V3 Band Research Articles

Photoluminiscence and absorption of emission by phonons of indirect transitions in layered GaS single crystals

Absorption in E||b and E⊥c polarizations and photoluminescence at the absorption edge were studied at temperatures range 10–300 K. It was found that the smallest indirect transitions take place from the minimum of conduction band C1 (point M) to the maximum of valence band V1 in the Brillouin zone center (point Γ or nearby). A distance between these extrema is 2.4484 eV at 10 K. In addition, the magnitude of indirect transitions from the second band C2 (point M) to valence band V1 (Brillouin zone center) is 2.4912 eV at 10 K. The splitting of C1–C2 bands in M point of the Brillouin zone is equal to ∼43 meV. The indirect transitions from third conduction band C3 (point K) to valence band V1 in the nearby of Γ point are equal to 2.7683 eV at 10 K. The splitting of conduction bands C2 (point M) and C3 (point K) is higher than one for the splitting C1–C2. It was observed bands associated with self-absorption of photoluminescence emission by phonons with symmetries E1g1+A1g2, A1g2+A1g1 and A1g2+E2g2 involved in indirect transitions.

Full quantum calculations of the line shape for H2O perturbed by Ar at temperatures from 20 to 300 K.

This work theoretically studied the spectral line shape of H2O perturbed by Ar in the temperature range of 20-300K for the pure rotational lines below 360cm-1, as well as three lines (31, 2 ← 44, 1, 54, 2 ← 41, 3, and 73, 5 ← 60, 6) in the v2 band. In order to perform precise dynamical calculations at low collision energies, a full-dimensional long-range potential energy surface was constructed for the H2O-Ar system for the first time to correct the long range of our newly developed intermolecular potential energy surface. Subsequently, the six line-shape parameters (pressure-broadening and -shifting parameters, their speed dependencies, and the complex Dicke parameters) were determined from the generalized spectroscopic cross section by the full quantum time-independent close-coupling approach on this new potential energy surface. Our theoretical results are in good agreement with the available experimental observations. Furthermore, the influence of the speed-dependence and Dicke narrowing effects on the line contour was revealed by comparing the differences among the Hartmann-Tran, quadratic-speed-dependent Voigt, and Voigt profiles. The temperature dependence of each line-shape parameter was further parameterized using the triplet-power-law for three pure rotational 61, 6 ← 52, 3, 41, 4 ← 32, 1, and 31, 3 ← 22, 0 lines. These line-shape parameters will provide a comprehensive set of theoretical references for subsequent experimental measurements.

High-Temperature Line List of Phosphaethyne (HCP).

Phosphaethyne (HCP) has been detected in circumstellar envelopes; its spectroscopic line list is helpful for modeling the relevant atmospheric opacity. We present the first comprehensive line list for HCP(X1Σ+) using robust first-principles methods. The analytical potential energy surface and dipole moment surface were constructed based on 26478 ab initio points from coupled-cluster calculations, along with the considerations of core-valence electron correlation and scalar relativistic effects. The variational nuclear motion program TROVE was used to obtain the ro-vibrational energy levels, Einstein A coefficients, and so on. The J-dependent Coriolis-decoupled Hamiltonian was adopted in the variational calculations with k ≤ 20, and the linear molecule treatment was applied to consider the l-type doubling of the bending vibration. The line list contains almost 0.45 billion transitions between 1.21 million levels with rotational excitation up to J = 200. It covers the wavenumber range of 0-9000 cm-1 (wavelengths above 1.11 μm) and is suitable for temperatures up to 3000 K. The millimeter wave spectra agree well with the experiments, and the Fermi resonance between 2v2 and v3 bands has been reproduced.

Infrared Laser Stark Spectroscopy of Methyl Fluoride in 4He Nanodroplets.

We measured the rotationally resolved infrared spectra of helium solvated methyl fluoride at 3 μm and 10 μm, wherein lies C-H and C-F stretching bands, respectively. The linewidths (FWHM) were found to increase with increasing vibrational energy and range from 0.002 cm-1 in the v3 band (C-F stretch) at ~1047 cm-1, to 0.65 cm-1 in the v4 band (asymmetric C-H stretch) at ~2997 cm-1. In between these two bands we observed the lower and upper components of the Fermi triad bands (ν1/2ν2/2ν5) at ~2859 and ~2961 cm-1. We carried out Stark spectroscopy on the lower band on account of its narrower linewidths (0.04 vs. 0.14 cm-1, respectively). The objective of performing Stark spectroscopy was to see if there is any evidence for a rotational linewidth dependence on the external field strength, due to a reduced difference in between methyl fluorides rotational energy gap and the roton-gap of superfluid helium. We did not find any evidence for such an effect, which we largely attribute to the rotational energy gap not increasing significantly enough by the external field. We point to another molecule (formaldehyde) whose energy levels are predicted to show a more promising response to application of an external field.

