Magnetic field effect on the H2CS fluorescence from the first excited singlet state Ã1A2

Fluorescence intensity in thioformaldehide vapours (H₂CS), excited to the ÃA₂ different vibronic levels of the ùA₂ ? [Xtilde]¹A₁ transition, were measured as a function of an external magnetic field. On excitation to these levels, dynamics in zero and non-zero field may be described in the small-molecule limit, with fluorescence exhibiting an almost exponential decay. A magnetic field changes the integrated intensity and decay lifetime of the thioformal-dehide fluorescence induced from different vibronic levels of the ù A₂ state. We found that the magnetic field effect grows at lower gas pressures. The measured field dependences of the magnetic field effect can be fitted using field-saturated functions. The measured data were explained by the indirect mechanism theory (nuclear-spin and electron-spin decoupling mechnism).     

Observation of the fast component in the fluorescence of gaseous SO2 excited to the A1A2 state in the presence of a magnetic field

Effects of an external magnetic field (B) on the SO₂ fluorescence have been examined under excitation of the ‘C’ band and the single rotational levels of the ‘B’ and ‘E’ bands of the A(¹A₂) ← X¹A₁ transition. For the ‘C’ band, the total SO₂ fluorescence was studied, while for excitation of the single rotational levels, fluorescence of the single rotational lines of (^rR₅(5) (31711 cm^-1), ^pP₇(7) (31662 cm^-1)) (‘E’ band) and of (^rR₈(8) (31000 cm^-1), ^pP₁₀(10) (30927 cm^-1)) (‘B’ band) was studied. Decay of the SO² fluorescence was studied with nanosecond time resolution in the 1?5–50 mTorr region. In the presence of a magnetic field, decay of the total SO₂ fluorescence and of the fluorescence belonging to the single rotational lines were fitted by the bi-exponential functions. In the case of the total SO₂ fluorescence, this function also includes the time independent term, which, however, is dependent on a magnetic field. The time independent term belongs to the long-living component, which can be approximated by a constant in the time-scale studied. Radiationless processes induced by an external field were directly observed. The magnetic field and pressure dependences of the processes induced by a field were studied under excitation of the SO₂ fluorescence by light of a different wavelength. The data obtained were explained by the direct mechanism.     

Ab initio MRD-CI investigation of the electronic spectrum of glyoxal (CHO)2

Multireference configuration interaction (MRD-CI) calculations are used to compute the electronic spectrum of glyoxal (CHO)₂, a key species in atmospheric chemistry. The calculations place the first dipole-allowed transition 1¹A_u←X¹A_g at 2.80?eV (442.8?nm) with an oscillator strength of 0.0002 and the dipole forbidden 1¹B_g?←?X¹A_g transition at 4.22?eV (293.8?nm), in accordance with prior experiments. In addition, a much stronger transition (3¹B_u?←?X¹A_g) at 8.51?eV (145.7?nm) is predicted, which has not yet been reported in the literature. This transition corresponds to 1b_g?→?2a_u excitation and can be characterized as π(CO)?→?π?(CO) type in accordance with the computed relatively large oscillator strength f?=?0.38. The corresponding triplet states are also computed.     

Rotational band contour analysis in the Ã1A′-[Xtilde]1A′ electronic systems of substituted naphthalenes

The 0₀ ⁰ bands of the à ¹ A′-[Xtilde] ¹ A′ systems of 1-fluoro, 1-hydroxy and 1-aminonaphthalene have been investigated by rotational band contour analysis. The 0₀ ⁰ bands in 1-fluoro and 1-hydroxynaphthalene are 70 per cent type A and 30 per cent type B, and 75 per cent type A and 25 per cent type B hybrids respectively: the electronic transition moment vector has been rotated by about 15° towards the carbon atom C₃ by the F and OH substituents compared to naphthalene (in which, in the Ã-[Xtilde] system, it is along the long in-plane axis). In 1-aminonaphthalene it seems likely that the 0₀ ⁰ band is predominantly type A, but it could not be observed with sufficient intensity to be able to obtain the excited state rotational constants with any certainty.     

