V3 Band Research Articles

Frequency-comb referenced spectroscopy of v4- and v5-excited hot bands in the 1.5 μm spectrum of C2H2

Doppler-free transition frequencies for v4- and v5-excited hot bands have been measured in the v1+v3 band region of the spectrum of acetylene using saturation dip spectroscopy with an extended cavity diode laser referenced to a frequency comb. The frequency accuracy of the measured transitions, as judged from line shape model fits and comparison to known frequencies in the v1+v3 band itself, is between 3 and 22kHz. This is some three orders of magnitude improvement on the accuracy and precision of previous line position estimates that were derived from the analysis of high-resolution Fourier transform infrared absorption spectra. Comparison to transition frequencies computed from constants derived from published Fourier transform infrared spectra shows that some upper rotational energy levels suffer specific perturbations causing energy level shifts of up to several hundred MHz. These perturbations are due to energy levels of the same rotational quantum number derived from nearby vibrational levels that become degenerate at specific energies. Future identification of the perturbing levels will provide accurate relative energies of excited vibrational levels of acetylene in the 7100–7600cm−1 energy region.

Structural, Infrared and Magnetic Properties of Nanosized Ni(x)Zn1-xFe2O4 Powders Synthesized by Sol-Gel Technique.

Ni-Zn ferrites Ni(x)Zn1-xFe2O4 (x = 0.2, 0.4, 0.5, 0.6, 0.8) powders were synthesized by sol-gel technique. Structural, infrared and magnetic properties of samples were investigated. Spinel structural characteristics are shown by XRD spectra and the morphologies observed by atomic force microscopy demonstrate the samples are in nano-range. For all the samples, FTIR spectra exhibit obvious v1 infrared absorbing bands, in the range 500-600 cm-1, corresponding to intrinsic stretching vibrations of the metal ions at the tetrahedral site (Td), Mtetra <--> O. Furthermore, the central position of v1 band is tending to shift to larger wave numbers with the increasing Ni contents in the samples. For the samples Ni(x)Zn1-xFe2O4 (x = 0.2, 0.4), the v2 infrared absorbing bands, in the range 450-385 cm(-1), corresponding to stretching vibrations of the metal ions at the octahedral-metal stretching (Oh), Mocta <--> O, were also observed. However, for samples Ni(x)Zn1-xFe2O4 with higher Ni content (x = 0.5, 0.6, 0.8), the v2 infrared absorbing bands were obscure. The magnetic hysteretic loops at room temperature obtained from vibration samples magnetometer reveal the soft magnetism of the samples. The sample with lowest Ni content, Ni0.2Zn0.8Fe2O4, presents much higher saturation field than the other samples. The coercive field rises with increased Ni content, which is ascribed to the increased magnetocrystalline anisotropy constant with Ni content.

Non‐intrusive in situ detection of methyl chloride in hot gas flows using infrared degenerate four‐wave mixing

We demonstrate the potential of infrared degenerate four‐wave mixing (IR‐DFWM) as a tool for non‐intrusive in situ spatially resolved detection of CH3Cl in reactive hot gas flows especially feasible for applications to biomass combustion and gasification. IR‐DFWM spectra of CH3Cl, by probing ro‐vibrational transitions belonging to the fundamental stretching modes v1 and v4, have been successfully recorded in gas flows diluted with nitrogen at atmospheric pressure and elevated temperatures up to 820 K. In order to identify the spectral lines of CH3Cl, the recorded IR‐DFWM spectra are compared with simulations using molecular parameters extracted from the HITRAN database. The potential interference from water vapor is discussed from measurements of H2O spectrum at 820 K combined with simulations of H2O IR‐DFWM spectrum based on the HITEMP database, and it was found that the QQ6 line of the v1 band is relatively free from water interference at elevated temperatures. At atmospheric pressure, the detection limits for temperatures at 296, 550 and 820 K were estimated to be 2.1, 3.1 and 6.2 (×1015 molecules/cm3), respectively, by scanning the QQ6 line of the v1 band. These results show the potential of interference free detection of CH3Cl with IR‐DFWM in harsh environments like combustion. Copyright © 2015 John Wiley &amp; Sons, Ltd.