Branch dependence of halfwidths: Theoretical analysis of N2-broadened halfwidths of CH3Br in the v6 band

The N2-broadened halfwidths of CH3Br in the ν6 band have been calculated, along with the relaxation matrices W. These calculations employ our modified and refined versions of the Robert-Bonamy formalism. Extensive comparisons between the predicted halfwidths from the models and experimental measurements at T = 296 K are presented. Our latest model very closely matches the measurements. Meanwhile, we considered line mixing effects in the spectral profile of the RQ(j,0) sub-branch. Our method probably yields too large values of the off-diagonal elements of W. Finally, by comparing our calculated halfwidths with the data in HITRAN, we have observed generally good agreement, especially for lines with high values of j. However, the agreement becomes poor for lines with low values of j, deteriorating as j decreases. We identified a factor contributing to this poor agreement: the neglect of branch dependence in the development of HITRAN data. We believe that for lines with low values of j, this oversight undermines the reliability of the halfwidth values of CH3Br in HITRAN.

High-SNR mid-infrared dual-comb spectroscopy using active phase control cooperating with CWs-dependent phase correction.

Mid-infrared (MIR) dual-comb spectroscopy (DCS) is a highly effective method for molecular metrology of rovibrational transition spectra in a quick accurate manner. However, due to limited comb frequency instability, manipulating coherence between two frequency combs to accomplish high-quality spectral analysis in the MIR region is a huge challenge. Here, we developed a comb-teeth resolved MIR DCS based on active phase control cooperating with a CWs-dependent (CWD) interferogram timing correction. Firstly, four meticulously engineered actuators were individually integrated into two near-infrared (NIR) seed combs to facilitate active coherence maintenance. Subsequently, two PPLN waveguides were adopted to achieve parallel difference frequency generations (DFG), directly achieving a coherent MIR dual-comb spectrometer. To improve coherence and signal-to-noise ratio (SNR), a CWD resampled interferogram timing correction was used to optimize the merit of DCS from 7.5 × 105 to 2.5 × 106. Meanwhile, we carried out the measurement of MIR DCS on the methane hot-band absorption spectra (v3 band), which exhibited a good agreement with HITRAN by a standard deviation on recording residual of 0.76%. These experimental results confirm that this MIR DCS with CWD interferogram timing correction has significant potential to characterize the rovibrational transitions of MIR molecules.

Dielectrically modified Nd3+ doped (Ni–Mn) based spinel ferrite Ni0.5Mn0.5NdxFe2-xO4 nanoparticles for energy storage applications

The neodymium doped Ni–Mn based spinel ferrites nanomaterials Ni0.5Mn0.5NdxFe2-xO4 with doping concentration of 0.00–0.20 were synthesized by sol gel auto-combustion method. All the samples in fine powder were annealed at 600 °C in a muffle furnace for 4 h to remove the impurities and absorbed gases. In XRD patterns, the obtained high intense diffraction peak at (311) is good evidence that the prepared materials are spinel ferrites. With the help of Scherer method, the crystallite size was calculated in nanometer ranging from 13 to 19 nm. Further, the calculated crystallite size was correlated with Williams's Hall, modified Scherrer and size strain plot (SSP) method. The study of surface morphology by scanning electron microscopy (SEM) revealed that some grains are non-uniform at different concentration of neodymium. Fourier transform infrared-spectroscopy (FTIR) analysis was used to study the relationship between transmittance and wavenumber. The pattern obtained from tetrahedral and octahedral site represents two frequency band v1 and v2. The electrical properties like dielectric constant, tangent loss, electric modulus and ac conductivity were studied by impedance analyzer in applied frequency range 1 MHz–3 GHz and result was explained by using Maxwell Wigner method. It was found that there are some relaxation peaks were observed at high frequency due to hopping of electrons. By using Vibrating sample magnetometer (VSM), the magnetic properties were studied in the applied magnetic field ranging from -3kOe to 3 kOe. The hysteresis loop shows the decreasing in retentivity (Mr), magnetization (Ms) and coercive field (Hc). In conclusion, these prepared materials are very useful for energy storage device applications.

