Ν3 Vibrational Band Research Articles

A New Ab Initio Potential Energy Surface and Rovibrational Spectra for the CO-N2O Complex.

We constructed a new ab initio potential energy surface (PES) for CO-N2O which includes the intramolecular Q3 normal coordinate for the N2O ν3 antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular Q3 coordinate, we obtained the vibrationally averaged PESs for the CO-N2O system in the ground and ν3 excited states of N2O. Each PES features one nearly T-shaped global minimum and one skewed T-shaped local minimum. Based on these obtained PESs of CO-N2O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν3 vibrational band origin shift of the N2O monomer in CO-N2O is 2.7570 cm-1, matching well with the observed value of 2.9048 cm-1. The computed microwave and infrared transition frequencies, as well as the rotational parameters, are consistent with the experimental observations.

MARVEL analysis of high-resolution spectra of thioformaldehyde (H[formula omitted]CS)

We present a comprehensive analysis of the published spectroscopic literature on the main isotopologue of thioformaldehyde (1H212C32S). All reliable experimental transitions from publications over the last 42 years have been extracted and compiled into a consistent dataset with unique quantum number labelling and measurement uncertainties. The dataset covers the ground, ν1, ν2, ν3, ν4, ν5, ν6, and 2ν2 vibrational bands of H2CS. The ν4 and ν6 modes have very close band centres and consequently different data sources had incompatible vibrational assignments. Variational calculations are used as a basis to assign vibrational states of the associated transitions consistently. The transitions could then be processed using the robust MARVEL (Measured Active Rotational-Vibrational Energy Levels) procedure to produce a highly accurate set of 4254 rotation-vibration energy levels up to J=54 and 3729cm−1. The resulting set of labelled empirical-quality energies will be of significant use in the production of a hot molecular line list of H2CS, as well as other spectroscopic and radiative applications given the astrophysical importance of thioformaldehyde.

Development of a Sub-ppb Resolution Methane Sensor Using a GaSb-Based DFB Diode Laser near 3270 nm for Fugitive Emission Measurement.

A challenge for mobile measurement of fugitive methane emissions is the availability of portable sensors that feature high sensitivity and fast response times, simultaneously. A methane gas sensor to measure fugitive emissions was developed using a continuous-wave, thermoelectrically cooled, GaSb-based distributed feedback diode laser emitting at a wavelength of 3.27 μm to probe methane in its strong ν3 vibrational band. Direct absorption spectra (DAS) as well as wavelength-modulated spectra (WMS) of pressure-broadened R(3) manifold lines of methane were recorded through a custom-developed open-path multipass cell with an effective optical path length of 6.8 m. A novel metrological approach was taken to characterize the sensor response in terms of the linearity of different WMS metrics, namely, the peak-to-peak amplitude of the X2f component and the peak and/or the integrated area of the background-subtracted quadrature signal (i.e., Q(2f - 2f0)) and the background-subtracted 1f-normalized quadrature signal (i.e., Q(2f/1f - 2f0/1f0)). Comparison with calibration gas concentrations spanning 1.5 to 40 ppmv indicated that the latter WMS metric showed the most linear response, while fitting DAS provides a traceable reference. In the WMS mode, a sensitivity better than 1 ppbv was achieved at a 1 s integration time. The sensitivity and response time are well-suited to measure enhancements in ambient methane levels caused by fugitive emissions.

Spectroscopic study of the tunneling dynamics in N2-water observed in the O-D stretch region.

