Effect of phasons and magnetic fields on the electronic spectrum of a three-dimensional quasicrystal

The effect of phasons and magnetic fields on the electronic spectrum of an icosahedral quasicrystal is investigated in the tight-binding approximation. Phasons smooth the singular spectrum and produce a greater delocalization of the critical wave functions. A magnetic field shifts the limits of the spectrum, smooths the spectrum, lifts the degeneracy, and also delocalizes the wave functions. Pis’ma Zh. éksp. Teor. Fiz. 69, No. 9, 659–661 (10 May 1999)     

Structural and electronic properties of Danzer's model of a three-dimensional quasicrystal

By using deflation rules, the coordinates of the atoms in Danzer's model of a 3d quasicrystal are computed. The resulting atomic positions in a cut through the model well agree with experimental findings. Furthermore, for Danzer's model the static structure factor, the pair correlation function, and properties of a tight binding electron model are studied. The electron density of states shows a characteristic peak at energyE=O, which may be associated to confined states.     

Stochastic web as a generator of three-dimensional quasicrystal symmetry

It is shown that two coupled oscillators perturbed by periodic kicks generate a thin stochastic web in the four-dimensional phase space, which differs from the Arnold web. Under some resonance-type condition the web possesses a quasicrystal-type symmetry. In three-dimensional coordinate space, the web's symmetry corresponds to the icosahedral one and, due to that, the original four-dimensional map can be considered as a dynamical generator of the quasicrystal-type tiling of three-dimensional space.     

The electronic spectrum of benzvalene

A detailed investigation of the electronic spectrum of benzvalene [tricyclo (3.1.0.0^2,6)hex-3-ene] in the vapor phase is reported. The spectrum appears to consist of two overlapping electronic transitions above 200 nm. The lower energy transition is broad and structureless, has an onset near 285 nm, and is assigned as ${}^1\text{B}{}_2\text{←}{}^1\text{A}{}_1$. The second transition, showing forbidden vibronic structure based on two false origins near 226 nm, is assigned ${}^1\text{A}{}_2\text{←}{}^1\text{A}{}_1$. The ¹A₂ state presumably arises from a $\text{σπ}{}^1$ configuration, which indicates significant ring strain and/or σ-π interaction. A one-state assignment of the spectrum is also possible.     

The electronic spectrum of Dewar benzene

The electronic spectrum of Dewar benzene [bicyclo (2.2.0) hexa-2,5-diene] consists of two transitions above 185 nm. The lower energy transition is structureless and broad with a maximum at 205 nm. The other system begins around 200 nm and shows initially well-defined vibronic structure on a background of increasing continuous absorption, but becomes structureless by 185 nm. Arguments are presented that the two excited states involved in the spectrum are ¹A₂ arising from a $\text{π-π}{}^1$ excitation, and ¹B₁ from a $\text{σ-π}{}^1$ excitation involving the strained σ-bridge bond in Dewar benzene. The interrelationships both photochemical and photophysical of the (CH)₆ potential surface are discussed.     

The electronic spectrum of gaseous SnS

Observations of the spectrum of SnS excited in chemiluminescence have led to the characterization of two low-lying excited states of SnS, $\text{a}\text{Ω}\text{1(}{}^3\text{Σ}{}^{\mathrm{+}}\text{)}$, with T_e = 18 143.9 cm^?1, and $\text{A0}{}^{\mathrm{+}}\text{(}{}^3\text{Π}\text{)}$, with T_e = 22 021.3 cm^?1. Extended rotational analyses of the perturbed bands observed in the absorption spectrum enable assignments to be suggested for the components $\text{Ω}\text{0}{}^{\mathrm{+}}$ and 1 of ³Σ^? and $\text{Ω}\text{1}$ of ³Π.     

The electronic emission spectrum of SiB

The gas phase spectrum of the silicon boride radical has been observed for the first time. Two electronic transitions were observed in emission from a corona excited supersonic expansion source. The D⁴Σ⁻-X⁴Σ⁻ system consists of emission from v′ = 0 to v″ = 0-3, while the A⁴Π-X⁴Σ⁻ system consists of numerous bands with v′ = 0-5 and v″ = 0-11, although only the strong 0-0 and 0-1 bands have been analyzed so far.     

