Fundamental Band Research Articles

Carbon dioxide mid-infrared sensing based on Dy3+-doped chalcogenide waveguide photoluminescence.

Climate-active gases, notably carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), display fundamental absorption bands in the mid-infrared (mid-IR). The detection and monitoring of those gases could be enabled by the development of mid-IR optical sources. Broadband mid-IR on-chip light emission from rare-earth-doped chalcogenide photonic integrated circuits could provide a compact, efficient, and cost-effective gas sensing solution. Mid-IR photoluminescence of dysprosium-doped selenide ridge waveguides obtained under optical pumping at a telecommunication wavelength (∼1.3 µm) is investigated for Dy3+ ion concentrations in the 2500-10,000 ppmw range. CO2 detection at around 4.3 µm is then demonstrated based on absorption of this broadband mid-IR emission.

Investigation of Magnetic, Electrical and Optical Properties of Soft-Hard Ferrite Composite Synthesized by Sol-Gel Technique

Soft and hard composites of ferrites with compositional formula (NiFe2O4)100-x – (BaFe12O19)x (where x = 0,20,50,60,80,100) were prepared using sol-gel method. The samples were calcined individually at 900 °C and composites in the required proportions were sintered at 1100 °C in a conventional furnace. The coexistence of NiFe2O4 and BaFe12O19 composites has been confirmed by the X-ray diffraction studies and found to be without any impurities. Rietveld analysis of X-ray diffractograms corroborates hexagonal phase with P63/mmc space group for Barium hexaferrite and cubic phase with Fd-3m:2 space group for Nickle ferrite. The surface morphology was investigated by scanning electron microscopy (SEM), and the micrographs are observed to indicate well distributed grains in the exchange coupled composites. Grains of nano-size about 100–300 nm are formed for the composites. The magnetic properties have been studied by VSM and electric properties were studied by measuring the dielectric constant at room temperature. UV; FTIR studies of the samples are exhibiting fundamental absorption bands.

Detailed studies on structural, morphological, optical, magnetic and mossbauer properties of Cu-substituted cobalt ferrite nanoparticles

In this research, the effect on the morphology, structure, optic, magnetic and Mossbauer features of Cu2+ doping in Co1−xCuxFe2O4 (x = 0.0–1.0) nanoparticles fabricated using the sol-gel auto-combustion reaction method were investigated. The mainly pure phase structure of Co-spinel was observed in x-ray diffraction (XRD) patterns. The sizes of crystal were observed in between 28.77–36.25 nm. The fundamental vibrational bands of the nanoparticles have been found at 426 and 602 cm−1 wavelengths via the Fourier transform infrared (FT-IR) spectrum. The most of Co2+ ions are located at the A site and that substitution by Cu+2 ions at the octahedral site for x = 0.0, 0.25, and 0.50. for x = 0.75 content, the Mössbauer results show that some Cu2+ ions are present in both A and B sites. Magnetization measurements at room temperature show that Cu2+ substitution into Co-ferrite significantly changes the magnetic quantities such as coercivity field (Hc), remnant (Mr) and saturation magnetization (Ms). Magnetic hysteresis curves obtained at room temperature show well-known S-shaped features for all nanoparticles with Ms values of 51.5–64.4 emu g−1, Mr values of 31–36 emu g−1 and H c values of 429.5–1447.8 Oe.

Effect of cation distribution on structural and mechanical properties of Y3+ substituted Co-Zn spinel ferrites nanoparticles.

Yttrium (Y3+) substituted Co-Zn spinel ferrite nanoparticles with compositional formula Co0.9Zn0.2YxFe1.9-xO4 (x = 0.0, 0.015, 0.030, 0.045, 0.06) were synthesized by using sol-gel auto-ignition route. The structural and mechanical properties of Co-Zn ferrites were tailored by the replacement of Fe3+ ions by Y3+ ions. Rietveld refined X-ray diffraction patterns of all the samples confirm the cubic spinel structure. Lattice parameter increases with the substitution of Y3+ ions which may be due to the difference in ionic radii. The crystallite size obtained from XRD analysis is found in the nanometer range of 16.8 – 24.7 nm. Distribution of cations over tetrahedral – A and octahedral – B sites have been studied by using X-ray diffraction data and it is found that Y3+ ions prefers the octahedral – B site. Infrared spectra of all the samples were recorded in the wave number range of 300 cm−1 to 800 cm−1 which shows splitting of the two fundamental absorption bands. Two absorption bands (ν1 and ν2) observed in the range 380 – 610 cm−1 are belongs to tetrahedral – A and octahedral – B interstitial sites. The force constants (KO and Kt) and corresponding elastic parameters were determined by using IR data. The stiffness constant (C11), Young’s modulus (E), rigidity modulus (G), bulk modulus (B) and Debye temperature (θD) were found increases with the addition of Y3+ ions.