Potential Induced Protonation of the Second Coordination Sphere in a Hangman-type Iron Porphyrin Complex Promotes HER: Insights via in Situ Raman Spectroelectrochemistry.

The iron-based porphyrin complex containing a bispyridine-based hanging unit termed Py2XPFe was previously used as an effective catalyst for the reduction of protons to molecular hydrogen in solution. Here, the molecular compound was immobilized on a modified gold electrode surface and investigated by spectroelectrochemical methods under catalytic conditions. Immobilization of the Py2XPFe was facilitated using a pyridine-based amine linker molecule grafted to the gold electrode by electrochemical amine oxidation. The linker molecule denoted in this report as Pyr-1 allows for effective coordination of the iron porphyrin compound to the modified gold surface through axial coordination of the pyridine component to the Fe center. Resonance Raman spectroelectrochemistry was performed on the immobilized catalyst in pH 7 buffer at increasing cathodic potentials. This facilitates the electrochemical hydrogen evolution reaction (HER) while concurrently allowing for the observation of the v4, v3, and v2 porphyrin marker bands, which are sensitive to oxidation and spin state changes at the metal center. The observed changes in these bands at decreasing potential indicate that the immobilized Py2XPFe exists in the formal high-spin FeIII state before being reduced to the low-spin FeII state resulting from axial interaction with the linker moiety. This FeII state likely acts as the precatalyst for the HER reaction. Surfaced enhanced Raman spectroelectrochemistry was also conducted on the system as the gold electrode provides a sufficient surface enhancement effect so as to observe the bonding nature of the pyridine substituents within the second coordination sphere. As the potential is lowered cathodically, the pyridine ring breathing modes at 999 cm-1 are shown to increase in intensity due to protonation, which reach an intensity saturated limit whereat HER is conducted. This suggests that in pH 7 buffer, the increase in cathodic potentials facilitates protonation of the pyridine-based second coordination sphere. The extent to which protonation occurs can be viewed as a function of decreasing potential due to an increase in proton flux at the immobilized catalyst which, at the required onset potential for catalysis, aids in the reduction of protons to molecular hydrogen.

High-temperature absorption cross-sections and interference-immune sensing method for formaldehyde near 3.6-µm

Absorption cross-sections of formaldehyde (CH2O) were measured at elevated temperatures near 3.6 µm, a region of strong intensity due to the overlapping QQ5 branch of the v1 band and the PQ7 branch of the v2+v4 combination band. 1,3,5-trioxane was shock-heated in an argon bath gas to produce controlled mixtures of formaldehyde over a range of temperatures (900–1500 K) and pressures (0.4–4.8 atm). Spectrally-resolved absorption measurements of formaldehyde were obtained using a rapidly-tunable distributed-feedback interband cascade laser scanned at 40 kHz over 2778.1–2778.9 cm−1 behind reflected shock waves. The resulting absorption cross-sections were fit with functions reflecting the temperature and pressure dependence of the targeted features, enabling spectral reconstruction at any temperature and pressure within the range of the study. By exploiting the strong temperature and pressure sensitivity of the cross-sections, it is demonstrated that CH2O concentration, temperature, and pressure can be inferred from a measured absorbance spectrum. Cross-sections of common combustion species were also measured over the selected wavelength range to validate that the region is largely free of narrow-band interference. Further, the multi-parameter spectral fitting method is shown to correct for baseline interference and demonstrated in experiments involving transient gas properties.