High resolution investigation of the v3 band of trifluoromethyliodide (CF3I)

The high-resolution absorption spectrum of trifluoromethyliodide (CF3I), an alternative gas to chlorofluorocarbons but with potential greenhouse effects, has been recorded at 0.001cm−1 resolution in the 200–350cm−1 region with the Bruker IFS125HR Fourier transform spectrometer at synchrotron SOLEIL. Due to the spectral congestion and the presence of numerous hot bands, the spectra have been recorded at the AILES Beamline facility at SOLEIL either at room temperature using a 150m optical path length cell or at 163K using the new LISA-SOLEIL cryogenic cell and at the Australian synchrotron using a flow cooling cell. This enables a detailed analysis of the v3 band at 286.29712(3)cm−1 of CF3I. The results of previous microwave measurements in the v3=1 and v6=1 vibrational states (Walters and Whiffen, 1983; Wahi, 1987) were combined with those of the present infrared analysis of the v3 band to obtain an improved set of parameters for the v3=1 (C–I stretching) and v6=1 (I–C–F bending) interacting vibrational states accounting for the Coriolis resonance coupling the v3=1 energy levels with those of the dark v6=1 state (located at ∼261.5 or at ∼267.6cm−1). Finally, a first investigation of the 2v3−v3 hot band is also performed.

Temperature dependence of air- and N2-broadening coefficients in the v3 band of 13CH4

By using a mid-infrared tunable diode laser and a home-made cooling cell, the N2- and air-broadening coefficients of 13CH4 have been measured at room and low temperatures around 3.38 μm. Four transitions are studied for the 13CH4 diluted with nitrogen and air at temperatures 296, 252, 213, and 173 K. Measurements at low temperatures allow the determination of the temperature dependent parameter of the collisional broadening coefficients. The line parameters are obtained by fitting the experimental profile to the Voigt line shape. The N2- and air-broadening coefficients increase with the drop of the temperature. The collisional broadening coefficients of N2 are always larger than those of air at the same temperature. These data support the remote sensing of the Earth and outer planet atmospheres. According to our knowledge, the line parameters are reported experimentally for the first time.

Preparation, characterization and magnetization of nano and bulk Ni0.5Co0.5−2xLixFe2+xO4 samples

Nanoparticle samples of Ni0.5Co0.5−2xLixFe2+xO4 (x=0.05–0.25) have been prepared by using citrate precursor method. The powders have been divided equally into two groups; one group has been sintered at 600°C for 2h to keep the size of the particles at the nano scale. The other group has been sintered at 1115°C for the same duration to prompt the growth of the particles to the bulk size. The effect of increasing Li1+ and Fe3+ ions on the expense of Co2+ ions onmicrostructure andsome magnetic properties has been studied for the two groups. For that purpose, X-ray diffraction XRD, transmission electron microscopy TEM, Fourier transform infrared FTIR spectroscopy and vibrating sample magnetometer VSM have been used to investigate the samples. Moreover, the effect of varying the pH of the solution during the preparation procedure on different properties has been investigated for one composition; that is, for the sample of x=0.05. The XRD analysis has confirmed the formation of the required samples, while TEM images have been used to check up the average size of the particles of two selected samples only. FTIR spectra have revealed the presence of two prominent absorption bands v1 and v2 around 600cm−1 and 400cm−1 which are usually attributed to the tetrahedral and octahedral complexes in the spinel lattice, respectively. The magnetic measurements may be explained on the basis of a suggested cation distribution although they may be slightly affected by many other factors.

Single and double resonance spectroscopy of methanol embedded in superfluid helium nanodroplets.

