Band Head Research Articles

Strontium isotope analysis using laser-induced breakdown spectroscopy and molecular laser-induced fluorescence at various atmospheric conditions

The strontium isotope was analyzed by the combination system of laser-induced breakdown spectroscopy (LIBS) and molecular laser-induced fluorescence (MLIF). The fluorescence from A1Σ+ → X1Σ+ transition of strontium monoxide was observed by the selective excitation of individual vibrational band heads, and its spectral feature was investigated under atmospheric conditions being adjusted. In the fluorescence spectra of LIBS-MLIF, the signal intensity was improved about 10 times higher than the single LIBS, and each isotopologue could be clearly identified with an isotope shift of about 0.1 nm. By comparing these fluorescence signals, the isotope effect on molecular radicals in laser-induced plasma was investigated. The spatial distribution and the formation kinetics of isotopologues could be influenced by the isotopic effect, which exhibits a unique fluorescence behavior. It is noteworthy that the degree of isotopic effect on radicals could be modulated by controlling the atmosphere. Under the condition of reduced isotope effect, the strontium isotopic abundance could be accurately estimated within the error of 5% by the fluorescence ratio. The present work not only demonstrated the feasibility of LIBS-MLIF for the detection of strontium isotopes, but also provides novel insight into the molecular formation and isotopic effects in laser-induced plasma.

Line mixing in the oxygen B band head.

We present the results of direct measurements of the line mixing parameters for two pairs of overlapping transitions at the band head of the oxygen B band. Measurements were performed with the frequency-stabilized cavity ring-down spectrometer assisted by an optical frequency comb. The recorded spectra were analyzed with line profiles comprising speed dependence, Dicke narrowing, and line mixing. Incorporation of the line mixing into the model eliminated previous discrepancies for pressure shift and their speed dependence coefficients. First-order line mixing was determined directly from the line shape fitting at relatively low pressure (0.04 atm) together with other line shape parameters and compared with that calculated by Sung et al. [J. Quant. Spectrosc. Radiat. Transfer 235, 232-243 (2019)].

Optimal focal curve of spherical mirrors used in a high resolution UV-A spectrograph

The present study concerns the determination of the optimal focal curve of the reflected beam from a spherical mirror. This study has been used in a stigmatic high resolution UV-A spectrograph operating in UV-A region. As a light source we have used a low pressure air discharged lamp while the light detector was a cooled CCD camera with a resolution of 1600×1200 pixels. Locating it on the optimal position along the useful spectral range allows us to exploit the full resolution provided by the spectrograph. An analytical expression of the focal curve has been derived as a function of the main geometrical parameters of the spectrograph and the focusing spherical mirror. A set of experimental validation tests have been performed recording several band heads and the associated molecular rotational lines of nitrogen provided by the lamp. The obtained result has been used in high resolution spectroscopy relevant to air fluorescence yield determination in Ultra High Energy Cosmic Ray research.

Gaia-ESO Survey: Detailed elemental abundances in red giants of the peculiar globular cluster NGC 1851

Context. NGC 1851 is one of several globular clusters for which multiple stellar populations of the subgiant branch have been clearly identified and a difference in metallicity detected. A crucial piece of information on the formation history of this cluster can be provided by the sum of A(C+N+O) abundances. However, these values have lacked a general consensus thus far. The separation of the subgiant branch can be based on age and/or A(C+N+O) abundance differences. Aims. Our main aim was to determine carbon, nitrogen, and oxygen abundances for evolved giants in the globular cluster NGC 1851 in order to check whether or not the double populations of stars are coeval. Methods. High-resolution spectra, observed with the FLAMES-UVES spectrograph on the ESO VLT telescope, were analysed using a differential model atmosphere method. Abundances of carbon were derived using spectral synthesis of the C2 band heads at 5135 and 5635.5 Å. The wavelength interval 6470−6490 Å, with CN features, was analysed to determine nitrogen abundances. Oxygen abundances were determined from the [O I] line at 6300 Å. Abundances of other chemical elements were determined from equivalent widths or spectral syntheses of unblended spectral lines. Results. We provide abundances of up to 29 chemical elements for a sample of 45 giants in NGC 1851. The investigated stars can be separated into two populations with a difference of 0.07 dex in the mean metallicity, 0.3 dex in the mean C/N, and 0.35 dex in the mean s-process dominated element-to-iron abundance ratios [s/Fe]. No significant difference was determined in the mean values of A(C+N+O) as well as in abundance to iron ratios of carbon, α- and iron-peak-elements, and of europium. Conclusions. As the averaged A(C+N+O) values between the two populations do not differ, additional evidence is given that NGC 1851 is composed of two clusters, the metal-rich cluster being by about 0.6 Gyr older than the metal-poor one. A global overview of NGC 1851 properties and the detailed abundances of chemical elements favour its formation in a dwarf spheroidal galaxy that was accreted by the Milky Way.