High-resolution rovibrational spectroscopy of trans-formic acid in the v1 OH stretching fundamental: Dark state coupling and evidence for charge delocalization dynamics

High-resolution infrared (IR) reduced-Doppler absorption spectra of jet-cooled gas phase trans-formic acid in the v1 OH stretching fundamental region are reported for the first time, obtained by supersonically expanding trans-formic acid/Ar mixtures through a slit jet nozzle source and rotationally cooling to Trot ≈ 10.9(5) K, with absorption signals recorded by high-resolution difference-frequency IR absorption spectroscopy. Two a/b-type rovibrational bands of comparable intensity, one ∼10-fold weaker b-type band, and one ∼6-fold weaker a-type band are observed, with vibrational band origins at 3570.493(5), 3566.793(5), 3560.032(9), and 3534.6869(2) cm−1, respectively. Based on previous Raman jet spectroscopic work by Nejad and Sibert [A. Nejad, E.L. Sibert III, The Raman jet spectrum of trans-formic acid and its deuterated isotopologs: Combining theory and experiment to extend the vibrational database, J. Chem. Phys. 154(6) (2021) 064301.], these four rovibrational bands have been assigned to v1, (v2 + v7), (v6 + 2v7 + 2v9), and 2v3, respectively. Specifically, two of the three upper dark states (2171 (a′) and 617292 (a′)) are close enough to the “bright” 11 (a′) state to facilitate strong anharmonic resonance interactions, which results in intensity mixing into the two zero-order bands that would otherwise be “dark”. Furthermore, our high-resolution spectral analysis reveals that there are local rotational crossings between these zero-order 11 and 2171 states resulting in extra lines (i.e., some upper levels in the nominally v1 band have majority zero-order 2171 state character). This motivates development of a 3 coupled state (11, 2171, and 617292) picture to aid in the spectral analysis, which is able to match all 3 observed band origins and relative band intensities, as well as indicate the necessity of multistate (> 2) coupling. Though limited by range of J and Ka levels (J' ≤ 9 and Ka' ≤ 3) populated at supersonic jet temperatures, this work offers first precision spectroscopic analysis of trans-formic acid in the v1 OH stretch region, which should aid in assignment of the more complete yet highly congested room temperature FTIR spectra [D. Hurtmans, F. Herregodts, M. Herman, J. Liévin, A. Campargue, A. Garnache, A. Kachanov, Spectroscopic and ab initio investigation of the νOH overtone excitation in trans-formic acid, J. Chem. Phys. 113(4) (2000) 1535–1545.]. Finally, and in sharp contrast to the spectral complexity in the three predominantly b-type bands, the lone a-type 2v3 rovibrational band at 3534.6869(2) cm−1 is well described by a simple, rigid asymmetric top Hamiltonian.

Raman imaging monitors the time-resolved response of A. thaliana to the artificial inhibition of PSII

The short-term (0–96 h) response of A. thaliana to the oxidative stress induced by PSII inhibitor metribuzin was examined using Raman spectroscopy. Whole leaves of wildtype (WT, Col-0) and ros1 mutant were scanned and changes in carotenoids were examined. Strong differences in Raman intensity distributions between WT and ros1 were observed. A stronger decrease of carotenoid v1(C=C) band intensity across the leaf was observed in ros1 after 48 h of exposure to metribuzin. It can be assumed that higher sensitivity to oxidative stress in ros1 mutant results in significantly faster degradation of carotenoids.

Methyl methacrylate thermal decomposition: Modeling and laser spectroscopy of species time-histories behind reflected shock waves

The thermal decomposition of methyl methacrylate (MMA) was studied through species time-history measurements of formaldehyde (CH2O), carbon monoxide (CO), and carbon dioxide (CO2) behind reflected shock waves over a temperature range of 1200–1600 K near 1 atm. Tunable laser absorption spectroscopy was employed to spectrally and temporally-resolve a cluster of rovibrational lines in the Q-branches of the v1 fundamental band and the v2+v4 combination band of CH2O near 3.60μm, three rovibrational transitions in the P-branch of the fundamental band of CO near 4.98μm, and a transition in the R-branch of the (0100→0101) v3 band of CO2 near 4.19μm. Spectral fitting procedures are subsequently used to infer CO, CO2, and CH2O mole fraction during the pyrolysis of shock-heated mixtures of MMA in argon. These data provided valuable experimental constraints on MMA pyrolysis chemical kinetic models. Sensitivity analysis of a detailed chemical model for MMA decomposition identified specific reactions likely to account for differences observed between the species measurements and simulations of the test conditions. Modified reaction rate parameters for select MMA decomposition reactions are proposed, determined via a genetic algorithm optimization procedure anchored to the speciation data.