A theoretical study of propynal under interstellar conditions and beyond, covering low-frequency infrared spectra, spectroscopic constants, and hot bands

ABSTRACTFrom an astrochemical point of view, propynal is a complex organic molecule. Moreover, it is a potential candidate for the formation of prebiotic propanal and propenal. Therefore, this molecule is of particular interest for astrochemical investigations. As it has been detected in the interstellar medium, it is of high relevance in this field of research. Although experimental data are available for the vibrational fundamental bands and rotational constants, experimental data for vibrational overtones and combination bands are scarce and fairly old. Additionally, high-level ab initio calculations are also not reported. In this work, we provide accurate quantum chemical calculations as well as a detailed analysis of vibrational and rovibrational properties for this molecule. The low-frequency spectrum up to $350\, \,\,\text{cm}^{-1}$ has been studied for temperatures between 10 and $300\, \text{K}$. For the same temperature range, partition functions are provided. Furthermore, the impact of hot bands up to room temperature has been investigated. A comparison of our results with experimental data is provided for the rotational constants, geometrical parameters, and a rovibrational spectrum. The underlying potential energy surface within these calculations is based on explicitly correlated coupled-cluster theory and includes up to four-mode coupling terms within an n-mode expansion. The vibrational and rovibrational calculations rely on vibrational and rovibrational configuration interaction theories, respectively.

Investigations on Pressure Broadening Coefficients of NO Lines in the 1←0 Band for N2, CO2, Ar, H2, O2 and He

A tunable diode laser absorption spectroscopy (TDLAS)-based spectrometer employing a mid-infrared (Mid-IR) interband cascade laser (ICL) was developed and used to determine pressure broadening coefficients of two NO absorption transitions at 1914.98 cm−1 and 1915.76 cm−1 in the fundamental (1←0) band (R11.5 Ω1/2 and Ω3/2) for CO2, N2, Ar, O2, He, and H2. For the first time, a reliable and consistent set of six different pressure-broadening coefficients for the NO line has been measured by a consistent approach covering pressures from 100 to 970 mbar at a temperature of 294 K. Air pressure broadening has been calculated based on N2 and O2 coefficients. The stated pressure-broadening coefficients for N2, CO2, Ar, H2, O2, He, and Air have relative errors in the 0.5–1.5% range. For CO2 and H2, broadening results of NO (1←0) band (R11.5 Ω1/2 and Ω3/2) lines are reported for the first time. The results are also compared to previously available literature data. It was found that the broadening coefficients for O2 and Air are in agreement with literature values, whereas results for Ar and He show larger differences.

FTIR synchrotron spectroscopy of lower modes of methyl-D3 mercaptan (CD3SH)

The infrared Fourier transform spectrum of the lower vibrational modes of the CD3SH isotopologue of methyl mercaptan has been recorded using synchrotron radiation at the FIR beamline of the Canadian Light Source. Torsion-rotation structure has been analyzed for a strong parallel band centred at 644 cm−1 and a weaker perpendicular band centred at 727 cm−1, identified respectively with a mixed {in-plane-CD3-rocking/CSH-bending} mode and the out-of-plane CD3 rock. The torsional energies for the latter mode follow well-behaved curves, inverted with respect to the ground state, but those for the former do not display a systematic pattern. Surprisingly, no clear evidence was seen for the C-S stretching fundamental band, in contrast to CH3SH and the analogous CD3OH and CH3OH methanol species for which the corresponding C-S or C-O stretching bands are major features of the spectrum. This mystery prompted an ab initio calculation to compare the CD3SH and CH3SH vibrational frequencies and transition moments. A mode lying in the expected position was indeed predicted for CD3SH but with almost vanishing intensity. The calculated reduced mass and effective force constant for this mode corresponded closely to those for the C-S stretch of normal CH3SH, indicating that an anticipated strong C-S stretching band is in fact almost completely extinguished for CD3SH.

