N Bands Research Articles

Ro-vibrational analysis of the hot bands of 13C2H4: [formula omitted] and [formula omitted

Two “hot” absorption bands, ν7+ν10-ν10 and ν10+ν12-ν10, of 13C2H4 were recorded for the first time with a Bruker high resolution Fourier transform spectrometer and theoretically analyzed. About 640 and 270 transitions (168 and 136 upper state ro-vibrational energy values) with Jmax.=20,Kamax.=10 and Jmax.=23,Kamax.=9 for the bands ν7+ν10-ν10 and ν10+ν12-ν10, respectively, were assigned. For that purpose strong local resonance interactions with ten other closely located vibrational states were taken into account. A set of 36 varied parameters was obtained from the fit, which reproduces the initial experimental data with the rms deviation of 6.7×10-4cm and which is close to experimental uncertainties.

Study of the high resolution spectrum of 32S16O18O: The ν1 and ν3 bands

The high resolution infrared spectrum of the 32S16O18O molecule was recorded for the first time with a Bruker IFS 120 HR Fourier transform interferometer in the region of 930–1580cm−1 where the bands ν1 and ν3 are located. More than 3000 and about 2400 transitions were assigned in the experimental spectrum with the maximum values of quantum numbers Jmax./Kamax. equal to 58/23 and 68/23 to the bands ν1 and ν3, respectively. The further weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account Coriolis resonance interaction between the vibrational states (100) and (001). The 81 microwave transitions of the states (100) and (001) known from the literature also were taken into account. As the result, a set of 26 fitted parameters was obtained which reproduces the experiment-based 2690 ro-vibrational energy values of the two bands with the drms=1.8×10−4cm−1. Microwave transitions are also reproduced with the accuracy close to experimental uncertainty.

Pressure-induced structural changes in NH4Br.

We report angle dispersive X-ray diffraction (XRD) measurements and Raman spectroscopy on NH4Br up to 70.0 GPa at room temperature. Three thermodynamically stable phases (phases II, IV, and V) are confirmed and a new possible phase (phase VI) of P21/m symmetry is proposed whose structure was established from Rietveld refinement of synchrotron XRD data for the first time. The phase sequence observed in NH4Br is in accordance with phase II → IV → V → VI. Phase V transforms into phase VI at about 57.8 GPa with a huge volume reduction of 30%. Still, the intramolecular distances are analyzed to better understand the nature of structures. The H-H interactions become markedly more important as the N-Br distances are compacted, which is probably the reason of the kink of symmetric stretching band (ν1) at the transition pressure.

Structural phase transformations of as-synthesized Cu-nanoferrites by annealing process

Samples of the as-synthesized CuFe2O4 nanoferrites by co-precipitation route were annealed at different temperatures T. X-ray diffraction, infrared and Mössbauer spectroscopy and vibrating sample magnetometry were used for characterizing the samples. The sample structure phase was transformed from cubic-to-tetragonal-to-cubic as T increases. This transformation was attributed to the tetragonal distortion of Jahn–Teller effect of Cu2+ ions (d9). The crystallite size R, lattice parameters, density, porosity P, strain and stiffness constant showed dependence on annealing temperature T. Seven absorption bands were observed in the IR spectra. The two characteristic bands of spinel ferrites, ν1 and ν2, force constants and Debye temperature showed a decrease against T. The absorption bands ν1 and ν2 proved dependence on bond length; dAO and dBO, and saturation magnetization Ms, respectively. Hyperfine magnetic fields, line widths, area ratio of B- to A-sites, isomer shifts and quadrupole shifts (splitting) were deduced and discussed as functions of T, where the cation distribution were estimated. XRD patterns, Infrared spectra and RT temperature hysteresis loops proved the transformation process. Saturation magnetization showed dependence on T, P and R.