High-temperature phase transformations of hydroxylapatite and the formation of silicocarnotite in the hydroxylapatite–quartz–lime system studied in situ and in operando by Raman spectroscopy

Silica-/calcium phosphate ceramics are of high interest in various aspects. On the one hand, they play an important role in medical applications due to their excellent biocompatibility. Therefore, detailed knowledge of the formation and stability properties of the high-temperature products ensures production under controlled conditions. On the other hand, they were identified as sinter deposits in industrial kilns, where it can indicate problems caused by too high combustion temperatures during the thermal combustion processes. Here, we report the results of two Raman heating studies to ~ 1300 °C in 10 °C-steps with nano-crystalline hydroxylapatite (HAp) and tricalcium phosphate (TCP), and a Raman heating study of natural silicocarnotite (to ~ 1200 °C, 50 °C-steps). The Raman experiments were complemented with thermal analyses. The Raman spectra of nano-crystalline HAp recorded at high temperatures revealed the stepwise loss of adsorbed water and surface-bound OH groups until ~ 570 °C. Significant loss of structural OH started at ~ 770 °C and was completed at ~ 850 °C, when HAp transformed to β-TCP. Between ~ 1220 and ~ 1270 °C, β-TCP was found to transform to α-TCP. The room temperature Raman spectrum of silicocarnotite is characterized by an intense v1(PO4) band at 951 ± 1 cm−1 that shifts to ~ 930 cm−1 at ~ 1200 °C. Using hyperspectral Raman imaging with a micrometer-scale spatial resolution, we were able to monitor in operando and in situ the solid-state reactions in the model system Ca10(PO4)6(OH)2-SiO2-CaO, in particular, the formation of silicocarnotite. In these multi-phase experiments, silicocarnotite was identified at ~ 1150 °C. The results demonstrate that silicocarnotite can form by a reaction between β-TCP and α′L-Ca2SiO4, but also between β-TCP and CaSiO3 with additional formation of quartz.

Water ortho-to-para ratio in the coma of comet 67P/Churyumov-Gerasimenko

Context. Abundance ratios of the nuclear-spin isomers of H2O and NH3 have been measured in about two dozen comets, with a mean value corresponding to a nuclear-spin temperature of ~30 K. The real meaning of these unequilibrated nuclear-spin abundance ratios is still debated. However, an equilibrated water ortho-to-para ratio of 3 is also commonly observed. Aims. The H channel of the Visible and Infrared Thermal Imaging Spectrometer (VIRTIS-H) on board Rosetta provided high-resolution 2.5–2.9 μm spectra of H2O vapour in the coma of comet 67P/Churyumov-Gerasimenko (67P), which are suitable for the determination of the ortho-to-para ratio (OPR) of water in this comet. Methods. A large dataset of VIRTIS-H spectra obtained in limb-sounding viewing geometry was analysed, covering heliocentric distances from 1.24 to 2.73 au and altitudes from a few hundred metres to > 100 km. The OPR, together with the H2O rotational temperature and column density, were derived for each spectra using a database of fluorescence synthetic spectra that include both fundamental and hot vibrational water bands. The weak lines of the v1, v1 + v3 − v1 and v2 + v3 − v2 bands in the 2.774–2.910 μm range were used to calculate by how much the strong v3 band centred at 2.67 μm is attenuated due to optical depth effects, expressed by the attenuation factor fatten. Results. Most ortho-to-para ratio determinations are strongly affected by opacity effects, as demonstrated by the observed anti-correlation between the OPR and the column density, and the correlation between the OPR and attenuation factor fatten. Based on both radiative transfer calculations and OPR values obtained in low-opacity conditions, we derive an OPR of 2.94 ± 0.06 for comet 67P. Measured water rotational temperatures show a decrease in gas kinetic temperature with increasing altitude caused by adiabatic cooling. Heliocentric variations are also observed, with warmer temperatures near perihelion. Conclusions. The water ortho-to-para ratio measured in the coma of 67P is consistent with laboratory experiments showing that water vapour that has thermally desorbed from water ice has a statistical value of 3, regardless of the past formation process of water ice.

