Absorption spectrum of the (CF4) dimer in liquid argon solution

The concentration dependence of the shape of absorption bands in the spectrum of CF₄ in liquid argon is studied in the concentration range (0.01–17)×10^?3 molar fractions at 93 K. In all spectral regions related to ν₃, the shape of the spectral function is determined, along with the Fermi resonance 〈ν_i,ν₃+1,ν₄|≈〈νi,ν₃,ν ₄+2|, by the resonance dipole-dipole interaction. In the spectral region of the Fermi doublet ν ₁+ν₃≈ ν₁+2ν₄, the spectrum of the contact (CF₄)₂ dimer is identified. Agreement between this spectrum and the calculated spectrum is achieved by simultaneously taking intramolecular and intermolecular resonances into account. The distance R _C-C in the dimer is 4.85(15) Å. The calculations of the spectra of (¹²CF₄)₂ and (¹³CF₄?¹²CF₄) dimers with this value of R _C-C in the region ν ₃≈2ν₄ agree with the experiment.     

Effect of WO3 on EPR, structure and electrical conductivity of vanadyl doped WO3·M2O·B2O3 (M=Li, Na) glasses

Glasses with composition xWO₃·(30−x)M₂O·70B₂O₃ (M=Li, Na; 0≤x≤15) doped with 2 mol% V₂O₅ have been prepared using the melt-quench technique. The electron paramagnetic resonance spectra have been recorded in X-band (ν≈9.14 GHz) at room temperature (RT). The spin Hamiltonian parameters, dipolar hyperfine coupling parameter and Fermi contact interaction parameter have been calculated. It is observed that the resultant resonance spectra contain hyperfine structures (hfs) only due to V⁴⁺ ions, which exist as VO²⁺ ions in octahedral coordination with a tetragonal compression in the present glass system. The tetragonality increases with WO₃:M₂O ratio and also there is an expansion of 3d_xy orbit of unpaired electron in the vanadium ion. The study of IR transmission spectra over a range 400-4000 cm⁻¹ depicts the presence of WO₆ group. The DC conductivity (σ) has been measured in the temperature range 423-623 K and is found to be predominantly ionic.     

Palladium atoms and its dimers adsorbed on graphene: First-principles study

In this work we have studied the stabilty, electronic and magnetic properties of Pd adatoms and dimers adsorbed on graphene system using first-principles calculations. The adsorption energies for Pd adatom and its dimer have been found to range from −0.986 to −1.135 eV and −0.165 to −1.101 eV, respectively, which signify stable configuration and future utilization of this system in catalysis. A shift but no separation of π and π^? bands at the Dirac point has been observed in case of Pd dimer adsorption in perpendicular configuration, which can be accounted for the breaking of symmetry of the graphene structure due to adsorption. 64-68% spin polarization P(E_F) and 1.944-1.990 μ_B magnetic moment have been observed for Pd dimers adsorbed on graphene in perpendicular configuration for different sites. The unequal values of partial density of states for 4d and 5s orbitals of Pd dimers at Fermi level have been found to be responsible for the generation of high spin polarization.     

Condensation and desorption of nickel tetra-carbonyl on Cu(1 1 0)

The condensation and desorption of nickel tetra-carbonyl (Ni(CO)₄) on Cu(1 1 0) has been studied by thermal desorption spectroscopy. A quite unusual evolution of the desorption spectra is observed. First a desorption peak appears at around 140 K, which disappears with increasing coverage and merges into a clearly separated new desorption peak at around 150 K. This transformation takes place at a coverage of about 10% of a monolayer. It is suggested that the low temperature peak is due to desorption of monomers. With increasing coverage nucleation and growth of multilayer islands starts, from which the desorption energy is higher due to the higher coordination of the carbonyl molecules, compared to that of the monomers. Evaluation of the multilayer desorption spectra yields a desorption energy of 57.9 kJ/mol (0.60 eV) and an unusually high frequency factor of 1.6 × 10¹⁹ s⁻¹.     