Potential energy surfaces and bound state calculations for Ne–CO complex: rovibrational spectra and isotope effects

The intermolecular potential energy surfaces (PESs) of Ne–CO complex have been constructed by using the CCSD(T)-F12a method with the aug-cc-pVQZ basis set. These PESs were subsequently applied to investigate the microwave and infrared spectra via bound state calculations. Firstly, compared to the available microwave data, the pure rotational transitions with K = 0 and J ≤ 4 for this complex can be well reproduced. Furthermore, a set of accurate spectroscopic parameters were deduced for the fundamental (v CO = 1) and overtone (v CO = 2) bands. The vibrational shift for the normal isotopologue (Ne–12C16O) was determined to be –0.0683 cm−1, which is in excellent agreement with the experimental observation of –0.0711 cm−1. Isotope effects were also investigated, and the determined rotational constants and vibrational shifts display a fairly good linear relationship, which is classified into two types according to the 12C and 13C in the CO monomer.

Mid-infrared telemetry sensor based calibration gas cell for CO detection using a laser wavelength locking technique

A CO telemetry sensor was designed based on the quantum cascade laser-tunable diode laser absorption spectroscopy (QCL-TDLAS) technology using the fundamental frequency absorption band of CO gas molecules at 4.58 μm. A Fresnel lens with a diameter of 250 mm is utilized to achieve a large area of light collection. The application of light beam tracking method realizes the visualization of telemetry optical path and improves the target tracking capability of telemetry system. Laser wavelength locking technique are investigated to lock the sensor wavelength, thus solving the wavelength drift caused by environmental temperature changes. The second harmonic/laser power signal technique based on wavelength modulated spectroscopy(2f/LPS-WMS) is used to reduce the interference of background noise and laser power intensity by normalizing the second harmonic (2f) with the laser power signal (LPS). Several gas telemetry experiments were performed to verify the sensor performance and the positive linear response of the sensor for CO telemetry was demonstrated. The sensor was tested for stability for approximately 1 h and the Allan -Werle deviation was analyzed. The minimum limit of detection (LOD) of the sensor was 23.07 ppb·m with an averaging time of 62 s. The sensor was reportedly deployed outdoors for the measurement of CO concentration in atmospheric environments.

Optical properties of Ga-Ge-Sb-Se chalcogenide glasses doped with terbium and dysprosium ions, near the fundamental absorption band edge

In the paper, results of measurements of the optical response of chalcogenide glasses of the Ga5Ge20Sb10Se65 composition doped with rare-earth ions Tb3+ or Dy3+, in the wavelength range of 0.7-1.5 μm by the method of IR spectroscopy are presented. Parameters characterizing the fundamental absorption band edge of the glasses --- optical bandgap energy, Urbach tail parameter and weak absorption tail parameter --- have been evaluated. It has been found that doping in low concentrations (up to 0.3 wt%) does not influence the optical bandgap energy and optical properties of the glasses in the range of the Urbach tail, but in the range of the weak absorption tail, optical response of the glasses depends on the activator concentration. Crystallization of the glasses produced by the direct melting method also depends on the activator concentration. In the glasses doped with Dy3+, absorption bands of the ion are located in the range of the weak absorption tail of the glass that makes possible energy transfer between the ions and the gap states of the charge carriers. Keywords: rear earth elements, chalcogenide glasses, bandgap energy, Urbach tail, weak absorption tail, gap states.

The Daniel K. Inouye Solar Telescope (DKIST) Cryogenic Near-Infrared Spectro-Polarimeter

The Cryogenic Near-Infrared Spectro-Polarimeter (Cryo-NIRSP) is a combination slit-based spectrograph and context-imaging instrument designed and built for the National Science Foundation’s Daniel K. Inouye Solar Telescope (DKIST). It is optimized for polarimetric observations of spectral band-passes between 1 and 5 microns, which makes it uniquely suited for polarimetric observations of the solar corona, while also enabling access to other important infrared diagnostics such as the CO fundamental band at 4.6 microns. Integration, testing, and commissioning occurred between 2019 and 2020, and it is now conducting science experiments as part of DKIST early operations. In this article, we discuss its science mission, the requirements driving the design, its fabrication and installation, current capabilities, and the first science data.