Experimental investigation on ferrofluid properties of Cd doped Co-Zn ferrites

"Cadmium substituted Co-Zn ferrites 𝐶𝑜0.5𝑍𝑛0.5𝐶𝑑𝑥𝐹𝑒(2−𝑥)𝑂4 (𝑥=0.0, 0.1, 0.2, 0.4, and 0.5) were fabricated by using the Co-precipitation method. The molecular composition and prepared samples of cubic spinel structureswas characterized using X-ray diffraction peak (XRD). X-ray diffraction patterns obtained the most intensive peak at (311) crystallographic planes for x=0.5. Williamson-Hall (W-H) relation was associated with XRD data to determine the crystallite sizes range from 25.356 nm to 35.632 nm and strain value brought into being 0.0024 to 0.0021. Tetrahedral and octahedral sites of hoping length were found to diminish from 3.6707Å-3.6332Å and 2.9967Å-2.9662Å respectively due to the addition of Cd ion concentration. TEM analysis reveals the presence of spherical shape nanoparticles with agglomeration for the prepared samples. It could be referenced based on the investigation of results for molecule size by two XRD and TEM strategies which demonstrate the development of nanomaterials and doping of cobalt ferrites. TEM results are well agreed with the XRD diffraction pattern in crystallite size by using Scherrer’s formula. Fourier Transform Infrared Spectroscopy (FTIR) spectra analysis were carried out on synthesized ferrite samples and observed v1 and v2 strong absorption band in the range 400-4000 cm-1 be the possession to tetrahedral (A) and octahedral (B) sites. In FTIR, the increase of Cd2+ ion in Co-Zn ferrites leads to diminishing peak values towards lower wavenumbers. It is feasible to tune the magnetic characteristics of cobalt ferrite as a potential material for diverse technological applications by substituting Zn2+ and Cd2+ for cobalt magnetic ions."

Structural, dielectric and ac electrical properties of nano-structured Mn0.6Co0.2Ni0.2Fe2O4 ternary ferrite synthesized by citrate-gel auto-combustion technique

The present paper reports the structural, dielectric and ac electrical properties of nanoparticles of mixed polycrystalline spinel ferrite ternary compound Mn0.6Co0.2Ni0.2Fe2O4 synthesized by using the citrate-gel auto-combustion technique. The standard characterization techniques such as EDAX, XRD and FTIR were primarily employed to confirm the elemental stoichiometry, crystallized single-phase, IR-functional groups. These measurements ascertained the formation of monophasic and pure ferrite compound. The powder X-ray diffraction analysis was done to determine the lattice constant(0.8420 nm), crystallite size(21 nm), X-ray density (5.16 g/cm3), distribution of cations among the tetrahedral and octahedral sites of spinel lattice(with iron-Fe3+ distribution ratio among A and B sites is 0.25), bond angles and bond lengths. The theoretical lattice constant is found to be 0.8422 nm. The nature and position of the IR-bands were observed through FTIR spectroscopy. The high-frequency band v1 (A-site vibrations) lies at 563.07 cm-1 while the low-frequency band v2 (B-site vibrations) lies at 462.59 cm-1 . The force constants for the tetrahedral site (kt) and octahedral site (ko) were deduced 1.33×102 N/m and 1.27× 102 N/m, respectively. Frequency dependence of dielectric constant and tangent loss has been explained by the Maxwell Wagner model and Koop's theory. The Jonscher’s power low was used to describe the ac conductivity measurements. The Nyquist and cole-cole plots indicated presence of grain contribution in the conduction mechanism.

High-resolution infrared spectroscopy of supersonically cooled singlet carbenes: Bromomethylene (HCBr) in the CH stretch region.

First high-resolution spectra of cold (∼35K) singlet bromomethylene HCBr in the CH stretching (v1) region from 2770 to 2850cm-1 are reported using near quantum shot-noise limited laser absorption methods in a slit jet supersonic discharge expansion source. Three rovibrational bands are identified at high S/N (20:1-40:1) and rotationally assigned to (i) the CH stretch fundamental (v1) band X̃1,0,0←X̃0,0,0 and (ii) vibrational hot bands [X̃(1,1,0)←X̃(0,1,0) and X̃(1,0,1)←X̃(0,0,1)] arising from vibrationally excited HCBr populated in the discharge with single quanta in either the H-C-Br bend (v2) or C-Br stretch (v3) modes. Precision rotational constants are reported for a total of six states, with an experimentally determined CH stretch vibrational frequency (2799.38cm-1) in good agreement with previous low-resolution fluorescence studies [M. Deselnicu et al., J. Chem. Phys. 124(13), 134302 (2006)]. Detailed analysis of the fundamental v1 band highlights the presence of perturbations in the X̃1,0,0 level, which we tentatively attribute to arise from the nearby triplet state ã(0,0,1) through spin-orbit interaction or the multiple quanta X̃0,2,1 singlet state via c-type Coriolis coupling. Reduced-Doppler resolution (60MHz) in the slit-jet IR spectrometer permits for clear observation of a nuclear spin hyperfine structure, with experimental line shapes well reproduced by nuclear quadrupole/spin-rotation coupling constants from microwave studies [C. Duan et al., J. Mol. Spectrosc. 220(1), 113-121 (2003)]. Finally, the a-type to b-type transition intensity ratio for the fundamental CH stretch band is notably larger than that predicted by using a bond-dipole model, which from high level ab initio quantum calculations [CCSD(T)/PVQZ] can be attributed to vibrationally induced "charge-sloshing" of electron density along the polar C-Br bond.