The chemistry of C2 perfluoroalkyl iodide on the Cu(1 1 1) single crystal surface

The thermal chemistry of perfluoroethyl iodide (C₂F₅I) adsorbed on Cu(1 1 1) has been investigated by temperature-programmed reaction/desorption (TPR/D), reflection-absorption infrared spectroscopy (RAIRS), and X-ray photoelectron spectroscopy (XPS). I 4d and F 1s XPS spectra show that dissociative adsorption of C₂F₅I to form the surface-bound perfluroethyl (Cu-C₂F₅) moieties occurs at very low temperature (T < 90 K), while the C-F bond cleavage in adsorbed perfluroethyl (Cu-C₂F₅) begins at ca. 300 K. XPS and TPR/D studies further reveal that the reactions of ^βCF₃^αCF_2(ad) on Cu(1 1 1) are strongly dependent on the surface coverage. At high coverages (?0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) evolves, via α-F elimination, into the surface-bound tetrafluoroethylidene moieties (CuCF-CF₃) followed by a dimerization step to form octafluoro-2-butene (CF₃CFCFCF₃) at 315 K as gas product. The surface-bound (Cu-C₂F₅) decomposes preferentially, at low coverages (?0.04 L), via consecutive α-F abstraction to afford intermediate, trifluoroethylidyne (CuCCF₃), resulting in the final coupling reaction to yield hexafluoro-2-butyne (CF₃CCCF₃) at 425 K. However, at middle coverages (ca. 0.08-0.16 L exposure), the adsorbed perfluroethyl (Cu-C₂F₅) first experiences an α-F elimination and then prefers to loss the second F from β position to yield the intermediate of Cu-CF₂-CFCu (μ-η,η-perfluorovinyl), which may further evolve into hexafluorocyclobutene (CF₂CFCFCF₂) at 350 K through cyclodimerization reaction. Our results have also shown that the surface reactions to yield the products, CF₃CFCFCF₃ and CF₃CCCF₃, obey first-order kinetics, whereas the formation of CF₂CFCFCF₂ follows second-order kinetics.     

Influence of gadolinium concentration on the EMR spectrum of Gd in zircon

Electron magnetic resonance (EMR) spectra of gadolinium-doped zircon (ZrSiO₄) powders have been studied at room temperature for gadolinium concentrations between 0.20 and 1.0 mol%. The results suggest that Gd³⁺ ions occupy substitutional sites in the zircon lattice, that the electron magnetic resonance linewidth increases with increasing gadolinium concentration and that the range of the exchange interaction between Gd³⁺ ions is about 1.17 nm, larger than that of the same ion in other host lattices, such as ceria (CeO₂), strontium oxide (SrO) and calcium oxide (CaO). The fact that the electron magnetic resonance linewidth of the Gd³⁺ ion in polycrystalline zircon increases, regularly and predictably, with Gd concentration, shows that the Gd³⁺ ion can be used as a probe to study, rapidly and non-destructively, the crystallinity and degradation of ZrSiO₄.     

FTIR spectroscopy and estimation of the global warming potential of CF3Br and C2F4

High-resolution (0.03 cm⁻¹) absolute infrared photoabsorption cross sections of bromotrifluoromethane (CF₃Br) and tetrafluoroethylene (C₂F₄) have been measured using Fourier-transformed infrared (FTIR) spectroscopy at temperatures between 213 and 296 K. The measured cross sections were subsequently used to estimate the radiative forcings and the global warming potentials of these two species.     

The pressure effect on the photoluminescence and Raman spectra of Nd(DBM)3·Phen

Photoluminescence and Raman spectra of rare earth complex Nd(DBM)₃·Phen (DBM, dibenzoylmethane; Phen, 1,10-phenanthroline) are measured at high pressures. A new Raman band appearing at 1070 cm⁻¹ indicates a second-order phase transition around 5.0 GPa. Although the crystal lattice is destroyed for pressures higher than 7.1 GPa, photoluminescence spectra show that the emission intensity of Nd³⁺ is enhanced dramatically with the pressure increasing up to 9.9 GPa, which is attributed to an efficient intramolecular energy transfer from the ligand to Nd³⁺. By analyzing the energy of the ground and excited states at 9.9 GPa, the ⁴H_11/2 energy level is considered as the main resonance energy level that efficiently accepts the transferred energy from the ligand.     