Оптические свойства халькогенидных стекол системы Ga-Ge-Sb-Se, легированных ионами тербия и диспрозия, вблизи края полосы фундаментального поглощения

In the paper, results of measurements of the optical response of chalcogenide glasses of the Ga5Ge20Sb10Se65 composition doped with rare-earth ions Tb3+ or Dy3+, in the wavelength range of 0.7 – 1.5 μm by the method of IR spectroscopy are presented. Parameters characterizing the fundamental absorption band edge of the glasses - optical bandgap energy, Urbach tail parameter and weak absorption tail parameter - have been evaluated. It has been found that doping in low concentrations (up to 0.3 mass%) does not influence the optical bandgap energy and optical properties of the glasses in the range of the Urbach tail, but in the range of the weak absorption tail, optical response of the glasses depends on the activator concentration. Crystallization of the glasses produced by the direct melting method also depends on the activator concentration. In the glasses doped with Dy3+, absorption bands of the ion are located in the range of the weak absorption tail of the glass that makes possible energy transfer between the ions and the gap states of the charge carriers.

Comb-based FTIR spectroscopy of CO perturbed by N2 at 4.6 µm

Line-shape measurements of the fundamental vibrational band of CO at 4.6 µm perturbed by N2 with a mid-infrared frequency comb-based Fourier-transform spectrometer were performed. Precise collisional line-shape parameters for 41 lines were determined, including the pressure broadening and shifting and speed-dependence of the collisional width. The results were compared with sparse literature data available.

High-resolution ro-vibrational and rotational spectroscopy of HC3O.

The ro-vibrational and pure rotational spectra of the linear ion HC3O+ have been investigated in a 4 K cryogenic ion trap instrument. For this, a novel action spectroscopic technique, called leak-out-spectroscopy (LOS, Schmid et al., J. Phys. Chem. A 2022, 126, 8111), has been utilized and characterized. In total, 45 ro-vibrational transitions within the fundamental band of the ν1 C-H stretching mode were measured with a band center at 3237.132 cm-1, as well as 34 lines from the combination band ν2 + ν4, and 41 lines tentatively identified as the combination band ν2 + ν5 + ν7, interleaved and resonant with ν1. Surprisingly, also two hot bands were detected despite the cryogenic operation temperature. Based on the novel action spectroscopy approach, a new double-resonance rotational measurement scheme was established, consisting of rotational excitation followed by vibrational excitation. Seven rotational transitions were observed between 89 and 180 GHz. Highly accurate spectroscopic parameters were extracted from a fit using all available data. In addition, a pulsed laser system has been employed to record a low resolution vibrational spectrum, in order to demonstrate the compatibility of such lasers with the LOS method.

Accurate absolute frequency measurement of the S(2) transition in the fundamental band of H2 near 2.03 μm.

A series of spectra of the quadrupolar electric S(2) transition of H2 in the 1-0 band near 4917 cm-1 has been recorded at seven pressure values between 2 and 100 Torr. The comb-referenced cavity ring down spectroscopy (CR-CRDS) technique was used for the recording of this very weak transition. The accuracy of the spectrum frequency axis is achieved by linking the CRDS setup to an optical frequency comb referenced to a GPS-referenced 10 MHz rubidium clock. Applying a multi-spectrum fit procedure to the seven averaged spectra with a quadratic speed dependence Nelkin-Ghatak profile, the transition frequency is determined (ν0 = 147 408 142 357 kHz) with an uncertainty of 150 kHz (∼1 × 10-9 in relative). This represents the smallest uncertainty achieved so far for a transition in the fundamental band of H2. The experimental frequency reported in this work is 1.53 MHz higher than the best-to-date theoretical value. This difference represents 1.5 times the 1σ-uncertainty (about 1 MHz) of the calculated frequency. The measurements also allow for the determination of the absolute intensity value of the S(2) line which shows an agreement with the ab initio value at the per mil level. In addition, the cross section of the collision induced absorption (CIA) underlying the S(2) line is accurately retrieved from the quadratic pressure dependence of the baseline level of the recorded spectra.

High-resolution rovibrational and rotational spectroscopy of the singly deuterated cyclopropenyl cation, c-C3H2D.

Applying a novel action spectroscopic technique in a 4 K cryogenic ion-trap instrument, the molecule c-C3H2D+ has been investigated by high-resolution rovibrational and pure rotational spectroscopy for the first time. In total, 126 rovibrational transitions within the fundamental band of the ν1 symmetric C-H stretch were measured with a band origin centred at 3168.565 cm-1, which were used to predict pure rotational transition frequencies in the ground vibrational state. Based on these predictions, 16 rotational transitions were observed between 90 and 230 GHz by using a double-resonance scheme. These new measurements will enable the first radio-astronomical search for c-C3H2D+.