Chiral vibrations and collective bands in Mo104,106

High spin states of the neutron-rich $^{104}\mathrm{Mo}$ nucleus have been reinvestigated by analyzing the $\ensuremath{\gamma}$ rays in the spontaneous fission of $^{252}\mathrm{Cf}$ with Gammasphere. Both $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ and $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidence data were analyzed. A new $\mathrm{\ensuremath{\Delta}}I=1$ band has been discovered with a tentative ${5}^{\ensuremath{-}}$ band head, and is proposed to form a class of chiral vibrational doublets with another ${4}^{\ensuremath{-}}$ band previously found. Angular correlation measurements have been performed to determine the spins and parities. A new ${3}^{\ensuremath{-}}$ level has been added to one of the chiral doublet bands in $^{106}\mathrm{Mo}$. The origin of the chiral doublet bands in $^{104,106}\mathrm{Mo}$ is interpreted as a neutron ${h}_{11/2}$ particle and mixed ${d}_{5/2}, {g}_{7/2}$ hole coupled to the short and long axis, respectively. Triaxial projected shell model calculations have been performed for the chiral doublet bands in $^{104,106}\mathrm{Mo}$. The results show reasonably good agreement with the experimental data.

New Infrared Spectral Indices of Luminous Cold Stars: From Early K to M Types

Abstract We present infrared spectral indices (1.0–2.3 μm) of Galactic late-type giants and red supergiants (RSGs). We used existing and new spectra obtained at resolution power R = 2000 with SpeX on the IRTF telescope. While a large CO equivalent width (EW), at 2.29 μm ([CO, 2.29] ≳ 45 Å) is a typical signature of RSGs later than spectral type M0, [ CO ] of K-type RSGs and giants are similar. In the [CO, 2.29] versus [Mg i, 1.71] diagram, RSGs of all spectral types can be distinguished from red giants because the Mg i line weakens with increasing temperature and decreasing gravity. We find several lines that vary with luminosity, but not temperature: Si i (1.59 μm), Sr (1.033 μm), Fe+Cr+Si+CN (1.16 μm), Fe+Ti (1.185 μm), Fe+Ti (1.196 μm), Ti+Ca (1.28 μm), and Mn (1.29 μm). Good markers of CN enhancement are the Fe+Si+CN line at 1.087 μm and CN line at 1.093 μm. Using these lines, at the resolution of SpeX, it is possible to separate RSGs and giants. Contaminant O-rich Mira and S-type AGBs are recognized by strong molecular features due to water vapor features, TiO band heads, and/or ZrO absorption. Among the 42 candidate RSGs that we observed, all but one were found to be late types. Twenty-one have EWs consistent with those of RSGs, 16 with those of O-rich Mira AGBs, and one with an S-type AGB. These infrared results open new, unexplored, potential for searches at low resolution of RSGs in the highly obscured innermost regions of the Milky Way.

A galaxy cluster in the innermost Zone of Avoidance, close to the radio phoenix VLSS J2217.5+5943