Identification of two Ag‐2,2′:6′,2″‐terpyridine surface species on Ag nanoparticle surfaces by excitation wavelength dependence of SERS spectra and factor analysis: evidence for chemical mechanism contribution to SERS of Ag(0)–tpy

Measurement and interpretation of the excitation wavelength dependence of surface‐enhanced Raman scattering (SERS) spectra of molecules chemisorbed on plasmonic, e.g. Ag nanoparticle (NP) surfaces, are of principal importance for revealing the charge transfer (CT) mechanism contribution to the overall SERS enhancement. SERS spectra, their excitation wavelength dependence in the 445–780‐nm range and factor analysis (FA) were used for the identification of two Ag‐2,2′:6′,2″‐terpyridine (tpy) surface species, denoted Ag⁺–tpy and Ag(0)–tpy, on Ag NPs in systems with unmodified and/or purposefully modified Ag NPs originating from hydroxylamine hydrochloride‐reduced hydrosols. Ag⁺–tpy is a spectral analogue of [Ag(tpy)]⁺ complex cation, and its SERS shows virtually no excitation wavelength dependence. By contrast, SERS of Ag(0)–tpy surface complex generated upon chloride‐induced compact aggregate formation and/or in strongly reducing ambient shows a pronounced excitation wavelength dependence attributed to a CT resonance (the chemical mechanism) contribution to the overall SERS enhancement. Both the resonance (λ_exc = 532 nm) and off‐resonance (λ_exc = 780 nm) pure‐component spectra of Ag(0)–tpy obtained by FA are largely similar to surface‐enhanced resonance Raman scattering (λ_exc = 532 nm in resonance with singlet metal to ligand CT (¹ MLCT) transition) and SERS (λ_exc = 780 nm) spectra of [Fe(tpy)₂]²⁺ complex dication. Copyright © 2014 John Wiley & Sons, Ltd.     

Rotational band contour analysis in the à 1 A′-[Xtilde] 1 A′ electronic systems of substituted naphthalenes

The 0₀ ⁰ bands of the à ¹ A′-[Xtilde] ¹ A′ electronic systems of 2-fluoro, 2-hydroxy- and 2-aminonaphthalene have been identified and then rotationally analysed by the method of rotational band contour analysis. The effect of 2-substitution on the direction of the electronic transition moment vector in naphthalene is found to be drastic: the vector is oriented by about 70–80° (anti-clockwise in figure 1) by the substituent. However, the orientation is almost unaffected by the nature of the substituent.

The 0₀ ⁰ bands are all type A, B hybrids but predominantly type B. Significant differences in the 0₀ ⁰ band rotational contours in the three molecules are reflected in the different values of ΔA, ΔB and ΔC found from the contour analyses. An attempt to interpret the changes of rotational constants in terms of changes in geometry from the ground to the excited state suggest very strongly that the geometry change of the naphthalene rings in all the molecules is similar to that in naphthalene itself but that the carbon-substituent bonds contract in the excited state. The contraction increases from F to OH to NH₂ and is probably quantitatively similar to that suggested previously for the corresponding monosubstituted benzenes.     

The Rotational Analysis of the Five new Vibronic Bands of No2 in the Range 5050-5200 Å

The five new vibrational bands in the range 5050-5200 Å of the laser induced fluorescence excitation spectra of NO₂ were measured and rotationally assigned at room temperature. Though the spectra were rather congested, we can determine the band origins, and rotational and spin-rotation constants for these bands. All rotational structures analyzed are of the parallel type. It was shown that the electronic excited state òB₂ were heavily perturbed by the high lying vibration levels of ground state [Xtilde] ² A ₁ and that the interactions between these two electronic states was the main rationale for the complexity of NO₂ visible spectra.     

Neutrino radiation by an electon in quantizing nuclear and strong magnetic fields

The probability and intensity of neutrino radiation of a hydrogen-like atom in the strong magnetic field B >> Z ²α² B ₀, α = e ² = 1/137, B ₀ = m ²/e = 4.41⋅10¹³ G are determined. The temperature dependence of the intensity of an atom ensemble is analyzed.     

Pre-resonant Raman scattering in antracene crystals

The pre-resonant Raman scattering (PRRS) of anthracene crystals (T = 4.2?30 K) has been studied. A tunable dye laser (v_exc = 25000?25100 cm^-1 was used to produce an excitation close to the lowest exciton band bottom (v₀ = 25097 cm^-1). A sharp increase of the PRRS intensity when approaching the excitation light frequency v_exc to v₀ and then the not less sharp drop of the PRRS intensity close to resonance (v₀ ? v_exc ≈ 35?15 cm^-1) where observed. An extremely high PRRS sensitivity to temperature and the excitation light intensity was found. The results are explained within the framework of stimulated PRRS in anthracene crystals.     

Mössbauer study of the spinel system GexCu1−xFe2O4

The magnetic properties of the spinel series Ge_xCu_1?xFe₂O₄ (X = 0 to 0.8) have been investigated by means of Mössbauer spectroscopy. Mössbauer spectra for X = 0.0 to 0.6 suggest the existence of two hyperfine fields, one due to the Fe³⁺ tetrahedral ions (A-sites) and the other due to Fe³⁺ octahedral ions (B-sites), while for X = 0.8 it shows the superposition of hyperfine field split spectra from A- and B-site ions and a broad central line spectrum. For 0.2 ? X ? 0.4, fast electron exchange among octahedral iron ions occurs as in Fe₃O₄. The variations of nuclear magnetic fields at the A- and B-sites are explained on the basis of AB and BB supertransferred hyperfine interactions.     

