IR-active Modes Research Articles

Fullerite with intercalated freon Ch2F2

Fullerite C60 with intercalated CH2F2 (Freon-32) was prepared for the first time. The sample was studied by elemental analysis, X-ray powder diffraction, mass spectrometry, and IR spectroscopy. The composition of the sample was found to be (CH2F2)C60. The sample had a face-centered cubic lattice with the lattice parameter (1.4284 nm) much larger than that of pure fullerite (1.416 nm). The gas released from the sample during heating in a vacuum to 450°C largely consisted of initial Freon (mass spectrometry data); no Freon destruction products were observed at this temperature. The C-F stretching vibration frequency (1058 cm−1) was shifted in (CH2F2)C60 by 30 cm−1 toward lower wave numbers compared with the gas phase. The absorption bands at 1182 and 1428 cm−1 (IR active modes (F1u) of high-symmetry (Ih) C60 molecules) did not change their positions in the intercalate.

Far infrared reflection spectrum and IR-active modes of MgTiO3

A MgTiO3 ceramic sample was synthesized by solid-state reactions and its far infrared (IR) reflection spectrum recorded. The IR-active vibrational modes of MgTiO3 were calculated using first-principle calculations and the modes were represented by linear combinations of the symmetry coordinates. Using the eigenfrequencies obtained by the density functional theory calculations as initial values, we fitted the infrared reflection spectrum using the four-parameter semiquantum (FPSQ) model and the Lorentz three-parameter classical model. The parameters (ΩjTO, ΩjLO, γjTO, γjLO in FPSQ fitting and Ωj, Sj, γj in the three-parameter model fitting) of seven of the eight modes predicted by group theory analysis were obtained. The transverse optical modes (in FPSQ) are assigned as 279cm−1 (Au), 383cm−1 (Au), 472cm−1 (Au), 673cm−1 (Au) and ∼262cm−1 (Eu), 317cm−1 (Eu), 416cm−1 (Eu), 531cm−1 (Eu). The modes Au (279cm−1), Eu (317cm−1), Au (472cm−1), and Eu (531cm−1), which contain larger components of cation vibrations, contribute most to the microwave dielectric constant and dielectric loss.

Phonon vibrational frequencies of all single-wall carbon nanotubes at the Lambda point: Reduced matrix calculations

With a simple method—the reduced matrix method, we simplified the calculation of the phonon vibrational frequencies according to SWNTs structure and their phonon symmetric property and got the dispersion properties of all SWNTs at Γ point in Brillouin zone, whose diameters lie between 0.6 and 2.5 nm. The calculating time is shrunk about 2–4 orders. A series of the dependent relationships between the diameters of SWNTs and the frequencies of Raman and IR active modes are given. Several fine structures including “glazed tile” structures in ω ∼ d figures are found, which might predict a certain macro-quantum phenomenon of the phonons in SWNTs.

Probing Molecular Binding Effect from Zinc Oxide Nanocrystal Doping in Surface-Stabilized Ferroelectric Liquid Crystal with Two-Dimensional Infrared Correlation Technique

Doping liquid crystal (LC) with nanomaterials has been shown to yield some degrees of freedom for tailoring LC properties. This approach can be employed to produce new LC materials with high application potentials by blending instead of synthesizing new mesogenic molecules. In this paper, we show that doping ferroelectric liquid crystal (FLC) with ZnO nanocrystals improves the alignment order of a surface-stabilized FLC (SSFLC) in both steady-state and field-induced reorientation processes. We used the two-dimensional infrared (2D IR) correlation technique to reveal that the ZnO nanocrystals were uniformly dispersed into the FLC medium. The homogeneous dispersion of ZnO nanodots produces stronger correlations among the IR-active molecular normal modes of FLC molecules, which then leads to more concerted reorientation process at the submolecular level. A molecular binding effect originating from a dipolar interaction of the ZnO nanodot with surrounding CO groups of FLC molecules was proposed to illustrate our measured results. We estimated the total energy reduced by the doping to be about 1000 J/m3. The alignment stability gained is similar to that experienced by FLC molecules within 100-nm distance to an alignment surface with a strong anchoring strength of 1 × 10-4 J·m-2.