Spectral studies on Cr ions doped in sodium-lead borophosphate glasses

Electron paramagnetic resonance (EPR), optical absorption and emission spectra of Cr³⁺ ions doped in (30−x) (NaPO₃)₆+30PbO+40B₂O₃+xCr₂O₃ (x=0.5, 2.0, 3.0, 4.0 and 5.0 mol%) glasses have been studied. The EPR spectra exhibit resonance signals with effective g values at g≈4.55 and g≈1.97. The EPR spectra of x=3.0 mol% of Cr₂O₃ in sodium-lead borophosphate glass sample were studied at various temperatures (295-123 K). The intensity of the resonance signals increases with decrease in temperature. The optical absorption spectrum exhibits four bands characteristic of Cr³⁺ ions in octahedral symmetry. From the analysis of the bands, the crystal-field parameter Dq and the Racah interelectronic repulsion parameters B and C have been evaluated. The emission spectrum exhibit one broad band characteristic of Cr³⁺ ions in octahedral symmetry. This band has been assigned to the transition ⁴T_2g (F)→⁴A_2g (F). Correlating EPR and optical data, the molecular bonding coefficient (α) has been evaluated.     

Spectral performance and intensive green upconversion luminescence in Er/Yb-codoped NaY(WO4)2 crystal

Using Czochralski (CZ) pulling method, an Er³⁺/Yb³⁺-codoped NaY(WO₄)₂ crystal was prepared. Absorption spectra, emission spectra and excitation spectra of this crystal were measured at room temperature. Some optical parameters, such as intensity parameters, spontaneous emission probabilities and lifetimes, were calculated from absorption spectra with Judd-Ofelt (J-O) theory. Upconversion luminescence excited by a 970 nm diode laser was studied. In this crystal, green upconversion luminescence is particularly intensive. Energy transfer mechanisms that play an important role in upconversion processes were analyzed. Two cross-relaxation processes: ⁴G_11/2 + ⁴I_9/2 → ²H_11/2 (or ⁴S_3/2) + ²H_11/2 (or ⁴S_3/2), and ⁴G_11/2 + ⁴I_15/2 → ²H_11/2 (or ⁴S_3/2) + ²I_13/2, which contribute to the intensive green luminescence under 378 nm excitation, were put forward. Background energy transfer ⁴G_11/2(Er³⁺) + ²F_7/2(Yb³⁺) → ⁴F_9/2(Er³⁺) + ²F_5/2(Yb³⁺) was also demonstrated.     

Optical and EPR study of BaY2F8 single crystals doped with Yb

Optical and electron paramagnetic resonance study have been carried out on BaY₂F₈ single crystals doped with Yb ions at 0.5 and 10 mol%. The crystals have been obtained using the Czochralski method modified for fluoride crystal growth. Optical transmission measurements in the range of 190-3200 nm and photoluminescence measurements were carried out at room temperature. Absorption spectra of BaY₂F₈ single crystals doped with Yb due to the ²F_7/2→²F_5/2 transitions have been observed in the 930-980 nm range. To analyze the possible presence of Yb²⁺ ions in the investigated crystals, irradiation with γ-quanta with a dose of 10⁵ Gy have been performed. The observed photoluminescence bands show usual emission in IR and other one in VIS, being an effect of cooperative emission of Yb³⁺ ions and energy up-conversion transitions of photons from IR to UV-vis(visible) due to hoping process between energy levels of paired Yb³⁺ and Er³⁺, where Er³⁺ ions are unintentional dopants. The EPR spectra of BaY₂F₈:Yb 10 mol% consist of many overlapping lines. They have been analyzed in terms of spin monomers, pairs, and clusters. The angular dependence of the resonance lines positions have been studied also to find the location of coupled ytterbium ions in the crystal structure.     

Rovibrational spectroscopy of the Fermi-interacting ν4 = 1 and ν3 = ν6 = 1 levels of DCF3

The high-resolution infrared spectrum of deuterated fluoroform (DCF₃) was studied in the 700 and 1200 cm⁻¹ regions, with the aim of assigning and analyzing the ν₄ CF₃ asymmetric stretching vibration. The Fermi-type anharmonic coupling between the ν₄ = 1 and ν₃ = ν₆ = 1 rovibrational levels, already mentioned in an early work of Ruoff et al. [Spectrochimica Acta Part A 31A (1975) 1099-1100], was studied here for the first time under high resolution. Assignments in the ν₃ + ν₆/ν₄ band system were confirmed and extended by the identification of the ν₃ + ν₆ − ν₆ and ν₄-ν₆ bands in the 700 cm⁻¹ region, the latter being enhanced near the Fermi crossings of the studied levels. Data from both the hot and difference bands were included in the analysis. The close separation of the studied vibrational levels of about 14.8 cm⁻¹ produces a large variety of resonance crossings which involve levels with . Besides the Fermi () and Coriolis () resonances, they were accounted for by inclusion of additional higher-order ( and ) interaction terms between the vibrational states. The least-squares fit of more that 16,000 vibration-rotation transitions provides a quantitative reproduction of data in all bands.     