Methanol is one of the simplest molecules that undergo torsional oscillations, and so it has been extensively studied in the gas phase by various spectroscopic techniques. At 300 K, a large number of rotational, torsional, and vibrational energy levels is populated, and this makes for a rather complicated spectrum, which is still not fully understood. It is expected that in going from 300 K to 0.4 K (the temperature of helium nanodroplets) the population distribution of methanol will mainly collapse into two states; the JK = 00 state for the A1 nuclear spin symmetry species (with ICH3 = 3/2), and the JK = 1-1 state for the E species (ICH3 = 1/2). This results in a simplified spectrum that consists of narrow a-type (ΔK = 0) lines and broader b- and c-type (ΔK = ±1) lines. We have recorded the rotovibrational spectrum of CH3OH in the OH stretching, CH3 stretching and bending, CH3 rocking, and CO stretching regions, and have firmly assigned five bands (v1, v2, v3, v7, and v8), and tentatively assigned five others (v9, 2v4, v4 + v10, 2v10, and v4 + v5). To our knowledge, the transitions we have assigned within the v4 + v10, 2v10, and v4 + v5 bands have not yet been assigned in the gas phase, and we hope that considering the very small "matrix" shift in helium nanodroplets (<1 cm(-1) for most subband origins of CH3OH), those made here can aid in their gas phase identification. Microwave-infrared double resonance spectroscopy was used to confirm the initially tentative a-type infrared assignments in the OH stretching (v1) band of A1 species methanol, in addition to revealing "warm" b-type lines. From a rotovibrational analysis, the B rotational constant is found to be reduced quite significantly (56%) with respect to the gas phase, and the torsional tunneling splittings are relatively unaffected and are at most reduced by 16%. While most rovibrational peaks are Lorentzian shaped, and those which are significantly perturbed by vibrational coupling in the gas phase are additionally broadened, the narrowest ΔJ = +1 peaks are asymmetric, and a skew-type analysis suggests that the response time of the helium solvent upon excitation is of the order of 1 ns.

Analysis of high-temperature thermoelectric properties of p-type CoSb3 within a two-valence-band and two-conduction-band model

Experimental data on the thermoelectric properties of p-type CoSb3 reported by Caillat et al. [J. Appl. Phys. 80, 4442 (1996)] have been analyzed, assuming not only a pair of the first valence (v1) and the first conduction (c1) bands but also the second valence (v2) and the second conduction (c2) bands. By taking into account the excitation of carriers into the v2 and the c2 bands, the behavior of the Hall coefficient as well as that of the Seebeck coefficient at high temperatures is well explained. By taking into account the nonparabolicity of the v1 band, the temperature dependence of mobility is well explained with assuming scattering due to acoustic phonons, nonpolar and polar optical phonons, and ionized impurities. Furthermore, various material parameters of CoSb3, such as the band-gap energy, effective masses, and deformation potentials, have been deduced from fitting the calculation to the experimental data on the temperature dependences of the Hall coefficient, the mobility, and the Seebeck coefficient. Among them, the band-gap energy and the effective mass of the v1 band have been corrected from the original values estimated by Caillat et al. In addition, it is shown that the experimental data on the hole-concentration dependences of both the room-temperature Seebeck coefficient and the cyclotron mass are well reproduced by the theoretical calculation using the deduced values for the nonparabolic v1 band.

The unique reflection spectra and IR characteristics of golden-color seawater cultured pearl

A comparative study on the natural-color golden seawater cultured pearls and the treated-color golden seawater cultured pearls were carried out by UV-Vis reflectance spectra. Furthermore, the frequency variations of v3, v1 , v2 and v4 bands of the aragonites (a crystal form of calcium carbonate) with the positions of nacreous layer and nucleus in natural or treated-color golden-color seawater cultured pearls were firstly systematically measured. The results showed that: (1) based on the results of UV-Vis reflectance spectra of natural or treated-color golden seawater cultured pearls, interestingly, it was firstly found that the natural-color golden one displays slight varied UV-Vis reflection spectra because of its different surface microstructure located on the outer nacreous layer. Meanwhile, according to the characteristic of UV-Vis reflectance spectra of treated-color golden ones, the treated-color ones were firstly classified to four categories. (2) The frequency of v2 band of aragonite in nacreous layer of natural-color or treated-color golden pearls was greater than the other one from theirs corresponding nucleus, namely A clear blue shift was observed in the former. But the other bands were not altered in the positions of nacreous layer and nucleus, and had the same valves with synthetic aragonites. Additionally, the location of absorption bands of aragonite in nacreous layer of natural or treated-color golden pearls had no frequency shift, which indicates that the behavior of color-treating had no effect on the crystal structure of golden pearls.