Self-Assembled Carbon Nanotubes on Gold: Polarization-Modulated Infrared Reflection−Absorption Spectroscopy, High-Resolution X-ray Photoemission Spectroscopy, and Near-Edge X-ray Absorption Fine Structure Spectroscopy Study

Recently we reported noncovalent functionalization of nanotubes in an aqueous medium with ionic liquid-based surfactants, 1-dodecyl-3-methylimidazolium bromide (1) and 1-(12-mercaptododecyl)-3-methylimidazolium bromide (2), resulting in positively charged single-wall carbon nanotube (SWNT)-1,2 composites. Thiolation of SWNTs with 2 provides their self-assembly on gold as well as templating gold nanoparticles on SWNT sidewalls via a covalent -S-Au bond. In this investigation, we studied the electronic structure, intermolecular interactions, and packing within noncovalently thiolated SWNTs and also nanotube alignment in the bulk of SWNT-2 dried droplets and self-assembled submonolayers (SAMs) on gold by high-resolution X-ray photoemission spectroscopy (HRXPS), C K-edge X-ray absorption fine structure (NEXAFS) spectroscopy, and polarization-modulated infrared reflection-absorption spectroscopy (PM-IRRAS). HRXPS data confirmed the noncovalent nature of interactions within the nanocomposite of thiolated nanotubes. In PM-IRRAS spectra of SWNT SAMs on gold, the IR-active vibrational SWNT modes have been observed and identified. According to PM-IRRAS data, the hydrocarbon chains of 2 are oriented with less tilt angle to the bare gold normal in a SAM deposited from an SWNT-2 dispersion than those of 1 deposited from an SWNT-1 dispersion on the mercaptoethanesulfonic acid-primed gold. For both the dried SWNT-2 bulk and the SWNT-2 SAM on gold, the C K-edge NEXAFS spectra revealed the presence of CH-pi interactions between hydrocarbon chains of 2 and the pi electronic nanotube structure due to the highly resolved vibronic fine structure of carbon 1s --> R*/sigma*C-H series of states in the alkyl chain of 2. For the SWNT-2 bulk, the observed splitting and upshift of the SWNT pi* orbitals in the NEXAFS spectrum indicated the presence of pi-pi interactions. In the NEXAFS spectrum of the SWNT-2 SAM on gold, the upshifted values of the photon energy for R*/sigma*C-H transitions indicated close contact of 2 with nanotubes and with a gold surface. The angle-dependent NEXAFS for the SWNT-2 bulk showed that most of the molecules of 2 are aligned along the nanotubes, which are self-organized with orientation parallel to the substrate plane, whereas the NEXAFS for the SWNT-2 SAM revealed a more normal orientation of functionality 2 on gold compared with that in the SWNT-2 bulk.

Josephson spectroscopy of terahertz losses in [100]-tilt YBa2Cu3O7-x bicrystal junctions

Terahertz losses in the [100]-tilt YBa2Cu3O7-x grain-boundary junctions were studied using admittance Josephson spectroscopy. The I-Vcurves of the [100]-tilt YBa2Cu3O7-x junctions, when annealed in atomic oxygen, were described by the resistively shunted junction model (RSJ) with an accuracy of better than 0.5% at the temperature range, where the characteristic voltage IcRn< kT/2e. The losses were shown to increase with the decrease of the oxygen content in the junction and corresponding decrease of junction conductance Rn-1. At low temperatures, where IcRn» kT/2e, the absorption of Josephson radiation by optical phonon modes in YBa2Cu3O7-xwas found to be reflected in the I-V curve of the [100]-tilt junctions. The most prominent structure is situated at the voltages V≌ 9.5 mV, which gives the corresponding Josephson frequency of 4.6 THz in good agreement with the frequency of the strongest IR active optical phonon mode in YBa2Cu3O7-x. Assignment of additional lines in the derived losses is discussed according to available data on lattice dynamic calculations and experimental data for a dynamic conduction Reσ1(f) of YBa2Cu3O7-x. Josephson spectroscopy might be useful for study of low-energy excitations in high-Tc materials.

Band structure and dielectric properties of orthorhombic SrZrO 3

Ab initio density functional theory has been used to study the electronic band structure, k = 0 (zone center) vibrational modes, and dielectric properties of the crystalline high- κ perovskite oxide SrZrO 3. The frequencies of the k = 0 normal modes are computed by the linear response technique and then grouped according to their symmetry. The dielectric intensity of each IR-active mode has been determined. It is found that the calculated orientationally averaged static dielectric constant ε 0 = 21.49 is in good agreement with experiment.