The O-D stretch rovibrational spectra of N2-D2O and N2-DOH were measured and analyzed. A combination band involving the in-plane N2 bending vibration was also observed. These bands were recorded using a pulsed-slit supersonic jet expansion and a mid-infrared tunable optical parametric oscillator. The spectra were analyzed by considering the feasible tunneling motions, and transitions were fitted to independent asymmetric rotors for each tunneling state. The rotational constants of the four tunneling components of N2-D2O were retrieved for the excited vibrational states. A two order of magnitude increase in the tunneling splittings is observed for the asymmetric O-D stretch (ν3 in D2O) excitation compared to the symmetric stretch (ν1 in D2O) and to the ground vibrational state. This last finding indicates that the ν3 vibrational state is likely perturbed by a combination state that includes ν1. Finally, the observation of a local perturbation in the ν3 vibrational band, affecting the positions of few rovibrational levels, provides an experimental lower limit of the dissociation energy of the complex, D0 > 120cm-1.

Measurements and calculations of xenon broadening and shift parameters of water vapour transitions for ν1 + ν2 + ν3 band

The water vapour line broadening and shifting of 72 lines in the ν1 + ν2 + ν3 vibrational band of H2O (in the 8603–8997 cm−1 spectral region) induced by xenon pressure were measured with a Bruker IFS HR FTIR spectrometer. These measurements were performed at room temperature, at a spectral resolution of 0.01 cm−1 and over a wide range of Xe pressure. The broadening and shift coefficients were also calculated using a semi-classical method. The intermolecular potential was taken as the sum of the anisotropic atom–atom potential and the effective vibrationally and rotationally dependent isotropic Lennard–Jones potential.The measured coefficients γ and δ were combined with data from the literature on the ν2, ν1, ν3, 2ν1 + 2ν3, 2ν1 + 2ν2 + ν3, and 3ν1 + ν3 bands, and optimal sets of potential parameters were found that gave the best agreement with the measured broadening coefficients. A strong influence of the imaginary part of the scattering matrix on the calculated values of the γ and δ coefficients was observed. The results were compared with those for He-, Ar-, and Kr-broadenings. The measured broadening coefficients were fitted to empirical expressions. The calculated values of the γ and δ coefficients were compared statistically to the measured values.

Experimental and simulated study of line-shape models for measuring spectroscopic parameters using the WM-DAS method — part I: Collisional broadening and absorption coefficients of H2O-Ar system

Wavelength modulation-direct absorption spectroscopy (WM-DAS) was used to investigate absorption line-shape models by measuring the H2O transition at 7299.431 cm−1 in the ν1+ν3 vibrational band perturbed by Ar. The partially Correlated quadratic Speed-dependent Hard-Collision profile (pCqSDHCP) was found to give the best fit with the smallest residuals. The Ar-induced broadening, narrowing coefficients and the absorption coefficients were measured using various profile models with comparisons to pCqSDHCP. The room-temperature pressure dependence of the measured parameters and their differences over the range from 0.3 kPa to 80 kPa (Lorentzian-to-Doppler broadening ratios from 0.06 to 3.5) were studied. The pCqSDHCP was also simulated and fit by the other simplified profiles to further explore the pressure dependence, which compares well with the experimental results. The pressure dependence of the broadening and absorption coefficients for Voigt profile (VP) were analyzed to provide the optimal pressure range when using VP to measure the spectroscopic parameters. The experimental and simulated results allow us to quantify the systematic errors in the pressure broadening and line intensity associated with simplified line shape models.

The H2O Spectrum of the Massive Protostar AFGL 2136 IRS 1 from 2 to 13 μm at High Resolution: Probing the Circumstellar Disk

Abstract We have observed the massive protostar AFGL 2136 IRS 1 in multiple wavelength windows in the near- to mid-infrared at high (∼3 km s−1) spectral resolution using VLT+CRIRES, SOFIA+EXES, and Gemini North+TEXES. There is an abundance of H2O absorption lines from the ν 1 and ν 3 vibrational bands at 2.7 μm, from the ν 2 vibrational band at 6.1 μm, and from pure rotational transitions near 10–13 μm. Analysis of state-specific column densities derived from the resolved absorption features reveals that an isothermal absorbing slab model is incapable of explaining the relative depths of different absorption features. In particular, the strongest absorption features are much weaker than expected, indicating optical depth effects resulting from the absorbing gas being well mixed with the warm dust that serves as the “background” continuum source at all observed wavelengths. The velocity at which the strongest H2O absorption occurs coincides with the velocity centroid along the minor axis of the compact disk in Keplerian rotation recently observed in H2O emission with ALMA. We postulate that the warm regions of this dust disk dominate the continuum emission at near- to mid-infrared wavelengths, and that H2O and several other molecules observed in absorption are probing this disk. Absorption line profiles are not symmetric, possibly indicating that the warm dust in the disk that produces the infrared continuum has a nonuniform distribution similar to the substructure observed in 1.3 mm continuum emission.