Context.Galaxy clusters grow via mergers with other clusters and groups. Extended regions of diffuse radio emission with a steep radio spectral index are thought to be indicators of such merger events. Extended radio sources with a significantly curved spectrum and a complex morphology have been found in several galaxy clusters. It has been proposed that these so-called radio phoenices are witnesses of cluster mergers and of the presence of active galactic nuclei prior to the merger. Shock fronts or turbulence induced by the mergers are believed to reenergize plasma emitted in the past active phase of a galaxy.Aims.The steep spectrum radio source VLSS J2217.5+5943 shows a complex filamentary morphology and a curved spectrum. Therefore, the source has previously been classified as a radio phoenix. However, no galaxy cluster associated with this radio source had confidently been detected until now because the source is located in the direction of the innermost zone of the Galactic plane atb = +2.4°, the innermost Zone of Avoidance (ZoA). The main aim of this work is to identify galaxies that are part of a cluster at the location of VLSS J2217.5+5943, determine their redshifts, and analyze their connection with the radio source. The confirmation of a cluster would corroborate the classification of the radio source as a radio phoenix and demonstrate that extended, diffuse radio sources are useful indicators of the presence of a galaxy cluster, in particular in the innermost ZoA.Methods.We analyzed archival observations in the near infrared and mid infrared (Spitzer) to select the galaxies in the immediate neighborhood of the radio source. A sample of 23 galaxies were selected as candidate cluster members. Furthermore, we carried out deep integral field spectroscopy covering 6450 to 10 500 Å with the red unit of theHobby-EberlyTelescope second generation low resolution spectrograph (LRS2-R). We also reanalyzed archival GMRT observations at 325 and 610 MHz.Results.We selected 23 galaxies within a radius of 2.5 arcmin, centered on RA = 22h17m​.5, Dec = +59° 43′ (J2000). Spectra were obtained for three of the brightest galaxies. For two galaxies we derived redshifts ofz = 0.165 andz = 0.161, based on NaD absorption and TiO band heads. Their spectra correspond to E-type galaxies. Both galaxies are spatially associated with VLSS J2217.5+5943. The spectrum of the third galaxy, which is slightly farther from the radio source, indicates a LINER spectral type atz = 0.042. It is apparently a foreground galaxy with respect to the cluster we identified.Conclusions.VLSS J2217.5+5943 is associated with a massive galaxy cluster at redshiftz = 0.163 ± .003, supporting its classification as a radio phoenix. The intrinsic properties of the radio source, computed for the cluster redshift, are in good agreement with those of other known radio phoenices. The identification of the galaxy cluster demonstrates that far-red spectroscopy with LRS2-R succeeds in determining the redshift of galaxies in the innermost ZoA. Moreover, it confirms that radio sources can be useful indicators of the presence of galaxy clusters in the ZoA.

MOLsphere and pulsations of the Galactic Center’s red supergiant GCIRS 7 from VLTI/GRAVITY

Context. GCIRS 7, the brightest star in the Galactic central parsec, formed 6 ± 2 Myr ago together with dozens of massive stars in a disk orbiting the central black-hole. It has been argued that GCIRS 7 is a pulsating body, on the basis of photometric variability. Aims. Our goal is to confirm photospheric pulsations based on interferometric size measurements to better understand how the mass loss from these massive stars enriches the local interstellar medium. Methods. We present the first medium-resolution (R = 500), K-band spectro-interferometric observations of GCIRS 7, using the GRAVITY instrument with the four auxiliary telescopes of the ESO VLTI. We looked for variations using two epochs, namely 2017 and 2019. Results. We find GCIRS 7 to be moderately resolved with a uniform-disk photospheric diameter of θUD* = 1.55 ± 0.03 mas (RUD* = 1368 ± 26 R⊙) in the K-band continuum. The narrow-band uniform-disk diameter increases above 2.3 μm, with a clear correlation with the CO band heads in the spectrum. This correlation is aptly modeled by a hot (TL = 2368 ± 37 K), geometrically thin molecular shell with a diameter of θL = 1.74 ± 0.03 mas, as measured in 2017. The shell diameter increased (θL = 1.89 ± 0.03 mas), while its temperature decreased (TL = 2140 ± 42 K) in 2019. In contrast, the photospheric diameter θUD* and the extinction up to the photosphere of GCIRS 7 (AKS = 3.18 ± 0.16) have the same value within uncertainties at the two epochs. Conclusions. In the context of previous interferometric and photo-spectrometric measurements, the GRAVITY data allow for an interpretation in terms of photospheric pulsations. The photospheric diameter measured in 2017 and 2019 is significantly larger than previously reported using the PIONIER instrument (θ* = 1.076 ± 0.093 mas in 2013 in the H band). The parameters of the photosphere and molecular shell of GCIRS 7 are comparable to those of other red supergiants that have previously been studied using interferometry. The extinction we measured here is lower than previous estimates in the direction of GCIRS 7 but typical for the central parsec region.