High resolution analysis of 32S18O2 spectra: The ν1 and ν3 interacting bands

Highly accurate, ~(1−2)×10−4cm−1, ro-vibrational spectrum of S18O2 was recorded with Bruker IFS 120 HR Fourier transform interferometer in the region of 1050–1400cm−1 where the bands ν1 and ν3 are located. About 1560 and 1840 transitions were assigned in the experimental spectrum with the maximum values of quantum numbers Jmax./Kamax. equal to 65/22 and 58/16 to the bands ν3 and ν1, respectively. The further weighted fit of experimentally assigned transitions was made with the Hamiltonian model which takes into account Coriolis resonance interaction between the vibrational states (100) and (001). To make the ro-vibrational analysis physically more suitable, the initial values of main spectroscopic parameters have been estimated from the values of corresponding parameters of the S16O2 species on the basis of the results of the Isotopic Substitution theory. Finally, the set of 23 spectroscopic parameters obtained from the fit reproduces values of 1292 initial “experimental” ro-vibrational energy levels (about 3400 transitions assigned in the experimental spectrum) with the drms=0.00015cm−1. Also, the ground state parameters of the S18O2 molecule were improved.

Structural, magnetic, and acidic properties of cobalt ferrite nanoparticles synthesised by wet chemical methods

A detailed investigation on the effect of preparation method on the structural, magnetic, and acidic properties of cobalt ferrite nanoparticles prepared by sol-gel and co-precipitation is presented. Citric acid and ethylene glycol were used as gelling agents, while sodium hydroxide and aqueous ammonia were used as precipitating agents. The resulting ferrites were calcined at 450 ℃ and 750 ℃. Sharper X-ray diffraction (XRD) peaks were observed for the samples calcined at 750 ℃, indicating greater crystallinity of the samples calcined at higher temperature. Average crystallite sizes fell in the ranges of 7.1-21.1 nm and 30.4-42.1 nm for the samples calcined at 450 ℃ and 750 ℃, respectively. The infrared spectra revealed two main absorption bands, the high frequency band ν1 around 600 cm 1 and the low frequency band ν2 around 400 cm 1 arising from stretching vibrations of the oxygen bond with the metal in the tetrahedral (A) and octahedral (B) sites in the spinel lattice. Agglomeration of particles was observed in the scanning electron microscopy (SEM) images. Magnetic parameters of CoFe2O4 nanoparticles greatly depended on calcination temperature and preparation techniques. Ammonia temperature programmed desorption (TPD) measurements indicated that weak acid sites predominate medium strength sites, while the number of strong acid sites is the least. Cumulative acidity decreased for the samples calcined at higher temperature. The results underline the effect of preparation conditions on the morphology, crystallite size, and magnetic properties of nano ferrites.

Precise ro-vibrational analysis of molecular bands forbidden in absorption: The [formula omitted] band of 13C2H4

The high resolution spectra of the 13C2H4 molecule was recorded with a Bruker IFS 120 Fourier transform spectrometer and theoretically analyzed in the 1650−1800cm−1 region of the ν8+ν10 band which is forbidden in absorption. About 1200 experimental transitions with the maximum values of quantum numbers Jmax.=34 and Kamax.=17 were assigned to the ν8+ν10 band. On that basis the 516 high accuracy ro-vibrational energies of the (v8=v10=1) vibrational state, as well as energy levels with J≤2 of the (v4=v8=1) and (v7=v8=1) vibrational states, were determined which then were used as input data in the weighted fit of spectroscopic parameters of the Hamiltonian (strong local resonance interactions of the ν8+ν10 band with the bands ν4+ν8 and ν7+ν8 have been taken into account). A set of 34 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. These parameters reproduce positions of about 1200 experimentally recorded and assigned transitions with the rms error drms=0.00018cm−1 (blended and very weak transitions are not taken into account in that case).