Non-adiabatic [formula omitted], D′, β, γ, δ transitions in the first ion-pair tier of molecular iodine induced by collisions with I 2, N 2 and CO 2

Optical–optical double resonance spectroscopy is used to obtain total rate constants, electronic branching ratios, and vibrational product state distributions for non-adiabatic transitions among the first-tier ion-pair states of the I 2 molecule excited to the E 0 g + , v E = 8, 13, 19; J E ≈ 55 rovibronic levels in collisions with M = I 2, N 2 and CO 2. It is shown that I 2 ( E → M D ) near-resonant transitions are caused by the interaction between the transition dipole moment of I 2(E–D) and the electric quadrupole moment of M. Besides, there are transitions induced by polarization interactions of the collision partners. Wide non-resonant vibrational distributions at the final states correspond to them. The I 2(D and β) state vibrational levels populated in the transitions accompanied by excitation of IR active vibrational mode, CO 2(01 10 ← 000) ν 2e 1u(667 cm −1), are observed. It is shown that rotational excitation of the collision partners can compensate energy mismatch between initial and final rovibrational levels.

Transient 2D IR spectroscopy of ubiquitin unfolding dynamics.

Transient two-dimensional infrared (2D IR) spectroscopy is used as a probe of protein unfolding dynamics in a direct comparison of fast unfolding experiments with molecular dynamics simulations. In the experiments, the unfolding of ubiquitin is initiated by a laser temperature jump, and protein structural evolution from nanoseconds to milliseconds is probed using amide I 2D IR spectroscopy. The temperature jump prepares a subensemble near the unfolding transition state, leading to quasi-barrierless unfolding (the "burst phase") before the millisecond activated unfolding kinetics. The burst phase unfolding of ubiquitin is characterized by a loss of the coupling between vibrations of the beta-sheet, a process that manifests itself in the 2D IR spectrum as a frequency blue-shift and intensity decrease of the diagonal and cross-peaks of the sheet's two IR active modes. As the sheet unfolds, increased fluctuations and solvent exposure of the beta-sheet amide groups are also characterized by increases in homogeneous linewidth. Experimental spectra are compared with 2D IR spectra calculated from the time-evolving structures in a molecular dynamics simulation of ubiquitin unfolding. Unfolding is described as a sequential unfolding of strands in ubiquitin's beta-sheet, using two collective coordinates of the sheet: (i) the native interstrand contacts between adjacent beta-strands I and II and (ii) the remaining beta-strand contacts within the sheet. The methods used illustrate the general principles by which 2D IR spectroscopy can be used for detailed dynamical comparisons of experiment and simulation.

Synthesis and gas phase nitridation of nanocrystalline TiO2

Gas phase nitridation of nc-TiO2 was carried out for obtaining nc-TiN. The nc-TiO2 precursor itself was derived from a Ti(OH)x precipitate formed through hydrolysis of titanium nitrate solution by aqueous ammonia reagent. Calcination of titanium hydroxide at 1000 °C yielded nc-TiO2 powder with an average particle size of ∼5 nm. Both nc-Ti(OH)x as well as nc-TiO2 were separately nitrided in an environment of argon and ammonia for synthesizing nc-TiN. A home-built thermogravimetric analysis-mass spectrometer apparatus was used for the nitridation experiment. The nanocrystalline phases of Ti(OH)x, TiO2 and TiN were characterized by XRD, TEM, IR and XPS techniques. The powders' XRD patterns indicated the formation of nanocrystalline TiN by ammonia bases nitridation of nc-TiO2. These studies also revealed sequential crystallo-chemical transformation of the intermediate precursor. FTIR studies revealed the existence of IR active modes in nc-TiO2 and the formation of a chemically pure TiN phase. The TEM image of TiN powder depicted the formation of nanocrystalline phase. Ti(2p3/2) photoelectron spectra indicated complete conversion of nc-TiO2 to nc-TiN.

IR spectra and vibrational dephasing of the CO stretching mode in W(CO) 6 doped cryogenic matrices

Environment effects on the vibrational dynamics of tungsten hexacarbonyl in cryogenic matrices are investigated with the use of the CLIO infrared free-electron laser by measuring the population relaxation time T 1 in the pump-probe configuration and the dephasing time T 2 in the two-pulse photon-echo arrangement. The probe molecule W(CO) 6 is selected because of its exceptionally large vibrational transition dipole moment on the CO stretching mode. Results in cryogenic matrices are obtained for the first time. In these solids (Ar, N 2, CH 4) in the 6–30 K temperature range, the degeneracy of the T 1u IR-active mode is removed. In all matrices, the T 1 time remains of the same order of magnitude, also as measured in other systems, suggesting that T 1 is only weakly influenced by the nature of the host. The W(CO) 6 absorption band is inhomogeneously broadened and the dephasing time T 2, which is long in the argon host ( T 2 = 2 T 1 = 400 ps) is considerably shortened in the molecular matrices, nitrogen or methane ( T 2 = 40–70 ps at 7 K). Interestingly also, the absorption spectrum of W(CO) 6 in the methane host becomes narrower upon a temperature increase. In these two systems, specific dephasing mechanisms exist while these are absent in the case of argon. They can be correlated to the existence of additional orientational degree of freedom of the host, libration in the case of nitrogen, and nearly free rotation in the case of methane.