Novel evidence for the σ-bond linear-chain molecular structure in 14C * *Supported by the National Key research and development Program of China (2018YFA0404403), the National Natural Science Foundation of China (11875074, 11875073, 12027809, 11635015, 11961141003) and the Continuous Basic Scientific Research Project (WDJC-2019-13)

A multi-nucleon transfer and cluster decay experiment, Li( B, C + Be) , is conducted at an incident beam energy of 55 MeV. This reaction channel has a significantly large Q-value, which favors populating the high lying resonant states in C. The decay paths, from these resonances to various states of the final nucleus Be, can be selected, owing to the experimentally achieved optimal resolution of the Q-value spectrum. A number of resonant states are reconstructed from the forward emitting Be + fragments, and their major molecular structures can be detected according to the selective decay paths and relative decay widths. A state at 22.4(2) MeV validates the previously measured and theoretically predicted band head of the positive-parity -bond linear-chain molecular band. Two additional resonances at 22.9(2) and 24.2(2) MeV are identified and consistent with the predicted and members of the same molecular band, thus providing novel evidences for the existence of the exotic clustering chain structure in neutron-rich carbon isotopes. A few high energy resonances, which also indicate the presence of the -bond molecular structure, are observed; however, further studies are still required to clarify their ascription in band systematics.

A comparative study of KrF laser ablation of aluminum and alumina in oxygen ambiance

This paper is dedicated to a comparative study of aluminum and alumina plasmas, induced under the same conditions of laser fluence and oxygen gas pressure in the range of 0.02 to 5 mbar. In this comparative analysis, measurements of ablated mass versus laser fluence and optical emission spectroscopy diagnostic of the plasmas are studied. The results from ablated mass measurements reveal the existence of two regimes of ablation according to a laser fluence threshold for phase explosion mechanism. This laser fluence threshold was found different for Al and Al2O3. A difference in the amount of ablated mass/pulse is also observed and is assigned to the optical (reflectivity and absorption) and thermodynamical properties (evaporation temperature) of the targets. Below a certain laser fluence threshold, thermal and non-thermal processes are involved. Above this laser fluence threshold, the mechanism of ablation is assigned to phase explosion. For plasma diagnostic by optical emission spectroscopy, two species were followed; the neutral Al (396.15 nm) for its persistence in time and distance and the AlO (the band head emission at 484.21 nm) molecule that is probably the precursor in alumina thin films formation. The spectra revealed a disparity in the intensity emission of neutral Al and AlO molecules, which were, related to the target's properties. The origin of AlO molecules recorded in aluminum and alumina plasma under oxygen ambiance is discussed. Their translational temperature for neutral Al, molecular vibrational temperature, and free linear velocities, are also compared.

Properties of superdeformed bands in A < 100 mass region within the variable moment of inertia model

The variable moment of inertia (VMI) model has been used to study the properties of superdeformed (SD) bands in A < 100 mass region. The experimental γ-ray (E γ ) transitions energies are least square fitted to obtain the model parameters such as band head moment of inertia, (J 0), and stiffness constant, (C). The observed E γ transition energies obtained using the VMI formula are in excellent agreement with the experimental values. In the paper, we have studied the dynamic moment of inertia (J (2)) and its variation with rotational frequency (ℏ ω). We also studied the ΔI = 2 staggering phenomena in SD bands of 61Zn(SD), 62Zn(SD1), 80Sr(SD1), 81Sr(SD1), 82Sr(SD), 83Sr(SD), 84Zr(SD), 86Zr(SD1), 86Zr(SD4), 87Nb(SD2), 89Tc(SD) and 91Tc(SD) nuclei. The VMI model brings very comprehensive interpretation for spin assignment and to study the properties of SD bands in light mass region nuclei.

Temporal characterization of fundamental plasma parameters in pulsed liquid electrode plasma (LEP) optical emission spectrometry

The fundamental characteristics of liquid electrode plasma (LEP), a pulsed plasma source for optical emission spectrometry, were investigated. Two distinct phases were observed during the process of pulsed plasma generation, namely bubble generation and active plasma discharge. The ionization efficiency of the LEP, with Mg as a representative analyte, was gauged from the ratio of Mg II 279.553 nm to Mg I 285.213 nm emission and was found to increase from about 5% to 20% in a close-to-linear fashion with the discharge voltage from 800 V to 1200 V. The Mg II/Mg I ratio of the LEP was 2.5 to 3 orders of magnitude less than that typically offered by an inductively coupled plasma (ICP) but was comparable to other solution-based glow discharges. It was found that an off-time interval of more than 150 ms between successive discharge pulses was required to obtain a stable pulse-to-pulse discharge current. Temporally resolved emissions of Mg II 279.6 nm, Mg I 285.2 nm, Fe I 373.5 nm, OH band head at 306 nm, and Hα line at 656.3 nm showed that the background species (OH band and Hα line) reached their maximum emission intensities at around 0.5 ms to 0.7 ms with respect to the onset of the discharge pulse whereas the maximum emissions were observed between 0.7 ms to 0.9 ms for analyte species (Mg and Fe lines). The electron density observed in the present work was in the range from 5.7 × 1015 cm−3 to 8.2 × 1015 cm−3, which was similar to those found in an analytical ICP. The temporal averaged OH rotational temperature was 3300 K, which was comparable to the values of an analytical ICP and solution-based glow discharges. By contrast, the temporally averaged Fe I excitation temperature was around 8900 K, which was even higher than that of an analytical ICP and roughly triple the values obtained by techniques based on glow discharge of liquid samples.