Doppler-free two-photon absorption spectroscopy of trans-glyoxal under magnetic fields up to 6T

In order to measure the Doppler-free two-photon absorption (DFTPA) spectrum in the presence of a strong magnetic field, a sample cell placed in an optical resonator was installed at the centre of the bore of a superconducting magnet capable of generating a magnetic field of up to 6T. Changes in spectra of the A ¹A_u ← X ¹A_g transition of trans-glyoxal were measured as a function of magnetic field strength. Level crossings induced by Zeeman energy shifts were observed. The perturbing level, which shows hyperfine splitting, was identified as the ³A_u(nπ?) state, because the hyperfine splitting is small in the ³B_u(^ππ?) state and large in the ³A_u(nπ?) state. The perturbation between the A ¹A_u(nπ?) and ³A_u(nπ?) states was shown to take place by either vibronic interaction or Zeeman interaction between the ³A_u(nπ?) state and the ³B_u(ππ?) component mixed to the A ¹A_u(nπ?) state by spin-orbit interaction. The magnetic moment of the A ¹A_u state was determined to be approximately 0.0028μ_B, and the magnitude of the mixing coefficients 〈1 ³B_u|H _so|1 ¹A_u〉/[E(1 ¹A_u) ? E(1 ³B_u)] was evaluated to be 0.026.     

Unravelling the visible spectrum of strontium monomethoxide

The bands of the A²E–X²A₁ and B²A₁–X²A₁ electronic transitions of SrO¹²CH₃ and the B²A₁–X²A₁ transition of SrO¹³CH₃ have been recorded at high resolution using a laser ablation jet source. The optical–optical double resonance population depletion technique was used to facilitate the assignment of the spectra. Rotational levels with K = 0, ±1 in the X²A₁ and B²A₁ states and K = 0, 1 and 2 in the A²E state have all been characterised. A perturbation affecting the B²A₁ state caused a reversal of the ordering of the spin-rotation components, F₁ and F₂, in the SrO¹²CH₃ isotopologue. This required the introduction of a modified rotational constant B_mod, affecting only the K = 1, F₂ component of the B²A₁ state, in order to model the SrO¹²CH₃ data in a global fit of the A²E–X²A₁ and B²A₁–X²A₁ transitions.     

Spin diffusion effects on E.S.R. linewidths in the quasi-two-dimensional magnetic system bis[1,2-bis(2-methoxyethoxy)ethane] sodium biphenylide

The electron spin resonance absorption line of a single crystal of the quasi-two-dimensional system bis[1,2-bis(2-methoxyethoxy)ethane] sodium biphenylide has been investigated. Experiments are performed at 9·4 GHz (X-band) and at 0·0332 GHz (B ₀ ≈ 1·1 mT). Only at X-band does the linewidth have a (3 cos² ? - 1)² angular dependence (? is the angle between the magnetic field and the normal to the two-dimensional magnetic plane). The linewidth is frequency dependent especially at the magic angle (? = 54° 44′). The results are interpreted with the linewidth theory of Richards and Salamon. For both frequencies good agreement exists between experimental and theoretical results, proving the importance of spin diffusion in the long time behaviour of the spin correlation functions.     

N-lines in the luminescence spectra of Cr3+-doped spinels: IV. Excitation spectra

Excitation spectra (T = 75–300 K; λ_exc = 450–630 nm) which were measured for the R-lines of Cr³⁺-doped oxides (α-Al₂O₃, β-Ga₂O₃) and for different luminescence lines (R-lines, N-lines) of Cr³⁺-doped spinels (MgAl₂O₄, ZnAl₂O₄, ZnGa₂O₄) are reported. The excitation maxima observed for different luminescence lines of a given compound exhibit considerable differences: 530 nm ? λ^max_exc ? 565 nm for MgAl₂O₄; 530 nm ? λ^max_exc ? 580 nm for ZnAl₂O₄; 545 nm ? λ^max_exc 555 nm for ZnGa₂O₄. According to the interpretation of N-lines to arise from different classes of Cr³⁺ ion swith different short range orderd, the excitation maximum of one distinct line should entirely correspond to the transition Δ : ⁴T₂ ← ⁴A₂ of that Cr³⁺ class from which the line arises. By this method spectroscopic data about the different kinds of Cr³⁺ ions present in a given sample can, therefore, be obtained which are not available from absorption measurements. The experimetal data were found to be in agreement with the results of model calculations. Restrictions which limit the accuracy and relevance of the data are discussed.     