CO2 Pressure Shift and Broadening of Water Lines Near 790 nm

Carbon dioxide pressure-broadened ro-vibrational transitions belonging to the v2+3v3 band of H216O have been measured with a sensitive cavity ring-down spectrometer. Water vapor of relatively low pressures (&amp;lt;0.5 Torr) was used to limit the self-collisions among water molecules. After the calibration using the precise atomic transitions of Rb and a thermostabilized Fabry-Pérot interferometer, 10−5 cm−1 frequency accuracy has been achieved. Line parameters are derived from least-squares fitting of the spectra using the “soft” collision model. The retrieved line parameters can be applied in the study of water absorption in the CO2-rich atmospheres of planets like Venus and Mars.

Theory of relaxation parameters of the spectrum shape in the impact approximation−II: Simplifications, application for qQ(J,K) doublets in the v1 band of NH3 self-broadening

In the first part of this paper the general theory of relaxation parameters of the spectrum shape in the impact approximation was presented. Here we describe some simplifications, discuss the isolated line approximation and compare our results with the other methods of a spectral line half-width and center shift calculation. As an example, illustrative calculations of the qQ(J,K) doublets in the v1 band of NH3 self-broadening have been performed and the results are compared with the experiment.

The ro-vibrational analysis of the v4 fundamental band of CF3Br from jet-cooled diode laser and FTIR spectra in the 8.3-μm region

The v4 fundamental band of CF379Br and CF381Br, present in natural isotopic abundance, was investigated in the 8.3-μm region by high-resolution infrared spectroscopic techniques. Tuneable diode laser spectra were recorded in the ranges 1202.5–1205.0 cm−1, 1208.0–1210.1 cm−1 and 1212.5–1214.5 cm−1. The tuneable diode laser spectra were obtained at the reduced temperature of 200 K and in a free-jet expansion. The latter technique was used to reduce spectral congestion, achieving a rotational temperature of about 50 K, with a resolution up to 0.0008 cm−1. A Fourier transform infrared spectrum covering the entire spectral region of the v4 band, between 1190 and 1220 cm−1, was recorded at 298 K with a resolution of 0.004 cm−1. The experimental wavenumbers from the different spectroscopic techniques were combined to accomplish the complete ro-vibrational analysis of v4. In total, 4651 transitions were assigned to CF379Br, 4047 to CF381Br, with J″max = K″max =80; of these, 3171 for CF379Br and 2755 for CF381Br are from diode laser measurements. The data of each isotopologue were analysed using the model Hamiltonian for a degenerate vibrational state of a molecule of C3v symmetry. The v4 band of both the isotopologues resulted essentially unperturbed, but the Δl = Δk = ±2 l-resonance was found to be active within the v4 = 1 state. Precise values of the vibrational energy and of the ro-vibrational parameters of v4 = 1 for CF379Br and CF381Br were obtained. The bromine isotopic splitting amounts to 6.9 × 10−3 cm−1. In addition, the equilibrium geometry and the harmonic force field were calculated ab initio using the large-size basis set def2-QZVP in conjunction to the PBE0 functional.

Observation of enhanced carrier transport properties of Si ⟨100⟩-oriented whiskers under uniaxial strains

In this study, enhancements of the carrier transport properties of p-type ⟨100⟩-oriented Si whiskers are observed under uniaxial tensile and compressive strains. It has been found that over 400% enhancement of electrical conductivity is achieved under a 2% tensile strain, while a 2% compressive strain can only cause ∼80% conductivity enhancement. The enhancements are mainly attributed to the breaking of the degeneracy of the v2 and v1 valence bands induced a reduction of the hole effective mass. This study provides an important insight of how the carrier mobility variation caused by the strain impact on their transport properties.