Temperature-dependence thermoelectric power studies of mixed Ni–Cu nano ferrites

Synthesized Ni–Cu nano ferrites with the compositional formula Ni1−xCuxFe2O4 (x=0.0, 0.2, 0.4, 0.5, 0.6, 0.8 and 1.0) were prepared by the citrate-gel auto combustion technique. The prepared samples were characterized using X-ray difractrograms (XRD), Transmission electron microscope (TEM) and Fourier transforms infrared (FTIR). The X-ray difractrograms (XRD) clearly exhibited the existence of single phase cubic spinel structure and the crystallite size was found in the range of 36–58nm. TEM micrographs indicated the nanostructure nature with platelet shape. FTIR absorption spectra revealed the presence of two significant absorption bands ν1 and ν2 around 580cm−1 and 410cm−1 characteristic of spinel ferrite. This confirms the formation of single phase spinel structure with two sub-lattices tetrahedral (A) site and octahedral (B) site. The thermoelectric properties were carried out by the differential method from room temperature to well beyond the transition temperature. The seebeck coefficient is negative for all the compositions showing that these ferrites behave as n-type semiconductors. The transition temperature determined from thermoelectric power studies, it was found that the transition temperature decreases with increase of Cu concentration. The values of the charge carrier concentration and charge carrier mobility have been computed from the observed values of the seebeck coefficient. The temperature variation of the seebeck coefficient and carrier concentration is also discussed. On the basis of these results an explanation for the conduction mechanism in Ni–Cu nano ferrites is suggested.

Nonlinear optical absorption and optical limiting properties of cadmium ferrite

Cadmium ferrite (CdFe2O4) was synthesized by simple combustion method and characterized by structural (XRD, SEM, EDS, and FTIR), magnetic (VSM) and nonlinear optical (Z-Scan) studies. Powder X-ray diffraction confirms the formation of cubic phase of CdFe2O4 with the cell constant a = 8.692 Å and a = 8.698 Å for the samples annealed at 500 °C and 800 °C respectively. The average crystallite size was found to increase with an increase in annealing temperature. In the IR spectra of spinel ferrites, the two major absorption bands ν1 (553.47, 549.61 cm−1) and ν2 (410.75, 424.26 cm−1) corresponds to the vibration of tetrahedral and octahedral sites of CdFe2O4. VSM studies shows that material is antiferromagnetic in nature, when heated at higher temperature. Optical nonlinearity of the samples was studied by open aperture Z-scan technique using Q-switched Nd:YAG (532 nm, 5 ns, 10 Hz) laser. The material possesses reverse saturable absorption and can be ascribed due to two photon absorption process. Also the materials exhibit optical limiting behavior with onset limiting value of 4.45 × 1012 W/m2, 3.59 × 1012 W/m2 for the samples annealed at 500 °C and 800 °C respectively.

Precise ro-vibrational analysis of molecular bands forbidden in absorption: The [formula omitted] band of the 12C2H4 molecule

The highly accurate (experimental accuracy in line positions ∼(1-2)×10-4cm−1) ro-vibrational spectrum of the ν8+ν10 band of the 12C2H4 molecule was recorded for the first time with high resolution Fourier transform spectrometry and analyzed in the region of 1650–1950cm−1 using the Hamiltonian model which takes into account Coriolis resonance interactions between the studied ν8+ν10 band, which is forbidden in absorption, and the bands ν4+ν8 and ν7+ν8. About 1570 transitions belonging to the ν8+ν10 band were assigned in the experimental spectra with the maximum values of quantum numbers Jmax.=35 and Kamax.=18. On that basis, a set of 38 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. They reproduce values of 598 initial “experimental” ro-vibrational energy levels (positions of about 1570 experimentally recorded and assigned transitions) with the rms error drms=0.00045cm−1 (drms=0.00028cm−1 when upper ro-vibrational energies obtained from blended and very weak transitions were deleted from the fit).