Measurements and calculations of krypton broadening and shifting parameters of the ν1 + ν2 + ν3 band of H2O

The water vapor line broadening and shifting for 96 lines in the ν1 + ν2 + ν3 vibrational band (8600–9070 cm−1 spectral range) induced by krypton pressure were measured with Bruker IFS HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm−1 and in a wide pressure range of Kr. The calculations of the broadening coefficients γ and δ were performed in the framework of the semi-classical method. The intermolecular potential was taken as the sum of the anisotropic atom-atom potential and vibrationally and rotationally dependent isotropic Lennard-Jones potential. The measured line-width coefficients γ were fitted to the empirical functions. The coefficients γ and δ calculated in the semi-classical method and using the empirical functions were compared statistically to measurements.

Measurements and calculations of H2-broadening and shift parameters of water vapour transitions of the ν1 + ν2 + ν3 band

ABSTRACTThe water vapour line broadening and shifting for 97 lines in the ν1 + ν2 + ν3 band induced by hydrogen pressure are measured with Bruker IFS 125 HR FTIR spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm−1 and in a wide pressure range of H2. The calculations of the broadening γ and shift δ coefficients were performed in the semi-classical method framework with use of an effective vibrationally depended interaction potential. Two potential parameters were optimised to improve the quality of calculations. Good agreements with measured broadening coefficients were achieved. The comparison of calculated broadening coefficients γ with the previous measurements is discussed. The analytical expressions that reproduce these coefficients for rotational, ν2, ν1, and ν3 vibrational bands are presented.

LED based Fourier transform absorption spectroscopy of D216O in 14,800–15,200 cm−1 spectral region

A study of the vibration-rotation absorption spectrum of the D2O molecule in the range 14,800–15,200 cm−1 has been performed. The spectrum was recorded with the spectral resolution of 0.05 cm−1 using a Fourier Transform Spectrometer coupled to a multi-pass White-type cell providing an optical path length of 34.8 m. A light-emitting diode was used as the radiation source giving a high brightness that resulted in an S/N ratio of measurements of about 104. A total of 162 energy levels belonging to four vibrational states were determined. The rovibrational assignment of 309 transitions attributed to D2O was based on the variational calculations. The observed D216O spectrum is, mainly, formed by transitions belonging to the 4ν1 + 2ν2 + ν3, 6ν1 and the 5ν1 + ν3 vibrational bands centered at 14,979.173, 15,049.52, and 15,050.898 cm−1, respectively. It was found that the calculated line positions might deviate from the observed ones up to 0.8 cm−1 indicating the necessity of further optimization of the potential energy surface for the D216O molecule.

Measurements and calculations of Ar-broadening parameters of water vapour transitions in a wide spectral region

ABSTRACTThe water vapour line-broadening (γ) and shift (δ) coefficients for 310 lines of 10 vibrational bands ν1, ν3, 2ν2, ν1+ ν2, ν2+ ν3, 2ν2 +ν3, 2ν1, ν1+ ν3, 2ν3 and ν1 +2ν2 induced by argon pressure were measured with a Bruker IFS HR 125 spectrometer. The measurements were performed at room temperature, at the spectral resolution of 0.01 cm–1 and over a wide pressure range of Ar. The calculations of the broadening coefficients γ and δ were performed in the framework of the semi-classical method. The intermolecular potential was taken as the sum of the atom–atom potential and the vibrationally and rotationally dependent isotropic induction+dispersion potential. The measured γ and δ were combined with literature data for the ν2 and 3ν1+ν3, 2ν1+2ν2+ν3 vibrational bands, and the optimal sets of potential parameters that gave the best agreement with the measured broadening coefficients for each vibrational band separately were found. Then, combined experimental data of 13 vibrational bands of H2O perturbed by Ar were used to determine the analytical dependence of some potential parameters on vibrational quantum numbers.