High-resolution infrared spectra of NCCN and NCCN

High-resolution spectra of ¹⁵N¹²C¹²C¹⁵N and ¹⁴N¹³C¹³C¹⁴N have been measured and analyzed from 200 to 3600 cm⁻¹. All the vibrational levels below 900 cm⁻¹ have been observed and characterized. The Fermi resonance between ν₂ and 2ν₄ has been studied and the resonance constant has been determined for several cases. Several Σ⁻ states have been directly observed for the first time for each isotopomer, the (0001111)0f, (0011111)0f, and (0002222)0f states. The pattern of the energy levels for clusters of l-type resonance coupled levels, such as 0001131,3, has been determined for cyanogen for the first time. Among other things this involved the determination of the vibrational l-type resonance constant, r₄₅. Many of the power series constants, α_i and x_ij, and higher order constants have been determined.     

The 4d-4f dipole resonance of the Pr atom in an endohedral metallofullerene, Pr@C82

The photoion yield spectra of an endohedral metallofullerene Pr@C₈₂ were measured in the photon energy range of 100-150 eV by using time-of-flight mass spectrometry. Parent ions Pr@C₈₂⁺, Pr@C₈₂²⁺ and Pr@C₈₂³⁺ were observed in the mass spectra. The photoion yield spectra of Pr@C₈₂²⁺ showed a broad peak at 120-140 eV that was assigned to the 4d-4f giant dipole resonance of the encapsulated Pr atoms. Absolute photoabsorption cross sections of Pr@C₈₂ were evaluated from the photoion yield spectra to be 37±12 Mb at 110 eV (off-resonance) and 52±13 Mb at 130 eV (on-resonance). These cross sections of Pr@C₈₂ were compared with the results of Ce@C₈₂, the only metallofullerene whose photoionization properties have ever been studied near the 4d edge of the encapsulated metal atom. The enhancement of photoabsorption due to the giant resonance was found to be similar in Pr@C₈₂ and Ce@C₈₂, but there are marked differences in the peak shapes, which can be explained as due to interference effects between the fullerene cage and the encapsulated metal atoms.     

High resolution infrared spectroscopy of [1.1.1]propellane: The region of the ν9 band

The region of the infrared-active band of the ν₉ CH₂ bending mode [1.1.1]propellane has been recorded at a resolution (0.0025 cm⁻¹) sufficient to distinguish individual rovibrational lines. This region includes the partially overlapping bands ν₉ (e′) = 1459 cm⁻¹, 2ν₁₈ (l = 2, E′) = 1430 cm⁻¹, ν₆ + ν₁₂ (E′) = 1489 cm⁻¹, and ν₄ + ν₁₅ (A₂″) = 1518 cm⁻¹. In addition, the difference band ν₄ − ν₁₅ (A₂″) was observed in the far infrared near 295 cm⁻¹ and analyzed to give good constants for the upper ν₄ levels. The close proximities of the four bands in the ν₉ region suggest that Coriolis and Fermi resonance couplings could be significant and theoretical band parameters obtained from Gaussian ab initio calculations were helpful in guiding the band analyses. The analyses of all four bands were accomplished, based on our earlier report of ground state constants determined from combination differences involving more than 4000 pairs of transitions from five fundamental and four combination bands. This paper presents the analyses and the determination of the upper state constants of all four bands in the region of the ν₉ band. Complications were most evident in the 2ν₁₈ (l = 2, E′) band, which showed significant perturbations due to mixing with the nearby 2ν₁₈ (l = 0, A₁′) and ν₄ + ν₁₂ (E′) levels which are either infrared inactive as transitions from the ground state, or, in the latter case, too weak to observe. These complications are discussed and a comparison of all molecular constants with those available from the ab initio calculations at the anharmonic level is presented.     