The dipole moment surface for hydrogen sulfide H2S

In this work we perform a systematic ab initio study of the dipole moment surface (DMS) of H2S at various levels of theory and of its effect on the intensities of vibration–rotation transitions; H2S intensities are known from the experiment to display anomalies which have so far been difficult to reproduce by theoretical calculations. We use the transition intensities from the HITRAN database of 14 vibrational bands for our comparisons. The intensities of all fundamental bands show strong sensitivity to the ab initio method used for constructing the DMS while hot, overtone and combination bands up to 4000cm−1 do not. The core-correlation and relativistic effects are found to be important for computed line intensities, for instance affecting the most intense fundamental band (ν2) by about 20%. Our recommended DMS, called ALYT2, is based on the CCSD(T)/aug-cc-pV(6+d)Z level of theory supplemented by a core-correlation/relativistic corrective surface obtained at the CCSD[T]/aug-cc-pCV5Z-DK level. The corresponding computed intensities agree significantly better (to within 10%) with experimental data taken directly from original papers. Worse agreement (differences of about 25%) is found for those HITRAN intensities obtained from fitted effective dipole models, suggesting the presence of underlying problems in those fits.

In situ surface-enhanced Raman spectroelectrochemical analysis system with a hemin modified nanostructured gold surface.

An integrated surface-enhanced Raman scattering (SERS) spectroelectrochemical (SEC) analysis system is presented that combines a small volume microfluidic sample chamber (<100 μL) with a compact three-electrode configuration for in situ surface-enhanced Raman spectroelectrochemistry. The SEC system includes a nanostructured Au surface that serves dual roles as the electrochemical working electrode (WE) and SERS substrate, a microfabricated Pt counter electrode (CE), and an external Ag/AgCl reference electrode (RE). The nanostructured Au WE enables highly sensitive in situ SERS spectroscopy through large and reproducible SERS enhancements, which eliminates the need for resonant wavelength matching of the laser excitation source with the electronic absorption of the target molecule. The new SEC analysis system has the merits of wide applicability to target molecules, small sample volume, and a low detection limit. We demonstrate in situ SERS spectroelectrochemistry measurements of the metalloporphyrin hemin showing shifts of the iron oxidation marker band ν4 with the nanostructured Au working electrode under precise potential control.

Effect of Aluminium Doping on Structural and Magnetic Properties of Ni-Zn Ferrite Nanoparticles

Aluminium doped Ni-Zn ferrite nanoparticles of general formula of Ni0.5Zn0.5AlxFe2-xO4 (x = 0.0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0) have been synthesized by sol-gel auto combustion method and characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dis-persive X-ray (EDX), Fourier transform spectroscopy (FTIR) and vibrating sample magneto meter (VSM). XRD studies confirm that all compositions show single phase cubic spinel structure. The crystallite size was calculated using the Debye-Scherrer formula and found in the range of 17 - 52 nm. The lattice parameter “a” is found to decrease with increasing Al3+ content. The SEM images clearly show the crystalline structure and EDX patterns confirm the compositional formation of the synthesized compositions. The results of FTIR analysis indicated that the functional groups of Ni-Zn spinel ferrite were formed during the sol-gel synthesis process. The IR spectra showed two main absorption bands, the high frequency band ν1 around 600 cm-1 and the low frequency band ν2 around 400 cm-1 arising from tetrahedral (A) and octahedral (B) interstitial sites in the spinel lattice. As doping is increased the magnetic behavior is found to decrease and the composition x = 2.0 ferrite appears to be exhibiting superparamagnetism as the coercive field and retentivity are found near zero.

Infrared absorption of gaseous CH2BrOO detected with a step-scan Fourier-transform absorption spectrometer.