Electronic transitions in Rb2+ dimers solvated in helium

We have measured depletion spectra of the heteronuclear (85Rb87Rb+) dimer cation complexed with up to 10 He atoms. Two absorption bands are observed between 920 and 250 nm. The transition into the repulsive 12Σu+ state of HeRb2+ gives rise to a broad feature at 790 nm (12,650 cm−1); it exhibits a blueshift of 98 cm−1 per added He atom. The transition into the bound 12Πu state of HeRb2+ reveals vibrational structure with a band head at ≤ 15,522 cm−1, a harmonic constant of 26 cm−1, and a spin–orbit splitting of ≤ 183 cm−1. The band experiences an average redshift of − 38 cm−1 per added He atom. Ab initio calculations rationalize the shape of the spectra and spectral shifts with respect to the number of helium atoms attached. For a higher number of solvating helium atoms, symmetric solvation on both ends of the Rb2+ ion is predicted.

Intriguing detection of 12CO molecular emission in a classical Be star

Context. In the group of B stars with spectroscopic peculiarities, we can find the Be and the B[e] stars. The Be stars are early-type rapid rotators that present, as their principal characteristic, emission lines of hydrogen and singly ionized metals due to the presence of a gaseous envelope. The B[e] stars present in their spectra heterogeneous features that reveal the presence of regions with very different properties in a gaseous and dusty envelope. Aims. Our goal is to study the evolution of the disks around peculiar B stars through the variability of their physical properties and dynamical structure, as well as to set constraints on different models and disk forming mechanisms. Methods. Throughout the last decade, we have carried out temporal monitoring of a sample of objects in the near infrared using spectroscopic facilities at the Gemini and Las Campanas Observatories. In the present work, we focus on the classical Be star 12 Vul, for which also optical spectra have been collected quasi-simultaneously. Results. We observed variability in the hydrogen line profiles of 12 Vul, attributed to dissipating and building-up processes of the circumstellar envelope. Also, we found that this Be star presented the 12CO band heads in emission in one observation. The emission of this molecule has not been previously reported in a Be star, while it is a common feature among B[e] stars. We obtained parameters to describe the 12CO emitting region and propose different scenarios to explain this intriguing emission.

Extension at the downstream end of turbulent band in channel flow

In this Letter, the velocity structures and the extension behavior of localized turbulent bands in channel flows are measured by particle image velocimetry in a plane parallel to the walls and are analyzed by comparing with direct numerical simulations at low Reynolds numbers. It is illustrated that the convection velocity of the band head (band’s downstream end) is not determined by the formation and propagation of low-speed streaks but by a high-speed “hat” shaped region near the band head. This “hat” region travels downstream obliquely like a solitary wave and leaves newly generated low-speed streaks to travel slowly in the spanwise direction, leading to the head extension of turbulent bands.

Effective field theory for deformed odd-mass nuclei

We develop an effective field theory (EFT) for deformed odd-mass nuclei. These are described as an axially symmetric core to which a nucleon is coupled. In the coordinate system fixed to the core the nucleon is subject to an axially symmetric potential. Power counting is based on the separation of scales between low-lying rotations and higher-lying states of the core. In leading order, core and nucleon are coupled by universal derivative terms. These comprise a covariant derivative and gauge potentials which account for Coriolis forces and relate to Berry-phase phenomena. At leading order, the EFT combines the particle-rotor and Nilsson models. We work out the EFT up to next-to-leading order and illustrate the results in $^{239}$Pu and $^{187}$Os. At leading order, odd-mass nuclei with rotational band heads that are close in energy and differ by one unit of angular momentum are triaxially deformed. For band heads that are well separated in energy, triaxiality becomes a subleading effect. The EFT developed in this paper presents a model-independent approach to the particle-rotor system that is capable of systematic improvement.