Characterization, EPR and luminescence studies of ZnAl2O4:Mn phosphors

ZnAl₂O₄:Mn green light emitting powder phosphors have been prepared by urea combustion technique involving furnace temperatures about 500 °C in a short time (<5 min). The prepared powders were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectrometry and the surface area measurements by a Brunauer-Emmet-Teller (BET) adsorption isotherms. The EPR spectrum exhibits a resonance signal at g≈2.0, which shows a six-line hyperfine structure (hfs). From the EPR spectra the spin-Hamiltonian parameters have been evaluated at room temperature as well as at 110 K. EPR and photoluminescence (PL) studies revealed that manganese ions were present in divalent state and the site symmetry around Mn²⁺ ions is distorted tetrahedral. The spin concentration (N), the paramagnetic susceptibility (χ) and the zero-field splitting parameter (D) have been evaluated and discussed. The green emission at 511 nm in ZnAl₂O₄:Mn phosphor is assigned to a transition from the upper ⁴T₁→⁶A₁ ground state of Mn²⁺ ions.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

Vibrational spectra and force constants of symmetric tops: ν1, ν5, and 2ν5 of CF335Cl and CF337Cl

The gas phase infrared spectra of CF₃³⁵Cl and CF₃³⁷Cl have been recorded in the ν₁ region and 2ν₅ regions with a resolution of 0.09 cm^?1. Additionally the ν₅ fundamental of CF₃Cl, with natural isotopic abundance, has been reinvestigated with a resolution of approximately 0.36 cm^?1. Molecular constants have been evaluated from the observed spectra by means of polynomials and band contour simulation. The possibility of a Fermi resonance between ν₁ and 2ν₅ is discussed.     

Detection and analysis of new bands of O3 by CRDS between 6500 and 7300 cm

The absorption spectrum of the ¹⁶O₃ isotopologue of ozone has been recorded in the 7000-7920 cm⁻¹ region by high sensitivity CW-Cavity Ring Down Spectroscopy. This report is devoted to the analyses of the 7065-7300 cm⁻¹ region dominated by the ν₁ + 2ν₂ + 5ν₃ and ν₁ + 5ν₂ + 3ν₃ A-type bands at 7130.8 and 7286.8 cm⁻¹ respectively. 289 transitions were assigned to the ν₁ + 2ν₂ + 5ν₃ band. The corresponding line positions were modeled with an effective Hamiltonian involving Coriolis resonance interactions between the (1 2 5) upper state and the (4 4 0), (0 2 6) and (6 1 0) dark states, and an anharmonic resonance interaction with the (2 0 5) state. The very strong interaction (up to 50% mixing of the wavefunctions) between the (1 2 5) and (6 1 0) states leads to the observation of two extra lines of the 6ν₁ + ν₂ band due to a resonance intensity transfer. 213 transitions of the ν₁ + 5ν₂ + 3ν₃ band were assigned and modeled taking into account a Coriolis resonance interaction with the (3 6 0) state.We take the opportunity of the present work to report the analysis of the very weak 4ν₂ + 4ν₃ B-type band at 6506.1 cm⁻¹ which was assigned from previously recorded CRDS spectra. 286 transitions were modeled using the effective Hamiltonian approach.The dipole transition moment parameters of the three analyzed bands were determined by a least-squares fit to the measured line intensities. For the three studied band systems, the effective Hamiltonian and transition moment operator parameters were used to generate line lists provided as Supplementary Materials.     

Ultraviolet photoelectron spectroscopy investigation of interface formation in an indium-tin oxide/fluorocarbon/organic semiconductor contact

It has been demonstrated that hole-injection in organic light-emitting devices (OLEDs) can be enhanced by inserting a UV-illuminated fluorocarbon (CF_x) layer between indium-tin oxide (ITO) and organic hole-transporting layer (HTL). In this work, the process of interface formation and electronic properties of the ITO/CF_x/HTL interface were investigated with ultraviolet photoelectron spectroscopy. It was found that UV-illuminated fluorocarbon layer decreases the hole-injection barrier from ITO to α-napthylphenylbiphenyl diamine (NPB). Energy level diagrams deduced from the ultraviolet photoelectron spectroscopy (UPS) spectra show that the hole-injection barrier in ITO/UV-treated CF_x/NPB is the smallest (0.46 eV), compared to that in the ITO/untreated CF_x/NPB (0.60 eV) and the standard ITO/NPB interface (0.68 eV). The improved current density-voltage (I-V) characteristics in the UV-treated CF_x-coated ITO contact are consistent with its smallest barrier height.