Helium broadening parameters of water vapor in the 10,200–11,200 cm−1 spectral region

The He-broadening (γ) and shift (δ) coefficients of 76 rovibrational transitions belonging to the 3ν1, 3ν3, ν1+2ν2+ν3, and 2ν1+ν3 vibrational bands of H2O molecule were measured in the spectral range between 10,200 and 11,200cm−1 with the spectral resolution of 0.01cm−1 using a Bruker IFS 125HR FTIR spectrometer. The calculations of γ and δ were performed in the framework of the semi-classical method. It was shown that the vibrational dependence of the long-range as well as the short-range parts of an isotropic H2O-He interaction potential influencesubstantially the calculated broadening coefficients γ. The vibrationally and rotationally dependent analytical model for the broadening coefficients calculation is presented and discussed.

Alignment of CH3F in para-H2 crystal studied by IR quantum cascade laser polarization spectroscopy.

In order to investigate the alignment of CH3F in para-H2 crystals, high resolution polarization spectroscopy of the ν3 vibrational band is studied using a quantum cascade laser at 1040 cm(-1). It is found that the main and satellite series of peaks in the ν3 vibrational band of CH3F have the same polarization dependence. This result supports the previously proposed cluster model with ortho-H2 in first and second nearest neighbor sites. The observed polarization dependence function is well described by a simple six-axis void model in which CH3F is not aligned along the c-axis of the crystal but tilted to 64.9(3)° from it.

Quantum Cascade Laser Measurements of Line Intensities, N2-, O2- and Ar- Collisional Broadening Coefficients of N2O in the ν3 Band Near 4.5 µm.

This study deals with precise measurements of absolute line intensities, N2-, O2- and Ar- collisional broadening coefficients of N2O in the P-branch of the ν3 vibrational band near 4.5 µm. Collisional broadening coefficients of N2O-air are derived from the N2- and O2- broadening contributions by considering an ideal atmospheric composition. Studies are performed at room temperature for 10 rotational transitions over 2190-2202 cm(-1) spectral range using a distributed-feedback quantum cascade laser. To retrieve spectroscopic parameters for each individual transition, measured absorption line shape is simulated within Voigt and Galatry profiles. The obtained results compare well with previous experimental data available in the literature: the discrepancies being less than 4% for most of the probed transitions. The spectroscopic data reported here are very useful for the design of sensors used to monitor the abundance of N2O in earth's atmosphere.

First observations of H2O and CO2vapor in comet 67P/Churyumov-Gerasimenko made by VIRTIS onboard Rosetta

Context. Outgassing from cometary nuclei involves complex surface and subsurface processes that need to be understood to investigate the composition of cometary ices from coma observations. Aims. We investigate the production of water, carbon dioxide, and carbon monoxide from the nucleus of comet 67P/Churyumov-Gerasimenko (67P). These species have different volatility and are key species of cometary ices. Methods. Using the high spectral-resolution channel of the Visible InfraRed Thermal Imaging Spectrometer (VIRTIS-H), we observed the ν3 vibrational bands of H2O and CO2 at 2.67 and 4.27 μm, respectively, from 24 November 2014 to 24 January 2015, when comet 67P was between 2.91 and 2.47 AU from the Sun. Observations were undertaken in limb-viewing geometry at distances from the surface of 0 to 1.5 km and with various line-of-sight (LOS) orientations in the body-fixed frame. A geometry tool was used to characterize the position of the LOS with respect to geomorphologic regions and the illumination properties of these regions. Results. The water production of 67P did not increase much from 2.9 to 2.5 AU. High water column densities are observed for LOS above the neck regions, suggesting they are the most productive in water vapor. While water production is weak in regions with low solar illumination, CO2 is outgassing from both illuminated and non-illuminated regions, which indicates that CO2 sublimates at a depth that is below the diurnal skin depth. The CO2/H2O column density ratio varies from 2 to 60%. For regions that are in sunlight, mean values between 2 and 7% are measured. The lower bound value is likely representative of the CO2/H2O production rate ratio from the neck regions. For carbon monoxide, we derive column density ratios CO/H2O < 1.9% and CO/CO2< 80%. An illumination-driven model, with a uniformly active surface releasing water at a mean rate of 8 × 1025 s-1, provides an overall agreement to VIRTIS-H data, although some mismatches show local surface inhomogeneities in water production. Rotational temperatures of 90–100 K are derived from H2O and CO2 averaged spectra.