A Neural Network Algorithm to Detect Sulphur Dioxide Using IASI Measurements

The remote sensing of volcanic sulphur dioxide (SO2) is important because it is used as a proxy for volcanic ash, which is dangerous to aviation and is generally more difficult to discriminate. This paper presents an Artificial Neural Network (ANN) algorithm that recognizes volcanic SO2 in the atmosphere using hyperspectral remotely sensed data from the IASI instrument aboard the Metop-A satellite. The importance of this approach lies in exploiting all thermal infrared spectral information of IASI and its application to near real-time volcanic monitoring in a fast manner. In this paper, the ANN algorithm is demonstrated on data of the Eyjafjallajokull volcanic eruption (Iceland) during the months of April and May 2010, and on the Grímsvotn eruption occurring during May 2011. The algorithm consists of a two output neural network classifier trained with a time series consisting of some hyperspectral eruption datasets collected during 14 April to 14 May 2010 and a few from 22 to 26 May 2011. The inputs were all channels (441) in the IASI v3 band and the target outputs (truth) were the corresponding retrievals of SO2 amount obtained with an optimal estimation method. The validation results for the Eyjafjallajokull independent data-sets had an overall accuracy of 100% and no commission errors, therefore demonstrating the feasibility of estimating the presence of SO2 using a neural network approach also a in cloudy sky conditions. Although the validation of the neural network classifier on datasets from the Grímsvotn eruption had no commission errors, the overall accuracies were lower due to the presence of omission errors. Statistical analysis revealed that those false negatives lie near the detection threshold for discriminating pixels affected by SO2. This demonstrated that the accuracy in classification is strictly related to the sensitivity of the model. The lower accuracy obtained in detecting SO2 for Grímsvotn validation dates might also be caused by less statistical knowledge of such an eruption during the training phase.

Infrared spectra and tunneling dynamics of the N2–D2O and OC–D2O complexes in the v2 bend region of D2O

The rovibrational spectra of the N2-D2O and OC-D2O complexes in the v2 bend region of D2O have been measured in a supersonic slit jet expansion using a rapid-scan tunable diode laser spectrometer. Both a-type and b-type transitions were observed for these two complexes. All transitions are doubled, due to the heavy water tunneling within the complexes. Assuming the tunneling splittings are the same in K(a) = 0 and K(a) = 1, the band origins, all three rotational and several distortion constants of each tunneling state were determined for N2-D2O in the ground and excited vibrational states, and for OC-D2O in the excited vibrational state, respectively. The averaged band origin of OC-D2O is blueshifted by 2.241 cm(-1) from that of the v2 band of the D2O monomer, compared with 1.247 cm(-1) for N2-D2O. The tunneling splitting of N2-D2O in the ground state is 0.16359(28) cm(-1), which is about five times that of OC-D2O. The tunneling splittings decrease by about 26% for N2-D2O and 23% for OC-D2O, respectively, upon excitation of the D2O bending vibration, indicating an increase of the tunneling barrier in the excited vibrational state. The tunneling splittings are found to have a strong dependence on intramolecular vibrational excitation as well as a weak dependence on quantum number K(a).

Rovibrational spectroscopy of formaldehyde in helium nanodroplets

Formaldehyde has been characterized in superfluid helium nanodroplets in the region of the symmetric (ν1) and antisymmetric (ν5) stretching bands. The band origins are blue shifted, consistent with a decrease in the dipole moment and polarizability in going from the ground to excited vibrational states, and the lines within each band are homogeneously broadened, with vibrational lifetimes of 26 and 6.2ps for assigned transitions in the v1 and v5 bands, respectively. The A, B, and C constants are renormalized to 79%, 65%, and 49% of their gas phase values, corresponding to moments of inertia of helium, IHe, of 0.488, 6.88, and 15.3amuÅ2, about the inertial a-, b-, and c-axes, respectively. While partial breakdown of the adiabatic approximation is expected for rotations about the b- and c-axes, the small value of IHe about the a-axis is indicative of near complete breakdown. The larger value of IHe about the c-axis in comparison to the b-axis is attributed to the greater anisotropy of the interaction potential in the plane of H2CO [M.D. Wheeler, A.M. Ellis, Chem. Phys. Lett. 374 (2003) 392].