The electronic spectrum of silicon monotelluride radical

In the electronic spectrum of silicon monotelluride which has been produced in microwave discharges through sealed tubes, a large number of new bands belonging to theA ¹Π-X ¹Σ⁺ system (3100–3900 Å) and theE ¹Σ⁺-X ¹Σ⁺ system (2800–3100 Å) of Si¹³⁰Te has been observed. The vibrational structure analyses of these band systems have resulted in the determination of improved vibrational constants in all the three electronic states involved in these transitions. An error in the previous determination of the vibrational constants of theE ¹Σ⁺ state has been corrected. An upper limit for the dissociation energy of the silicon monotelluride has been determined to be 40,000 cm^?1.     

准晶的发现

准晶是20世纪80年代发现的有着广泛应用前途的新材料.它的问世,拓宽了物理学、材料科学和数学的研究领域,更新了对固体特别是晶体的认识.本文记叙了准晶发现的历史过程;论述了准晶发现的科学意义;扼要地介绍了准晶的发现者Dan Shechtman教授.     

The electronic Raman spectrum of cobalt doped MgO

The energies of the ⁴T_1g states of Co²⁺ as a dilute substitutional impurity in MgO relative to the ground Λ_6g doublet have been found by low temperature Raman spectroscopy to be two Λ_8g states at 305 ± 3 cm^?1 and 930 ± 3 cm^?1; the remaining Λ_7g energy is predicted to be in the 980–1010 cm^?1 range the corresponding Λ_6g → Λ_7g Raman transition being weak and buried in the extensive two-phonon background. A second-order perturbation calculation which couples the spin-orbit states to both E_g and T_2g modes of vibration gives a weak but important Jahn-Teller stabilization energy for the Λ_8g states.     

The electronic spectrum of tantalum hydride and deuteride

The diatomic molecule tantalum hydride (TaH) and its isotopologue tantalum deuteride (TaD) have been detected for the first time by laser excitation spectroscopy. The gas-phase molecules were produced in a hollow cathode discharge. Two red-degraded bands, one arising from TaH at 636 nm and the other from TaD at 635 nm, have been recorded at sub-Doppler resolution by intermodulated fluorescence spectroscopy. A rotational analysis shows that both bands are Ω = 2←2 in character, with well-resolved Ω-doubling in the upper state of TaH. Analysis of the ¹⁸¹Ta magnetic dipole and electric quadrupole hyperfine structure reveals that the lower X³Φ₂ electronic state of the two transitions arises from a σ²πδ electronic configuration, in agreement with previous theoretical calculations. The bond length in the TaH X³Φ₂ (v = 0) level is found to be 1.756960(4) Å.     

The electronic spectrum of PN. A configuration interaction study

Potential energy curves were calculated for the ground state of PN and for all excited singlet and triplet states resulting from the 2π → 3π, 7σ → 3π, 2π → 8σ, and 7σ → 8σ orbital excitations. CI studies at 4 Å served to establish dissociation energies. Spectroscopic constants were calculated, and are in good agreement with those of the known X¹Σ⁺ and A¹Π states. Overall, their similarity with those observed for N₂ is striking. Various states considered to perturb the known excitations are discussed. The recently discovered second ¹Σ⁺ state is included.     

Rotationally resolved electronic spectrum of propadienylidene

The rotationally resolved electronic spectrum of a vibrational band in the transition of the cumulene carbon chain C₃H₂ was measured in the 625 nm region in a supersonic discharge using cw cavity ring down spectroscopy. The rotational structure was analysed using a conventional Hamiltonian for an asymmetric top molecule, and the constants A′, B′, and C′ in the upper state were determined. The observed band is assigned to a combination of a₁ and b₂ vibrations with the frequency around 2000 cm⁻¹. The geometries in the ¹A₁, ¹A₂, ¹B₁ states and the intersection point between the latter two were obtained using ab initio calculations. The effective structure in the measured vibrational level of the ¹A₂ state was inferred from the determined constants.     

The fine structure of the spectrum of the electronic NO laser

The spectrum of the electronic NO laser has been photographed with high resolution in the region 10 100–10 500 Å. It shows the band system F²Δ-C²Π whose upper and lower states are both Rydberg states configurationally mixed with valence states. Only predissociated rotational levels of the lower state appear in the spectrum. For v = 0 of C²Π a single mixed level $\text{T}{}_{\mathrm{y}}\text{(J = 5}\text{1}\text{2}\text{) = 52431}\text{cm}{}^{\mathrm{?1}}$, very close to the dissociation limit, gives rise to laser lines.