CH2BrOO radicals were produced upon irradiation, with an excimer laser at 248 nm, of a flowing mixture of CH2Br2 and O2. A step-scan Fourier-transform spectrometer coupled with a multipass absorption cell was employed to record temporally resolved infrared (IR) absorption spectra of reaction intermediates. Transient absorption with origins at 1276.1, 1088.3, 961.0, and 884.9 cm(-1) are assigned to ν4 (CH2-wagging), ν6 (O-O stretching), ν7 (CH2-rocking mixed with C-O stretching), and ν8 (C-O stretching mixed with CH2-rocking) modes of syn-CH2BrOO, respectively. The assignments were made according to the expected photochemistry and a comparison of observed vibrational wavenumbers, relative IR intensities, and rotational contours with those predicted with the B3LYP/aug-cc-pVTZ method. The rotational contours of ν7 and ν8 indicate that hot bands involving the torsional (ν12) mode are also present, with transitions 7(0)(1)12(v)(v) and 8(0)(1)12(v)(v), v = 1-10. The most intense band (ν4) of anti-CH2BrOO near 1277 cm(-1) might have a small contribution to the observed spectra. Our work provides information for directly probing gaseous CH2BrOO with IR spectroscopy, in either the atmosphere or laboratory experiments.

High resolution ro-vibrational analysis of interacting bands ν4, ν7, ν10, and ν12 of 13C2H4

High accurate, ~1×10−4cm−1, ro-vibrational spectra of the C213H4 molecule in the region of 600–1600cm−1 were recorded with Bruker IFS 120/125 HR Fourier transform interferometers and analyzed in the Hamiltonian model which takes into account Coriolis resonance interactions between all four bands. More than 660, 3870, 2420, and 2550 transitions belonging to the ν4, ν7, ν10, and ν12 bands were assigned in the experimental spectrum with the maximum values of quantum numbers Jmax./Kamax., equal to 38/10, 43/21, 33/16 and 52/18, respectively. To make the ro-vibrational analysis physically more suitable, the initial values of the rotational and centrifugal distortion parameters of the studied bands were theoretically estimated by the use of isotopic relations. On that basis, a set of 55 vibrational, rotational, centrifugal distortion, and resonance interaction parameters was obtained from the fit. They reproduce values of 2934 initial “experimental” ro-vibrational energy levels obtained from nonsaturated unblended lines (more than 9500 assigned transitions of the ν4, ν7, ν10, and ν12 bands) with the rms error drms=0.00014cm−1. Ground state parameters of the C213H4 molecule were improved as well.

Rovibrational spectra of DCF3 in the 2000 cm−1 region: A high-resolution study of the v5 = 2 and v2 = v5 = 1 levels

The high-resolution infrared spectrum of DCF3 was investigated in the 2000cm−1 region, with the aim of assigning and analyzing the overtone bands 2ν5 (A1+E), as well as the combination band ν2+ν5 (E). The present paper reports on the first high-resolution study of the v2=v5=1 and v5=2 levels, through the analysis of the combination ν2+ν5 and the overtone 2ν5∓2 bands respectively. This analysis can be thought of as a necessary step toward the reinvestigation of the complicated vibrational pattern in the CD stretching fundamental region.

High resolution FTIR study of the [formula omitted] and [formula omitted] “hot” bands of C2H4

Two weak “hot” absorption bands, ν7+ν10−ν10 and ν10+ν12−ν10, of ethylene, C2H4, were analyzed for the first time with high resolution using the Fourier transform interferometer Bruker IFS-120 HR. As the result of analysis we assigned about 930 and 370 transitions (404 and 185 upper state ro-vibrational energy values) with Jmax.=27, Kamax.=14 and Jmax.=20, Kamax.=9 for the bands ν7+ν10−ν10 and ν10+ν12−ν10, respectively. Strong local resonance interactions of the vibrational state (v10=v12=1) with the five other states, and of the state (v7=v10=1) with the seven other states were taken into account, and a set of 77 varied parameters, which reproduce the initial experimental data with the rms deviation of 6.1×10−4cm−1 which is close to experimental uncertainties, was obtained.

