Two-photon ionization spectrum of the 1Lb ← S0 transition in toluene

The multiphoton ionization (MPI) spectrum of toluene arising from the ¹B₂ (¹L_b) valence state has been investigated. The state participates as a two-photon resonance. A total of nine excited state fundamentals have been characterized, including three non-totally symmetric vibrations. The toluene MPI spectrum shows a strong resemblance to the two-photon fluorescence excitation spectrum with the strongest transitions taking place to the origin and excited state modes ν₁(a₁), ν₁₂(a₁) and ν₁₄(b)₂). The intensities of the observed fundamentals are rationalized in terms of Franck-Condon and vibronic coupling effects. A major conclusion is, that the primary mechanism for the activity of ν₁₂ is vibronic coupling.     

Forbidden Raman bands of Sf6: collision induced Raman scattering

The frequencies, relative scattering cross sections and depolarizations ratios of forbidden fundamental and overtone Raman bands have been measured for the first time in the gaseous state. The absolute scattering cross sections of the allowed bands of gaseous SF₆ are given as well. The characteristic density dependence of the scattering cross sections of the forbidden fundamentals is explained in terms of collision induced Raman scattering. There is evidence for frame distortion of the molecules during the collision.     

Vibrational spectrum of RbVOPO4

The infrared and Raman laser spectra of RbVOPO₄ were recorded and briefly discussed with the aid of factor group analysis. Some comparisons with the spectra of related materials were also made.     

Theory of the S0 → S1 two-photon transition in benzene

The symmetry forbidden two-photon excitation spectrum recently observed in benzene vapour gave intensities inverted from those expected by current predictions based on the Herzberg-Teller theory for vibronic induced processes. We show that an extension of the HT approximation which allows us to correlate the movement of electrons and nuclei leads to an agreement with the experimental results.     

On the phase transition of acetylene-d2

The solid-solid phase transition of acetylene-d₂ at 149 ± 1 K was investigated using a thermal neutron powder diffraction technique. Due to a rapid recrystallization in the vicinity of the transition point the study of the kinetics of the transition was not successful.     

On the vibrational spectrum of C9, C11 and C13

The harmonic frequencies and infrared intensities of C₉, C₁₁ and C₁₃ have been calculated using SCF and complete active space SCF (CASSCF) methods. The ordering of the harmonic frequencies in C₉ is predicted wrongly unless at least the π HOMO and LUMO are included in the active space. Infrared intensities depend crucially on the size of the active space. For linear odd-numbered clusters C₁₃ and larger, the computed SCF spectrum is qualitatively wrong. The recent observation of a band near 1809 cm⁻¹ in the gas phase is explained using our CASSCF results on C₁₃.     

The hypersensitive Δg(σuδu) ← Σg transition of the uranyl ion

The Δ_g(σ_uδ_u) ← Σ_g(σ_u)² transition of the uranyl ion which corresponds to an electron transfer for a weakly bonding oxygen orbital to a non-bonding uranium 5f_±2 orbital has characteristics similar to so-called hypersensitive 4f-4f transitions of the lanthanide ions.     

High-pressure phase transition in LiBH4

The high-pressure phase transition from ambient pressure α-LiBH₄ to high-pressure β-LiBH₄ was observed by Raman spectroscopy and X-ray diffraction between 0.8 and 1.1 GPa. The phase boundary between these two phases was mapped over a large range of temperatures using thermal conductivity studies and differential thermal analysis. The structure of the high-pressure phase could not be identified due to small number of experimentally observed reflections, but it was shown that it is different from previously reported theoretical predictions.     

Picosecond time-resolved Sn← S1 absorption spectrum of the tetracyanobenzene-toluene complex

The time-resolved absorption spectrum of the lowest excitcd singlet state (S₁) over the range 3 — 10 ps after 0.5 ps pulse excitation of the charge-transfer complex of 1,2,4,5-tetracyanobenzene and toluene shows an evolution with a 5 ± 3 ps time constant due to changes in configurations of the complex in S₁ associated with the reorientational relaxation of the solvent.     

Laser-excitation spectrum of gas-phase CCl2

The gas-phase laser-induced fluorescence—excitation spectrum of dichlorocarbene (CCl₂) has been observed in the 498–534 nm spectral region. Sufficient resolution has been obtained to partially resolve the band structure arising from the symmetrical stretching and bending vibrations, which leads to vibrational parameters for these modes.     

Ferromagnetic-phase transition in the spinel-type CuCr2Te4

Ferromagnetic-phase transition in spinel-type CuCr₂Te₄ has been clearly observed. CuCr₂Te₄ is a telluride-spinel with the lattice constant , which has been synthesized successfully. The heat capacity exhibits a sharp peak due to the ferromagnetic-phase transition with the Curie temperature . This value of T_C corresponds exactly to that of the negative peak of dM/dT in low field of 1.0 Oe. The magnetic susceptibility shows the Curie-Weiss behavior between 380 and 650 K with the effective magnetic moment /Cr-ion and the Weiss constant . The low temperature magnetization indicates the spin-wave excitations, where the existence of first term of Bloch T^3/2 law and the next T^5/2 term are verified experimentally. This spin-wave excitation is detected up to approximately 250 K which is a fairly high temperature.     

The emmission spectrum of Br2 in argon

We have observed and identified positive ions produced in a spark discharge in SF₆ at high pressure. The ion species were found to be very sensitive to impurities. In purified SF₆ the ions were sulfur-rich and complex before reacting to form chemically stable long-lived products.     