Characterization of sound enamel and natural white spot lesions

Objective: To compare optical, morphological, chemical, and physical aspects of the sound enamel and whitespot lesions (WSL) classified as ICDAS 2. Material and Methods: Seventeen human molars with one surfacepresenting WSL and a sound surface (2 x 2 mm window) were characterized by Quantitative light-inducedfluorescence (QLF®), Optical coherence tomography (OCT), microhardness, and Raman spectroscopy. The ANOVAand Tukey’s test were used at 5% significance level. Results: The QLF comparison between distinct substratesyielded decreased Q (integrated fluorescence loss) of -15,37%mm2 and -11,68% F (fluorescence loss) forWSL. The OCT detected mean lesion depth of 174,43 um. ANOVA could not detect differences in the opticalattenuation coefficient between the substrates (p>0.05). Lower microhardness measures were observed in WSLthan on sound enamel (p<0.05). The Raman spectra showed four vibrational phosphate bands (v1, v2, v3, v4),where the highest peak was at 960.3 cm-1 (v1) for both substrates. However, a 40% decrease in phosphate (v1)was detected in WSL. The peak at 1071 cm-1 was higher for sound enamel, indicating the presence of a phosphateband instead of the B-type carbonate. The spectra showed higher intensity of the organic composition at 1295 cm-1and 1450 cm-1 for WSL. Conclusion: Non-invasive QLF, OCT and Raman spectroscopy were able to distinguishdifferences in fluorescence, optical properties, and organic/inorganic components, respectively, between soundenamel and WSL, validated by the destructive microhardness analysis. KEYWORDSDental caries; Dental enamel; White-spot lesions; Diagnosis; Raman Spectroscopy.

High Dilutions of a Drug of Covid-19 Origin Show Difference in Ranks

High dilutions (HDs) of drugs, used in Homeopathy, are prepared in aqueous EtOH (ethanol) through serial dilution accompanying mechanical agitation or succussion, and are called potencies. The potencies from the rank 12 onwards are too dilute to contain any original drug molecules. Do the potency ranks show any difference from each other? Do serial dilution and succussion contribute to the difference in potency ranks? This study aims to address these two questions. The throat swab of a Covid-19 patient was preserved and diluted with aqueous EtOH 90% to prepare the mother tincture (MT) and five different potencies of Covid named Covidinum. These potencies and their solvent media were analysed by electronic and vibrational spectroscopy. Charge transfer (CT) and proton transfer interactions occur during preparation of the potencies. The FT-IR spectra of all the test samples after normalization show difference from each other with respect to O-H stretching and bending (v2) bands. Serial dilution and succussion contribute to the observed difference in ranks and CT interactions.

New line positions and effective line intensities of the ν2 band cis-HONO near 1661 cm−1 from quantum cascade laser absorption spectroscopy

High-resolution quantum cascade laser absorption spectrum of cis-HONO of the v2 band has been recorded and analyzed, for the first time, in the mid-infrared region of 1659.2–1662.2 cm−1 (R-branch of the v2 band, N=O stretch). Positions and effective line intensities were determined for about 60 new lines. The absolute absorption frequencies were directly measured during spectral scan using a wavelength meter with an accuracy of ∼0.0017 cm−1. The corresponding simulation spectrum was calculated using the PGOPHER code. The calculated line positions are in a good agreement with the experimentally measured frequencies within the wavelength meter uncertainty. Effective line intensities were determined, with uncertainties of about 17%, by scaling the measured HONO absorption intensities to the previously reported line intensity of a cis-HONO line located in the same spectral region near 1659.85 cm−1.