Analysis of the TiO isotopologues in stellar optical spectra

Context. We used the new ExoMol TiO rovibronic line lists to identify and model TiO isotopologue features in spectra of M dwarfs. Aims. We investigate problems involving the computation of electronic bands for different isotopologues of TiO by modelling optical spectra of late-type stars. Based on this, we determine their Ti isotopic abundances and compare the TiO isotopologue spectra computed using line lists by different authors. Methods. We fitted theoretical synthetic spectra to the observed stellar molecular bands of TiO. We modelled spectra of two M dwarfs, GJ 15A (M1V) and GJ 15B (M3 V), to determine Ti isotopic ratios in their atmospheres. Results. We demonstrate the accuracy of the ExoMol TOTO line list for different isotopologues of TiO and the possibility of determining accurate Ti isotope abundances in a number of spectral ranges. The 7580–7594 Å spectral range seems particularly useful, with two atomic lines of Fe I and molecular band heads of 50Ti O, 49Ti O, 48Ti O, and 47Ti O clearly observable in our two M-dwarf spectra. We determine non-solar Ti isotopic ratios of 46Ti, 47Ti, 48Ti, 49Ti, and 50Ti of 7.9, 5.2, 72.8, 7.9, and 6.2 for GJ 15A and 7.4, 4.2, 76.6, 5.8, and 6.0 for GJ 15B with an accuracy of ±0.2. [Ti] = 0.040 and 0.199 and within an accuracy of ±0.10 were also determined for GJ 15A and GJ 15B, respectively. Conclusions. We find that the ExoMol TOTO TiO line list (a) describes the fine details in line position and intensity of the M-dwarf spectra better than other available TiO line lists, (b) correctly reproduces the positions and intensities of the TiO isotopologue band heads observed in M-dwarf spectra, and (c) can be used to determine Ti isotope abundances in atmospheres of M stars.

Microscopic study of band structures of neutron-rich 153,155,157Sm isotopes

A systematic study of band structures of some odd mass Samarium isotopes with neutron numbers 91 ≤ N ≤ 95 is carried out by employing projected shell model. The theoretical results have been obtained for band head energies, energy spectra, transition energies and moment of inertia. The calculations on comparison with the experimental data show a reasonably good agreement. The band spectra and transition energies for higher spin states are also predicted in these isotopes. The calculations successfully provide good understanding of the change in structure of the yrast bands and excited bands in terms of single and multi-quasiparticle configurations. The future experimental work will test the predictions made in this paper.

Dynamical Symmetries in Shell and Collective Models of Nuclear Structure

The dynamical symmetries in the algebraic shell model and the collective Interacting Vector Boson Model (IVBM) realized in terms of fermion and boson creation and annihilation operators are investigated. The obtained analytic eigen-energies in both models are compared with the experimental ones and the strengths of the corresponding terms of the model Hamiltonians are evaluated in both cases. In the algebraic realization of the Pairing plus Quadrupole Shell Model the correlations and transition between the quadrupole and pairing phases—dynamical symmetries are investigated in application to nuclear systems in the first few light shells. In the symplectic extension of the IVBM the spectra of heavy even-even nuclei with transitional between rotational and vibrational character is well reproduced. The algebraic connections between dynamical symmetries of the nuclear collective spectra and the ordering of the low-lying states with fixed angular momentum permits a reasonable and experimentally proved prediction of the position of the 0+ band heads of the collective bands. The models based on dynamical symmetries give an elegant and simple way to describe the complex spectra of nuclei with different shapes.

Positive-Parity Linear-Chain Molecular Band in ^{16}C.

An inelastic excitation and cluster-decay experiment ^{2}H(^{16}C,^{4}He+^{12}Be or ^{6}He+^{10}Be)^{2}H was carried out to investigate the linear-chain clustering structure in neutron-rich ^{16}C. For the first time, decay paths from the ^{16}C resonances to various states of the final nuclei were determined, thanks to the well-resolved Q-value spectra obtained from the threefold coincident measurement. The close-threshold resonance at 16.5MeV is assigned as the J^{π}=0^{+} band head of the predicted positive-parity linear-chain molecular band with (3/2_{π}^{-})^{2}(1/2_{σ}^{-})^{2} configuration, according to the associated angular correlation and decay analysis. Other members of this band were found at 17.3, 19.4, and 21.6MeV based on their selective decay properties, being consistent with the theoretical predictions. Another intriguing high-lying state was observed at 27.2MeV which decays almost exclusively to ^{6}He+^{10}Be(∼6 MeV) final channel, corresponding well to another predicted linear-chain structure with the pure σ-bond configuration.