitation schemes are designed to obtain the spectra of highly excited even-parity states of the Sm atom. With a detailed analysis of the experimental data, this work not only confirms the results about many spectral data from the literature with different excitation schemes, but also reports new spectral data on 29 Rydberg states and 23 valence states.

Two-step laser excitation of the highly excited even-parity states of atomic mercury

We report term energies and quantum defects of highly excited even-parity states of mercury in the 83 876–84 140 cm-1 energy range, employing a two-step laser excitation scheme via the $6s^2 ~^1$ S0↦6s6p3P1 inter-combination transition. Two dye lasers, pumped by a common Nd:YAG laser, were frequency doubled by BBO crystals and used to record the spectra in conjunction with a thermionic diode ion detector. Our new observations include the much extended $6snd ~^3$ D2 (22 ≤n ≤52) series and a few members of the $6sns ~^3$ S1 (24 ≤n ≤30) Rydberg series. Members of the $6snd ~^3$ D2 Rydberg series with such a high n value are reported for the first time. The relative intensities of the $msnd ~^3$ D2 and $msns ~^3$ S1 transitions (m = 4, 5 and 6) of group II-B elements excited from the $msmp ~^3$ P1 inter-combination states are also discussed.

Even- and odd-parity charmed meson masses in heavy hadron chiral perturbation theory

We derive mass formulae for the ground state, J^P = 0^- and 1^-, and first excited even-parity, J^P = 0^+ and 1^+, charmed mesons including one loop chiral corrections and O(1/m_c) counterterms in heavy hadron chiral perturbation theory. We show that including these counterterms is critical for fitting the current data. We find that certain parameter relations in the parity doubling model are not renormalized at one loop, providing a natural explanation for the equality of the hyperfine splittings of ground state and excited doublets.

Two-step laser spectroscopy of the highly excited even-parity levels of cadmium

We report experimental data on the highly excited even-parity states of cadmium in the energy range 70 960–72 500 cm−1 employing a two-step laser excitation scheme via the 5s5p 3P1 inter-combination line. Two frequency doubled dye lasers simultaneously pumped by a common Nd:YAG laser were used to record the spectra using a thermionic diode ion detector. New observations include much-extended 5snd 3D2 (11 ⩽ n ⩽ 52) and 5sns 3S1 (12 ⩽ n ⩽ 38) Rydberg series, whereas the 5snd 1D2 series have been detected from n = 11 to 26. A two-parameter fit to the transition energy of 5snd 3D2 series yields the binding energy of the 5s5p 3P1 level as 41 883.97 ± 0.05 cm−1 and, consequently, the first ionization potential of cadmium is determined as 72 540.06 ± 0.13 cm−1, in good agreement with that reported by Brown et al (1975 J. Opt. Soc. Am. 65 1404).

Energy exchange dynamics of the discrete nonlinear Schrödinger equation lattice and intrinsic formation of strongly localized states

We study the dynamics of excitation energy transfer along a lattice chain modeled by the discrete nonlinear Schr\odinger (DNLS) equation. We prove that a segment carrying resonant motion can be decoupled from the remainder of the chain supporting quasiperiodic dynamics. The resonant segment from the extended chain is taken to be a four-site element, viz., a tetramer. First, we focus interest on the energy exchange dynamics along the tetramer viewed as two weakly coupled DNLS dimers. Hamiltonian methods are used to investigate the phase-space dynamics. We pay special attention to the role of the diffusion of the action variables inside resonance layers for the energy migration. When distributing the energy initially equally between the two dimers one observes a directed irreversible flow of energy from one dimer into the other assisted by action diffusion. Eventually on one dimer a stable self-trapped excitation of large amplitude forms at a single site while the other dimer exhibits equal energy partition over its two sites. Finally, we study the formation of localized structure on an extended DNLS lattice chain. In particular we explore the stability of the so-called even-parity and odd-parity localized modes, respectively, and explain their different stability properties by means of phase-space dynamics. The global instability of the even-parity mode is shown. For the excited even-parity mode a symmetry-breaking perturbation of the pattern leads to an intrinsic collapse of the even-parity mode to the odd-parity one. The latter remains stable with respect to symmetry-breaking perturbations. In this way we demonstrate that the favored stable localized states for the DNLS lattice chain correspond to one-site localized excitations.

Near-threshold photoionization spectrum of aligned Ca 4s5p 1P1.

The relative cross section for photoionization from the 4s5p $^{1}$${\mathit{P}}_{1}$ excited level of neutral calcium has been measured using pulsed laser excitation and ionization of Ca atoms in an atomic beam. Photoelectrons are counted as a function of ionizing photon energy and polarization. Measurements cover the energy range from 51 300 to 51 700 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ above the Ca $^{1}$${\mathit{S}}_{0}$ ground state at a resolution of approximately 0.15 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. The shapes and relative peak heights of resonances corresponding to the previously identified $^{3}$${\mathit{S}}_{1}$ and $^{3}$${\mathit{D}}_{1,2}$ autoionizing levels from the 3d4d configuration have been determined. A new, extremely strong resonance is also evident at 51 467 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$, and it has been tentatively identified with the 3d4d $^{1}$${\mathit{P}}_{1}$ level. This is an experimental identification of a doubly excited even-parity singlet level in calcium.