IR absorption spectroscopic study of mixed cobalt substituted lithium ferrites

The IR spectra of Li0.5−(x/2)CoxFe2.5−(x/2)O4 ferrite samples (0≤x≤0.6) prepared by solution combustion method have been reported. The influence of Co substitution is verified. XRD studies confirm the spinel phase formation of ferrites. Lattice constant varies linearly from 8.31Å (x=0) to 8.35Å (x=0.6) with composition. Evidence of two absorption bands in the IR spectra (below 800cm−1) reveals the characteristic feature of spinel ferrite. The IR spectra featured additional three absorption bands around 550, 670 and 705cm−1 for the samples x=0.1 and x=0.6. Absence of bands splitting specifies that Fe ions do not exist in excess form. It is found that high frequency band (ν1), due to tetrahedral (A) group, lies at around 600cm−1 and low frequency band (ν2), due to octahedral (B) group, around 450cm−1. The positions of bands are found to be composition dependent. The IR bands due to tetrahedral complexes shift slightly towards high frequency side with composition upto x=0.4 where as that due to octahedral complexes shift towards lower frequency side with x. Based on the data of absorption bands, force constants (kt, ko) and bond lengths (RA, RB) were estimated. Compositional dependence of force constants is explained on the basis of cation–oxygen bond distances of respective sites and cation distribution.

The ν4, ν9, ν10 and ν6 + ν11 bands of 12CH313CH3 between 1345 and 1557 cm−1

The infrared spectrum of 12CH313CH3 is measured between 1345 and 1560cm−1 using high resolution FT-IR with a 13C-enriched gas sample cooled to 130.3K. The three fundamentals ν4, ν9 and ν10 (at 1374, 1470 and 1468cm−1 respectively) and one combination band ν6+ν11 at 1473cm−1 are analyzed for the first time. The transitions of ν10 (an infrared inactive “g” mode of the ethane) are observed through its resonant coupling with ν9 (corresponding to a “u” mode of normal ethane). Transitions of ν6+ν11 are seen due to its strong coupling to ν9. In general, torsional splitting produces two components (as in normal ethane), but in both ν9 and ν10, there is an additional small splitting of these components with degenerate torsional symmetry wherever the interacting ν10 levels become infrared active (from “g↔u” mixing); this mechanism is investigated. Several ℓ-type resonances with Δℓ=±2 and Δk=∓1 are observed within ν9 and between ν9 and ν10 while the strong interaction between ν9 and ν6+ν11 plays a role in tuning pairs of levels into resonance. As in normal ethane, a detectable K-doubling occurs in the levels k=±2, ℓ=∓1 of ν9, and the parallel band ν4 shows an intensity bias, with the R-transitions markedly stronger than the P-transitions, due to its x,y-Coriolis coupling with ν9. The spectrum is analyzed by adopting an appropriate Hamiltonian model, and vibration–rotation–torsion parameters of the four mentioned vibrational states are determined by the least squares process using 1350 observed transition line positions (RMS deviation 3.24×10−3cm−1). The values of rotational and torsional parameters of the vibrational ground state are also improved or determined anew, from data of the present spectrum. Two supplemental files are provided. One shows the fit of line positions, and the other gives the measured positions and intensities at 130K (with known quantum assignments and lower state energies) so that lines of this molecule can be identified in planetary spectra.

FTIR and Electrical Study of Dysprosium Doped Cobalt Ferrite Nanoparticles

We have studied the role of Dy3+ doping on the XRD, TEM, FTIR, and dielectric and electrical properties of CoFe2O4 at room temperature. Cubic spinel phase of CoFe2−xDyxO4 (x = 0.00, 0.05, 0.10, and 0.15) was synthesized by using different sintering temperatures (300, 500, 700, and 900°C). The two absorption bands ν1 and ν2 are observed in Fourier transform infrared spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites, which show signature of spinel structure of the sample. For the sample sintered at 300°C, the dielectric constant is almost unchanged with the frequency at the particular concentrations of x = 0.00 and 0.05. Similar result is obtained for the sample sintered at 500°C (x = 0.10, 0.15), 700°C (x = 0.05, 0.10, and 0.15), and 900°C (x = 0.05, 0.10). An increase in the dielectric constant was observed for the undoped cobalt ferrite sintered at 500, 700, and 900°C. The values of electrical resistivity of the materials vary from ~105 to 109 Ω-cm.