Half-field and normal electron spin resonance study of the quasi-two dimensional magnetic crystal Mn(CHOO)2·2H2O

We have studied the normal electron spin resonance at the Larmor frequency as well as the half-field resonance of the quasi two dimensional magnetic crystal Mn(CHOO)₂·2H₂O at 35 GHz and room temperature. There are two groups of Mn²⁺ ions referred as A and B in this compound. The A ions lie in parallel (100) planes and have a strong exchange interaction within the plane. On the other hand, the B ions which lie in the adjacent parallel planes have no exchange interaction in the plane. We have measured the line width of the normal resonance from the A ions as a function of θ and φ where θ is the angle between the d.c. magnetic field H₀ and the a-axis of the crystal, which is very nearly perpendicular to the (100) plane and φ is the azimuthal angle of H₀ in the bc plane with respect to the b-axis. We also measured the intensity of the half-field resonance as a function of φ. We have calculated the second moments of the normal resonance line as a function of θ and φ. There is a satisfactory agreement between the calculated and the observed θ dependence of the line widths. The intensity of the half-field resonance has a maximum at φ = 40° whereas in an ideal 2d magnet, the maximum intensity is expected at φ = 45°. The ESR line width, because of the spindynamics in a 2 dimensional magnetic crystal, has an angular dependence of the form (3 cos²θ ? 1)². The observed dependence of the line width in Mn(COOH)₂·2H₂O seems to follow the same angular dependence when corrected for the contribution from the nearest neighbor B ions.     

Photoluminescence and gain spectroscopy of highly excited epitaxial GaN-layers

The spectra of photoluminescence and optical gain of GaN have been measured at low temperatures under N₂-laser excitation.At low excitation levels (I _exc10⁴W cm^–2) we observe free and bound exciton recombination. At intermediate excitation (I _exc10⁵W cm^–2), inelastic exciton-exciton scattering processes show up. At the highest excitation levels (I _exc10⁶ W cm^–2) we report here for the first time the emission from an electron-hole plasma.     

The spin-isospin decomposition of the nuclear symmetry energy from low to high density

The energy per particle BA in nuclear matter is calculated up to high baryon density in the whole isospin asymmetry range from symmetric matter to pure neutron matter.The results,obtained in the framework of the Brueckner-Hartree-Fock approximation with two-and three-body forces,confirm the well-known parabolic dependence on the asymmetry parameterβ=(N?Z)/A(β^2 law)that is valid in a wide density range.To investigate the extent to which this behavior can be traced back to the properties of the underlying interaction,aside from the mean field approximation,the spin-isospin decomposition of BA is performed.Theoretical indications suggest that theβ^2 law could be violated at higher densities as a consequence of the three-body forces.This raises the problem that the symmetry energy,calculated according to theβ^2 law as a difference between BA in pure neutron matter and symmetric nuclear matter,cannot be applied to neutron stars.One should return to the proper definition of the nuclear symmetry energy as a response of the nuclear system to small isospin imbalance from the Z=N nuclei and pure neutron matter.     

Mossbauer study of the Cu-Cd ferrite system

The magnetic properties of the Cd_xCu_1?xFe₂O₄ ferrite system (x = 0 to 1) have been investigated by means of Mossbauer Spectroscopy. Mossbauer Spectra for x = 0.0 to 0.6 suggest the existence of two hyperfine fields, one due to the Fe³⁺ tetrahedral ions (A-sites) and the other due to Fe³⁺ octahedral ions (B-sites), while for x = 0.7 it shows relaxation behaviour and for x ? 0.8 it exhibits a paramagnetic quadrupole doublet. The systematic dependence of the isomer shift, quadrupole interactions and nuclear fields of ⁵⁷Fe³⁺ ions in both A- and B-sites has been determined as a function of cadmium content. The variation of nuclear magnetic fields at the A- and B-sites are explained on the basis of A-B and B-B supertransferred hyperfine interactions. Analysis of the relaxation spectrum observed at x = 0.7 (300 K) suggests that the relaxation mechanism is due to domain wall oscillations. It has been found here that the QS increases from CuFe₂O₄ as the cadmium concentration is increased.     

磁畴壁在复合外场中的运动方程及其在磁弹性内耗的应用

在以速率α匀速增加的磁化场中,测量铁磁性材料的内耗时,材料中畴壁所受的力除了外加磁化场所提供的主驱动力A₀⁰+A₁⁰αt,以及测量内耗所用交变应力所提供的微扰交变驱动力A₃⁰sinωt之外,经分析表明,还存在一项在数值上与主驱动力及交变驱动力的乘积成正比的交互作用驱动力,可写为A₂⁰sinωt。这里的A₀关键词：