Experimental and theoretical study of the hyperfine structure in the 4f75d6s6p configuration of Gd I.

A parametric hyperfine-structure (hfs) analysis of 24 excited even-parity levels of the 4${\mathit{f}}^{7}$5d6s6p configuration in Gd i was performed. The interpretation has been carried out based on a refined multiconfigurational fine-structure (fs) calculation taking altogether 177 assignments into account. The set of fs parameters as well as the leading eigenvector percentages of levels relevant for this paper are given. SL-limit effective-operator expressions are presented for the magnetic-dipole and electric-quadrupole hfs of arbitrary states built from four open electron shells. The following single-electron hfs parameters ${\mathit{a}}_{6\mathit{s}}^{10}$ and ${\mathit{b}}_{6\mathit{p}}^{02}$ were deduced for $^{155}\mathrm{Gd}$, ${\mathit{a}}_{6\mathit{s}}^{10}$=-1270(22) MHz, ${\mathit{b}}_{6\mathit{p}}^{02}$=1507(26) MHz and for $^{157}\mathrm{Gd}$, ${\mathit{a}}_{6\mathit{s}}^{10}$=-1668(28) MHz, ${\mathit{b}}_{6\mathit{p}}^{02}$=1603(29) MHz. For the odd-parity level 4${\mathit{f}}^{7}$5d6${\mathit{s}}^{2}$ $^{7}$${\mathit{D}}_{4}$ the magnetic-dipole A and electric-quadrupole B hfs constants were found to be $^{155}$A=-11.3(2.1) MHz, $^{155}$B=54(9) MHz, $^{157}$A=-14.8(2.7) MHz, and $^{157}$B=58(10) MHz. The validity of all single-electron hfs parameters was checked using general trends of the corresponding 〈${\mathit{r}}^{\mathrm{\ensuremath{-}}3}$${\mathrm{〉}}_{\mathit{n}\mathit{l}\mathit{s}}^{\mathit{k}}$${\mathit{k}}_{\mathit{l}}$ values known for the series of the lanthanides. Finally, the evaluation of the electric nuclear quadrupole moment is discussed.

Hyperfine structure of the 4f75d26s 11F term of 155,157Gd I by laser-rf double resonance.

The atomic-beam laser-rf double-resonance method has been used to measure the hyperfine structure (hfs) of the J=2--8 levels of the $^{11}\mathrm{F}$ term of 4${f}^{7}$5${d}^{2}$6s in $^{155}$,157Gd. Results are also reported for the J=2,5 levels of the $^{7}\mathrm{D}$ term of 4${f}^{7}$5d6${s}^{2}$. Less precise hfs results are given for ten highly excited even-parity levels, and isotope shifts are given for 16 optical lines. L-S limit effective-operator expressions are given for the hfs A and B values of arbitrary states built from three open electron shells. When specialized to the $^{11}\mathrm{F}$ term in Gd i, these expressions reveal a marked perturbation between the J=5 levels of 4${f}^{7}$5${d}^{2}$6s $^{11}F$ and 4${f}^{7}$5d6${s}^{2}$ $^{7}D$. The perturbation can also be detected from the fine-structure intervals.

Nonlinear level crossing spectroscopy of highly excited levels in yttrium using stepwise laser excitation

A technique based on the detection of nonlinear level-crossing resonances in finite magnetic fields has been extended to the study of high-lying electronic levels excited by stepwise excitation with two cw dye lasers. The method has been applied to the determination of |A/g J | values for four highly excited even-parity levels and two odd-parity levels in yttrium I. Using recently determined values of the magnetic hyperfine interaction constantA, Landeg J -factors have been deduced for these levels with an accuracy of about 1%. The results show significant differences from previous determinations.

Rotational bands in the baryon spectrum

As suggested by the bag model, we assume that the ground states of the nucleon and the $\ensuremath{\Delta}$ are nearly spherical, but the excited even-parity states are quite deformed. This deformation is responsible for the observed low-lying excitations $N(1440){\frac{1}{2}}^{+}$ and $\ensuremath{\Delta}(1600){\frac{3}{2}}^{+}$, on which rotational bands are built.

Emission Spectra of Core Excited Even-ParityP2States of Neutral Lithium

Doubly excited even-parity lsnpmp /sup 2/P states of neutral Li are metastable against autoionization and have large radiative yields. An emission spectrum from 160 A to 250 A of a high-power-microwave--heated Li plasma is reported. The spectrum, which differs substantially from that obtained in absorption, exhibits several new series as well as the phenomena of radiative autoionization.