Robustness of quantum gates operating on the high frequency modes of MnBr(CO) 5

Quantum gates are optimized for the IR active high frequency modes of MnBr(CO) 5-complexes. We investigate whether the selectivity for quantum gates is conserved for energetically close lying qubits of different symmetry that are nevertheless simultaneously addressable with the same laser pulse. The qubits are encoded in different vibrational normal modes, which are separated only by 50 cm −1. Furthermore the influence of additional non-qubit modes on the efficiency of the quantum gates optimized for the pure qubit system is studied. Potential perturbers are low frequency vibrational modes highly populated at room temperature or vibrational modes that seems predestined to interfere during the gate operation. To prevent translational motion, the possibility of spatial localization is explored by incorporation of the carbonyl complex in the unit cell of a MFI zeolite.

Optical and microstructural properties of p-type SrCu 2O 2: First principles modeling and experimental studies

In this paper, we report first principles calculations and experimental studies of the optical and microstructural properties of both bulk and thin films of SrCu 2O 2. Polycrystalline SrCu 2O 2 films were grown by a conventional Pulsed Laser Deposition method in a flowing oxygen environment on corning glass 7059 and silicon substrates. Several characterization techniques, including X-ray diffraction (XRD), Fourier Transform IR (FTIR), Raman, spectroscopic ellipsometry, reflectance/transmission spectrophotometry and Atomic Force Microscopy have been used for the investigation of the microstructural and vibrational properties of both bulk and thin films of SrCu 2O 2. XRD shows that bulk SrCu 2O 2 is polycrystalline and assumes the pure tetragonal phase of SrCu 2O 2. The vibrational properties of the tetragonal phase of SrCu 2O 2 have been inferred from Raman and FTIR spectroscopies and for the first time both Raman and IR active modes have been assigned. The bulk polycrystalline SrCu 2O 2 optical band gap determined from spectroscopic ellipsometry was 3.34 ± 0.01 eV. XRD results confirmed that pure non-textured polycrystalline phase SrCu 2O 2 thin films with a smooth surface can be grown by PLD at low temperature (300 °C).

IR-active vibrational modes of CdTe and CdSe colloidal quantum dots and CdTe/CdSe core/shell nanoparticles and coupling effects

The frequencies of the vibrational modes of CdTe and CdSe quantum dots and CdTe/CdSe core/shell nanoparticles prepared by the colloid chemistry method are determined using IR transmission and IR reflection spectroscopy. The experimental IR transmission spectrum of CdTe and CdSe nanocrystals exhibits a broad minimum located between the frequencies of the transverse optical (TO) and longitudinal optical (LO) phonons of bulk CdTe and CdSe crystals. The frequencies of the modes for ensembles of CdTe and CdSe quantum dots are considerably shifted toward lower frequencies as compared to those calculated for single quantum dots. This is explained by the dipole-dipole interaction between quantum dots. The frequencies of modes for the structures with core/shell nanoparticles differ little from the calculated frequencies. This suggests a weakening of the interaction in these structures due to the enhancement of dielectric screening.

Structural and electron properties of the highest epoxygenated fullerene C 60O 30, a DFT study

Ab initio Hartree–Fock (HF) and density functional theory (DFT) calculations were carried out to determine the structural and electronic properties of the highest epoxygenated fullerenes C 60O 30. For comparison, other fullerene oxides C 60O 29, C 60O 3, C 60O 2 and C 60O were also studied. The highly symmetrical I h structure of the parent C 60 is reserved in C 60O 30 and C 60O 30 was calculated to be a nonpolar molecule. It was demonstrated that C 60O 30 should be more stable than other C 60 oxides such as C 60O 29, C 60O 3, C 60O 2 and C 60O. Compared with C 60, it is less possible for C 60O 30 to accept or donate electrons from the reduced EAs and enhanced IPs. The IR active modes and harmonic vibrational frequencies of C 60O 30 were also discussed.