Spectral properties of Ca-sulfates: Gypsum, bassanite, and anhydrite

This study of the spectral properties of Ca-sulfates was initiated to support remote detection of these minerals on Mars. Gypsum, bassanite, and anhydrite are the currently known forms of Ca-sulfates. They are typically found in sedimentary evaporites on Earth, but can also form via reaction of acidic fluids associated with volcanic activity. Reflectance, emission, transmittance, and Raman spectra are discussed here for various sample forms. Gypsum and bassanite spectra exhibit characteristic and distinct triplet bands near 1.4–1.5 μm, a strong band near 1.93–1.94 μm, and multiple features near 2.1–2.3 μm attributed to H2O. Anhydrite, bassanite, and gypsum all have SO4 combination and overtone features from 4.2–5 μm that are present in reflectance spectra. The mid-IR region spectra exhibit strong SO4 ν3 and ν4 vibrational bands near 1150–1200 and 600–680 cm−1 (~8.5 and 16 μm), respectively. Additional weaker features are observed near 1005–1015 cm−1 (~10 μm) for ν1 and near 470–510 cm−1 (~20 μm) for ν2. The mid-IR H2O bending vibration occurs near 1623–1630 cm−1 (~6.2 μm). The visible/near-infrared region spectra are brighter for the finer-grained samples. In reflectance and emission spectra of the mid-IR region the ν4 bands begin to invert for the finer-grained samples, and the ν1 vibration occurs as a band instead of a peak and has the strongest intensity for the finer-grained samples. The ν2 vibration is a sharp band for anhydrite and a broad peak for gypsum. The band center of the ν1 vibration follows a trend of decreasing frequency (increasing wavelength) with increasing hydration of the sample in the transmittance, Raman, and reflectance spectra. Anhydrite forms at elevated temperatures compared to gypsum, and at lower temperature, salt concentration, and pH than bassanite. The relative humidity controls whether bassanite or gypsum is stable. Thus, distinguishing among gypsum, bassanite, and anhydrite via remote sensing can provide constraints on the geochemical environment.

Optical parametric oscillator-based photoacoustic detection of hydrogen cyanide for biomedical applications

A versatile, continuous wave, optical parametric oscillator is used in combination with photoacoustic spectroscopy for long-term trace gas experiments of volatile compounds emitted by biological samples. The optical parametric oscillator-based spectrometer (wavelength near 3 μm, 8-MHz linewidth, output power ∼1 W) is successfully tested for the detection of hydrogen cyanide (HCN) emission from clover leaves, and Pseudomonas bacteria; in addition, the presence of HCN in exhaled human breath is measured. For specific experiments, the spectrometer is operated continuously up to 10 days and has a detection limit of 0.4 parts-per-billion volume of HCN in air over 10 s, using the P8 rotational line in the ν₃ vibrational band of HCN at 3287.25 cm⁻¹. This results in an overall sensitivity of the system of 2.5 × 10⁻⁹ cm-1 Hz⁻¹/².