Pressure-induced transition in Tl2MoO4

Tl₂MoO₄ has been studied under high-pressure by X-ray diffraction, Raman spectroscopy, and optical absorption measurements. A first-order phase transition is observed at 3.5±0.5 GPa. The nature (ordered vs. disordered) of the high-pressure phase strongly depends on the local hydrostatic conditions. Optical absorption measurements tend to show that this transition is concomitant with an electronic structure transformation. Prior to the transition, single crystal X-ray diffraction shows that pressure induces interactions between MoO₄ fragments and the Mo coordination number tends to increase. In addition, the stereoactivity of the lone-pair electrons on the three symmetrically independent Tl-sites is not uniform; while for two sites the stereoactivity decreases with increasing pressures for the third site the stereoactivity increases.     

Semiconductor-metal transition in Ti3O5

Ti₃O₅ shows a first-order phase transition from the monoclinic structure to the pseudobrookite structure at 448°K, at which temperature a magnetic susceptibility anomaly has been reported earlier in the literature. There is an electrical conductivity discontinuity accompanying the phase transition. Incorporation of Fe stabilizes the high-temperature phase of Ti₃O₅; while with 2% Fe the transition temperature and enthalpy change are lowered, with 5% Fe there is no transition. Mössbauer spectra of 2% Fe-doped Ti₃O₅ are similar below and above the transition temperature and show no evidence for magnetic ordering in the low-temperature phase. These results are compared to the VO₂ transition.     

The two components of the crystallographic transition in VO2

Two distinguishable mechanisms of the monoclinic-to-tetragonal transition in VO₂ are identified: an antiferroelectric-to-paraelectric transition at a temperature T_t as well as a change from homopolar to metallic VV bonding at a temperature T_t′. In pure VO₂ at atmospheric pressure, the two transitions occur at the same temperature, T_t′ = T_t = 340°K. However, a T_t′ < T_t may be induced by atomic substitutions; and in the intermediate temperature range the structure is orthorhombic, the antiferroelectric distortions being somewhat different in the absence of homopolar VV bonding. From energy-band considerations, the semiconductor-to-metal transition is to be associated with the transition at T_t; but below T_t′ the semiconducting energy gap should be larger and the charge-carrier mobilities should be smaller. The existence of two transition temperatures in doped VO₂ is distinguished from the claim of two transition temperatures in the Magnéli phases V_nO_2n−1. In this latter case, the appearance of two transitions reflects a two-phase region consisting of two adjoining Magnéli phases.     

Laser magnetic resonance spectrum of the PH2 radical

The PH₂ radical in its ground vibrational and electronic state has been detected by far infrared laser magnetic resonance absorption using the 118.6 μm line of the water vapour laser. The spectrum has been assigned to Zeeman components of the 5₃₂ – 6₄₃ rotational transition.     

High-resolution UV photoelectron spectrum of CO2

The highly-resolved HeI photoelectron spectrum of CO₂ is presented and its vibrational structure studied in detail. In the X? ²Π_g ionic state the v₃ antisymmetric mode is found to be excited in double quanta (v_1-v_2-v₃ = 0. 0. 2) with energy hv₃ = 181 meV. In the C? ²Σ_g⁺ state a single quantum of the same mode is found to be excited (hv₃ = 189 meV) in combination with a v₁ excitation. Vibronic interaction with vibrational levels in the B? ²Σ_u⁺ state of the ion is suggested to promote this (1, 0, 1) excitation. It is established that inelastic scattering processes contribute to the vibrational structure in the C? ²Σ_g⁺ band. The spin-orbit splitting in the X? ²Π_g is determined to be 19±1 meV and 10±2 eV in the ā²Π_u state. Vibronic structure is resolved in the X? ²Π_g band where the Renner-Teller coupling constant is determined to be ? = 0.21±0.02 and the vibrational energy of the v₂ mode as 60±7 meV. In the ā²Π_u state the v₂ energy is found to be hv₂ = 60 meV from the observed hot-band structure.     

Chemical process study on the separation of gadolinium-153

Three routes of chemical processes for a multicurie production of¹⁵³Gd have been established and demonstrated using one gram of Eu₂O₃ as target irradiated under a neutron flux of 5.0·10¹³n/cm²/s for 42 days. Simulated experiments with the synthetic solution containing appropriate amounts of Gd and Eu and the tracers were performed throughout the established chemical process for verifying its feasibility and the effectiveness. The results show that a high specific activity of 100 Ci/g Gd with the desired radionuclide purity of greater than 99.999% of¹⁵³Gd can be obtained. The chemical yield and processing time among the processes were compared.     

Structural aspects of the metal-insulator transition in V4O7

V₄O₇ has a transition with decreasing temperature at 250 K and the structure has been refined at 298 and 200 K. The triclinic structure (A$\text{1}$) consists of rutile-like layers of VO₆ octahedra extending indefinitely in the a-b plane and four octahedra thick along the c-axis. The average VO distances for the four independent V atoms are 1.967, 1.980, 1.969, and 1.984 Å at 298K and 1.948, 1.992. 1.961, and 2.009 Å at 200K. At 200K there is a clear separation into strings of V³⁺ or V⁴⁺ ions running parallel to the pseudorutile c-axis. In addition, all of the 3+ and half of the 4+ sites are paired to form short VV bonds. The remaining V⁴⁺ atom is displaced toward one oxygen so as to balance its electrostatic charge. The distortion at the metal-insulator transitions in V₄O₇, Ti₄O₇, VO₂ + Cr, and NbO₂ are compared.     

The forbidden raman (v2, πu) transition in crystalline CS2

Raman spectra associated with the v₂(π_u) bending vibration of CS₂, which is forbidden for an isolated molecule, are presented The spectra are assigned to combination bands with phonons and show well-resolved critical point structure.