Combustion synthesis, characterization and metal–insulator transition studies of nanocrystalline La 1− xCa xMnO 3 (0.0 ≤ x ≤ 0.5)

Nanocrystalline CMR materials La 1− x Ca x MnO 3 (0.0 ≤ x ≤ 0.5) are prepared by a low temperature, self-propagating combustion synthesis. As-formed and heat treated calcium doped lanthanum manganites are crystalline, showing cubic symmetry. However, as-formed cubic LaMnO 3 on calcination at 900 °C for 6 h, transformed into rhombohedral phase. The microstructure and morphology of the compounds show that the particles are nearly spherical in shape and are agglomerated. Differential thermal analysis (DTA) curve reveals a broad exothermic peak around 900 °C, while the thermogravimetric (TG) curve exhibits a gradual weight loss from 650 °C onwards, corresponding to reduction of Mn 4+ to Mn 3+. The surface area of manganites increases from 12.5 to 24 m 2 g −1 with increase in calcium content. Both undoped and doped lanthanum manganites show two IR active vibrational modes at 400 and 600 cm −1, corresponding to bending ( ν b) and stretching modes ( ν s) of the Mn–O–Mn bond, respectively. The metal–insulator transition temperatures ( T M–I) are found to lie in the range 117–235 K for combustion derived samples, which are low compared to those prepared by ceramic route.

Hyper-Raman macro- and micro-spectroscopy in materials: Towards high quality signals and good spatial resolution

We have developed two bright hyper-Rayleigh/hyper-Raman spectrometers that allow the collection of spontaneous signals with high-quality and good spatial resolution. The first macro-spectrometer has been addressed to the study of liquids. The second is a new and original micro-spectrometer which has been designed to study solid and interface media. The micro-hyper-Raman spectrometer opens new fields of investigation since it provides vibrational informations, on IR-active but Raman-inactive modes, at the micrometer scale. Thus, the combination of Raman and hyper-Raman methods accomplishes high spatial resolution vibrational micro-spectroscopy.

Ab-initio calculations of Raman, IR-active vibrational modes in isotopically modified B 12 icosahedral clusters

Computational calculations of Becke's three-parameter hybrid method using the LYP correlation functional (B3LYP) have been performed on (B 12H 12) 2− dodecaborane anions with different boron isotopic compositions. This was done in order to investigate isotopic dependence of vibrational spectral properties of B 12 icosahedra, and for comparison of the optical vibrational properties of the icosahedral molecule with the characteristics of inter- or intra-icosahedral optical phonon vibrational modes in boron-rich crystals.

Far-Infrared Spectroscopy of Small Neutral Silver Clusters

The vibrational spectra of Ag(3) and Ag(4) are recorded in the far-infrared between 100 and 220 cm(-1) using multiple photon dissociation spectroscopy of their complexes with Ar atoms. For Ag(3)-Ar two IR active bands are found at 113 and 183 cm(-1), for Ag(4)-Ar one band at 163 cm(-1) and very weak IR activity at 193 cm(-1) are observed. This, together with recent theoretical studies, allows for a reassignment of the controversial vibrational data reported earlier for the bare Ag(3) cluster. The influence of the number of Ar atoms in the complexes on the frequency of the IR active modes is found to be minor. However, the low-frequency IR-active band of Ag(3) shifts with increasing Ar coverage from 113 cm(-1) for Ag(3)-Ar to about 120 cm(-1) for Ag(3)-Ar(4), the value known for Ag(3) embedded in rare gas matrices.

Pressure-tuning Raman and infrared spectra of N-thiocyanato[tris( o-tolyl)]tin(IV), ( o-CH 3C 6H 4) 3SnNCS

The effect of high external pressures on the Raman and IR spectra of the title compound ( I) has been examined at ambient temperature. A pressure-induced phase transition was observed at 13–16 kbar, which is most likely second-order, resulting from slight rotations of the phenyl rings and/or the CH 3 groups under the influence of pressure. No new peaks were observed in the spectra with increasing pressure indicating that no pressure-induced linkage isomerism or SnNCS⋯Sn bridging took place. The average pressure sensitivity (d ν/dP) of the Raman-active vibrational modes is lower in the low-pressure region (0.23 cm −1/kbar) than in the high-pressure one (0.47 cm −1/kbar). In general, the IR-active modes are less sensitive to increasing pressure than are the Raman-active modes and the average d ν/dP value for the IR-active modes in the low-pressure region is quite similar to that in the high-pressure region, i.e., about 0.23 cm −1/kbar.