Fiber-coupled 2.7 µm laser absorption sensor for CO2 in harsh combustion environments

A tunable diode laser absorption sensor near 2.7 µm, based on 1f-normalized wavelength-modulation spectroscopy with second-harmonic detection (WMS-2f), was developed to measure CO2 concentration in harsh combustion flows. Wavelength selection at 3733.48 cm−1 exploited the overlap of two CO2 transitions in the ν1 + ν3 vibrational band at 3733.468 cm−1 and 3733.498 cm−1. Primary factors influencing wavelength selection were isolation and strength of the CO2 absorption lines relative to infrared water absorption at elevated pressures and temperatures. The HITEMP 2010 database was used to model the combined CO2 and H2O absorption spectra, and key line-strength and line-broadening spectroscopic parameters were verified by high-temperature static cell measurements. To validate the accuracy and precision of the WMS-based sensor, measurements of CO2 concentration were carried out in non-reactive shock-tube experiments (P ∼ 3–12 atm, T ∼ 1000–2600 K). The laser was then free-space fiber-coupled with a zirconium fluoride single-mode fiber for remote light delivery to harsh combustion environments, and demonstrated on an ethylene/air pulse detonation combustor at pressures up to 10 atm and temperatures up to 2500 K. To our knowledge, this work represents the first time-resolved in-stream measurements of CO2 concentration in a detonation-based engine.

Water uptake of internally mixed ammonium sulfate and dicarboxylic acid particles probed by infrared spectroscopy

Tropospheric aerosols are usually mixtures of inorganic and organic compounds in variable proportions, and the relative amount of organic fraction can influence the hygroscopic properties of the particles. Infrared spectra of submicrometer internally mixed dry particles of ammonium sulfate (AS) with various dicarboxylic acids (oxalic, malonic, maleic, glutaric and pimelic) have been measured in an aerosol flow tube at several solute mass ratios. The spectra show a notable broadening in the bandwidth of sulfate ion ν3 vibrational band near 1115 cm−1 with respect to pure AS. We attribute these perturbations, that are biggest at AS/organic acid mass ratio near unity, to intermolecular interactions between inorganic ions and organic acid molecules in the internally mixed solids. The water uptake behavior of internally mixed particles has been measured by recording the infrared integrated absorbance of liquid water as a function of relative humidity (RH). The amount of water present in the particles prior to deliquescence correlates partially with the water solubilities of the dicarboxylic acids, and also with the relative magnitudes of intermolecular interactions in the internally mixed dry solids. Phase change of ammonium sulfate in the internally mixed particles with RH has been spectrally monitored, and it is shown that water uptaken before full deliquescence produces structural changes in the particles that are revealed by their vibrational spectra.

Measurements of the Absorption Line Strength of Hydroperoxyl Radical in the ν3 Band using a Continuous Wave Quantum Cascade Laser

Mid-infrared absorption spectroscopy has been applied to the detection of the hydroperoxyl (HO(2)) radical in pulsed laser photolysis combined with a laser absorption kinetics reactor. Transitions of the ν(3) vibrational band assigned to the O-O stretch mode were probed with a thermoelectrically cooled, continuous wave mid-infrared distributed feedback quantum cascade laser (QCL). The HO(2) radicals were generated with the photolysis of Cl(2)/CH(3)OH/O(2) mixtures at 355 nm. The absorption cross section at each pressure was determined by three methods at 1065.203 cm(-1) for the F(1), 13(1,13) ← 14(1,14) transition in the ν(3) band. From these values, the absolute absorption cross section at zero pressure was estimated. The relative line strengths of other absorptions in the feasible emitting frequency range of the QCL from 1061.17 to 1065.28 cm(-1) were also measured, and agreed with values reproduced from the HITRAN database. The ν(3) band absorption strength was estimated from the analytically obtained absolute absorption cross section and the calculated relative intensity by spectrum simulation, to be 21.4 ± 4.2 km mol(-1), which shows an agreement with results of quantum chemical calculations.