Infrared spectroscopic characterization of carbonated apatite: A combined experimental and computational study

A combined experimental and computational approach was employed to investigate the feasibility and effectiveness of characterizing carbonated apatite (CAp) by infrared (IR) spectroscopy. First, an experimental comparative study was conducted to identify characteristic IR vibrational bands of carbonate substitution in the apatite lattice. The IR spectra of pure hydroxyapatite (HA), carbonate adsorbed on the HA surface, a physical mixture of HA and sodium carbonate monohydrate, a physical mixture of HA and calcite, synthetic CAps prepared using three methods (precipitation method, hydrothermal route, and solid-gas reaction at high temperature) and biological apatites (human enamel, human cortical bone, and two animal bones) were compared. Then, the IR vibrational bands of carbonate in CAp were calculated with density functional theory. The experimental study identified characteristic IR bands of carbonate that cannot be generated from surface adsorption or physical mixtures and the results show that the bands at ∼880, 1413, and 1450 cm(-1) should not be used as characteristic bands of CAp since they could result from carbonate adsorbed on the apatite crystals surface or present as a separate phase. The combined experimental and computational study reveals that the carbonate v3 bands at ∼1546 and 1465 cm(-1) are, respectively, the IR signature bands for type A CAp and type B CAp.

IMPROVED DETERMINATION OF THE 1 0 -0 0 ROTATIONAL FREQUENCY OF NH 3 D + FROM THE HIGH-RESOLUTION SPECTRUM OF THE ν 4 INFRARED BAND

The high resolution spectrum of the v4 band of NH3D+ has been measured by difference frequency IR laser spectroscopy in a multipass hollow cathode discharge cell. From the set of molecular constants obtained from the analysis of the spectrum, a value of 262817(6) MHz (3sigma) has been derived for the frequency of the 1(0)-0(0) rotational transition. This value supports the assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy observations in Orion-IRc2 and the cold prestellar core B1-bS.

The ethyl radical in superfluid helium nanodroplets: Rovibrational spectroscopy and ab initio computations

The ethyl radical has been isolated and spectroscopically characterized in (4)He nanodroplets. The band origins of the five CH stretch fundamentals are shifted by < 2 cm(-1) from those reported for the gas phase species [S. Davis, D. Uy, and D. J. Nesbitt, J. Chem. Phys. 112, 1823 (2000); T. Häber, A. C. Blair, D. J. Nesbitt, and M. D. Schuder, J. Chem. Phys. 124, 054316 (2006)]. The symmetric CH2 stretching band (v1) is rotationally resolved, revealing nuclear spin statistical weights predicted by G12 permutation-inversion group theory. A permanent electric dipole moment of 0.28 (2) D is obtained via the Stark spectrum of the v1 band. The four other CH stretch fundamental bands are significantly broadened in He droplets and lack rotational fine structure. This broadening is attributed to symmetry dependent vibration-to-vibration relaxation facilitated by the He droplet environment. In addition to the five fundamentals, three a1' overtone∕combination bands are observed, and each of these have resolved rotational substructure. These are assigned to the 2v12, v4 + v6, and 2v6 bands through comparisons to anharmonic frequency computations at the CCSD(T)∕cc-pVTZ level of theory.

In-situ high-pressure behaviors of double-perovskite Sr2ZnTeO6

Structural and spectroscopic properties of Sr2ZnTeO6 (SZTO) were investigated by angle-dispersive synchrotron X-ray powder diffraction and Raman spectroscopy in a diamond anvil cell up to 31 GPa at room temperature. Although SZTO remained stable up to the highest pressure, the different pressure coefficients of the normalized axial compressibility were obtained as βab = 8.16 × 10−3 GPa−1 and βc = 7.61 × 10−3 GPa−1. The bulk modulus B0 was determined to be 190(1) GPa by fitting the pressure-volume data using the Birch-Murnaghan equation of state. All the observed Raman modes exhibited a broadening effect under high pressure. The vibrational band v1 around 765 cm−1, which is associated with the Te—O stretching mode in the basal plane of the TeO6 octahedron had the largest pressure coefficient, and the Grüneisen parameters for all the observed phonon modes were also calculated and presented. These parameters could be used to measure the amount of uniaxial or biaxial strain, providing a fundamental tool for monitoring the magnitude of the shift of phonon frequencies with strains.