Spin-orbit splitting and piezoelectric properties of Janus Ge2XY (X ≠ Y = P, As, Sb and Bi).

The coexistence of spin-orbit coupling and piezoelectricity in a single material may have potential application in multifunctional devices, including spintronics, nanorobotics and piezotronics. Spin-orbit coupling provides a new means to manipulate electron's spin without an additional external magnetic field, while piezoelectricity refers to the interplay between mechanical stresses and electric polarization. Using first-principles calculations, the structural, electronic, optical, spin, and piezoelectric properties of the Janus Ge2XY (X ≠ Y = P, As, Sb, and Bi) monolayers were systematically investigated. All the Ge2XY are energetically and dynamically stable in the α phase. At the GW level, Ge2AsSb, Ge2AsBi, and Ge2SbBi have direct fundamental band gaps of 0.65, 0.64, and 0.91 eV. At the GW + BSE level, their optical gaps are 0.42, 0.45, and 0.63 eV, and the optical absorption coefficients can reach about 10-5 cm-1 in the infrared light region, which reveals that they have potential for application in infrared photodetectors. For Ge2PBi, Ge2AsBi, and Ge2SbBi containing the heavy Bi element, the lowermost conduction band and uppermost valence band have large spin splitting along the M-K and K-Γ lines, and the bands near the Fermi level possess Rashba spin splitting at the Γ point. Ge2PBi and Ge2SbBi have both large in-plane piezoelectric coefficients d11 (-0.75 and -3.18 pm V-1) and out-of-plane piezoelectric coefficients d31 (0.37 and 0.30 pm V-1). Our findings are helpful to understand the mechanism of the spin-orbit physics and piezoelectricity of Janus Ge2XY monolayers and guide experiments in exploring novel multifunctional materials.

Real-time, in situ measurement of H2O generated during in situ combustion tests using 1f-normalized wavelength modulation spectroscopy with second harmonic detection.

The development and deployment of a real-time, in situ, non-invasive sensor to monitor the concentration of H 2 O during in situ combustion (ISC) experiments with a heavy-crude oil is described. A real-time sensor to monitor the gas-phase products from ISC can support the study of the kinetics of the complex chemical reactive system in ISC. The mole fraction of H 2 O was measured using tunable diode laser (TDL) absorption spectroscopy coupled with 1f-normalized wavelength modulation spectroscopy (WMS) and 2f detection. The WMS 2f/1f strategy was used to enhance sensitivity with effective noise rejection, particularly suitable when characterizing the water vapor evolved from oil-water emulsions. H 2 O was measured at 3934.10c m -1 from the fundamental band v 3. That transition was selected using the HITRAN database to increase the line strength and minimize interference from neighbor compounds. Measurements of H 2 O concentration were conducted at ambient temperature and pressure using a reference cell (H 2 O=2% at 98.6kPa) to validate the sensor architecture under controlled laboratory environments. The TDL sensor was also successfully validated during real ISC experiments involving heavy-crude oil. Validation and combustion experiments showed the potential of the TDL-based sensor for non-invasive, real-time, in situ measurements of gas-phase species in conditions similar to those of laboratory-scale experimental ISC tests.

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.

Fully quantum calculations of the line shape parameters for 1-0 P(22) and P(31) lines of CO perturbed by He or Ar.

This work reports the full quantum calculations of the spectral line shape parameters for the P(22) line of 13CO and the P(31) line of 12CO in the fundamental band perturbed by He or Ar from 20 to 1000K for the first time. The generalized spectroscopic cross sections of CO-He/Ar indicate that the Dicke narrowing effect competes with the pressure broadening effect. The pressure broadening can be explained by the dynamic behaviors of intermolecular collisions. The intermolecular inelastic collisions contribute more than 95% to the pressure broadening in both CO-He and CO-Ar systems at high temperatures. Regarding the state-to-state inelastic contributions to pressure broadening, the maximum contribution out of the final state of a given line is close to that out of the initial state. The Dicke narrowing effect influences the line shape profile significantly at high temperatures, which suggests that it is indispensable for reproducing the spectral line profile. With the Dicke narrowing effect, the calculated pressure-broadening coefficients and spectral intensity distribution are in good agreement with the available experimental observations.