Ν3 Band Research Articles

High resolution spectroscopy of asymmetric top molecules in nonsinglet electronic states: the ν3 fundamental of chlorine dioxide (16O35Cl16O) free radical in the X2B1 electronic ground state.

Highly resolved spectra of the 16O35Cl16O isotopologue of chlorine dioxide were recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer in the region of the ν3 band. The analysis was made in the frame of the spin-rotational effective Hamiltonian (in A-reduction and Ir-representation) taking into account spin-rotational coupling operators up to the sixth order and the corresponding reduction of the Hamiltonian. The mathematical description of the ro-vibrational spectra was implemented to the specially created computer program ROVDES. Under the present experimental conditions, we were able to assign more than 5200 spin-rotational transitions to the ν3 band. This number is 2.4 times higher compared to the previous studies available from the literature. The vibrational ground state parameters were improved, and the 2220 upper spin-rotation-vibration energy levels were determined and used as initial data in the inverse spectroscopic problem with the derived effective spin-rotational Hamiltonian. A total of 37 fitted parameters were determined (22 rotational and centrifugal parameters and 15 parameters of spin-rotation coupling). The appearance of strong Coriolis resonance interactions between the (001) and (100) vibrational states in the sets of (001)[N,Ka = 9], (001)[N,Ka = 17], (001)[N,Ka = 18] and (001)[N,Ka = 19] spin-rotation-vibration levels was experimentally observed for the first time and explained. The drms = 1.4 × 10-4 cm-1 reproduction of the initial "experimental" upper ro-vibrational energy values was achieved which is considerably better compared to the use of parameters from a previous study ([J. Ortigoso et al., J. Mol. Spectrosc., 1992, 155, 25-43]).

Direct frequency comb spectroscopy of HCN to evaluate line lists.

We report direct frequency comb spectroscopy of the 2ν1 band of H13CN in the short-wave infrared (λ = 1.56 μm) towards experimental validation of molecular line lists that support observatories like JWST. The laboratory measurements aim to test spectral reference data generated from an experimentally accurate potential energy surface (PES) and an ab initio dipole moment surface (DMS) calculated from quantum chemistry theory. Benchmarking theory with experiment will improve confidence in new astrophysics and astrochemistry inferred from spectroscopic observations of HCN and HNC. Here we describe our instrumentation and initial results using a cross-dispersed spectrometer with a virtually imaged phased array (VIPA).

The bending of C3: Experimentally probing the [formula omitted]-type doubling and resonance

C3, a pure carbon chain molecule that has been identified in different astronomical environments, is considered a good probe of kinetic temperatures through observation of transitions involving its low-lying bending mode (ν2) in its ground electronic state. The present laboratory work aims to investigate this bending mode with multiple quanta of excitation by combining recordings of high resolution optical and infrared spectra of C3 produced in discharge experiments. The optical spectra of rovibronic (Ã1Πu−X̃1Σg+) transitions have been recorded by laser induced fluorescence spectroscopy using a single longitude mode optical parametric oscillator as narrow bandwidth laser source at the University of Science and Technology of China. 36 bands originating from X̃(0v20), v2=0−5, are assigned. The mid-infrared spectrum of the rovibrational ν3 band has been recorded by Fourier-transform infrared spectroscopy using a globar source on the AILES beamline of the SOLEIL synchrotron facility. The spectrum reveals hot bands involving up to 5 quanta of excitation in ν2. From combining analyses of all the presently recorded spectra and literature data, accurate rotational parameters and absolute energy levels of C3, in particular for states involving the bending mode, are determined. A single PGOPHER file containing all available data involving the X̃ and à states (literature and present study) is used to fit all the data. The spectroscopic information derived from this work enables new interstellar searches for C3, not only in the infrared and optical regions investigated here but also notably in the ν2 band region (around 63 cm−1) where vibrational satellites can now be accurately predicted. This makes C3 a universal diagnostic tool to study very different astronomical environments, from dark and dense to translucent clouds.

Near-infrared detection and line intensity measurements of H2S with ECDL source based off-axis integrated cavity output spectroscopy

Hydrogen sulphide (H2S) is an extremely hazardous gas which leads to poisoning at higher concentration. Here, we demonstrate the trace detection and line intensity measurement of H2S by means of efficient and indigenously developed off–axis integrated cavity output spectroscopy (OA-ICOS) technique coupled with an external cavity diode laser operating in near-infrared spectral region. Trace detection of H2S was made with OA-ICOS absorbance spectra of ro-vibrational line (51, 5 → 61, 6 & 50, 5 → 60, 6) centered at ∼ 6344 cm−1 of ν1 + ν2 + ν3 band. A ∼ 600 ppbv limit of detection was achieved for an averaging time of 350 s with Allan deviation analysis. Additionally, line intensities of several degenerate R branch transitions of ν1 + ν2 + ν3 band including 51, 5 → 61, 6 & 50, 5 → 60, 6 transition was experimentally measured with OA-ICOS. The study will be valuable in aiding the spectroscopic databases of H2S and have potential application in extracting molecular concentrations in the planet’s atmospheres.

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.

Simulation of argon induced coupling coefficients of NH[formula omitted] doublets and their speed dependence

We present a theoretical evaluation of collision induced effects on a few typical doublets in the ν4 band of ammonia perturbed by argon. Quantum dynamical calculations performed on two NH3-Ar potential energy surfaces provide pressure broadening and intradoublet generalized cross sections. From these calculations we derive thermally averaged values at various temperatures. The intradoublet coupling terms at room temperature are found to be in good agreement with available data in the literature. In addition, we study the speed dependence of the pressure broadening and intradoublet coupling coefficients. The former show a usual speed dependence, quite important, but the later show a weak speed dependence at least around 296 K and above.

First high resolution infrared spectra of 1-13C-Propane analyses of the ν26 (B2) C-Type, ν8 (A1) and ν9 (A1) B-Type bands

This paper presents the first high resolution (Δν = 0.00096 cm−1) IR investigation of 1-13C - propane. Spectra of the ν9 (A1) CCC skeletal bending mode near 366.40365 cm−1 (B-type band) and the ν26 (B2) methylene (CH2) rocking mode near 748.470 cm−1 (C-type band) were recorded at the Canadian Light Source (CLS) synchrotron. The spectra were assigned both traditionally and with the aid of the PGOPHER program [1]. As only limited MW data are available for this molecule, we had to use the present data to determine a new set of ground state constants that included centrifugal distortion terms. Upper state constants for both bands have been determined that provide a good simulation of the spectra. The analysis also included the strong a-Type Coriolis resonance between the ν26 and 2ν9 states that causes strong perturbation allowed transitions to appear in the spectrum. Hot band lines of the 2ν9-ν9 band were also assigned and included in our analysis of the bending region. In addition, the v8 (A1) CC stretching band at 862.076 cm−1 (B-type band) which somewhat overlapped v26 was included in the analysis as well. The hope is that this data and the derived molecular constants will be useful in identifying isotopic propane lines in Titan and other astrophysical objects.

Led-based Fourier spectroscopy of HD17O in the range of 10000-11300 cm−1. Analysis of the 3ν3 band

We carried out measurements of the rotational-vibrational absorption spectrum of the HD17О molecule in the range of 10,000–11,300 cm−1 using the LED-based Fourier Transform spectroscopy technique. The spectrum was recorded using IFS-125M Fourier Transform spectrometer with a resolution of 0.02 cm−1, at a pressure of 29 mbar, and an optical path length of 2400 cm. The absorption rotational-vibrational spectrum was analyzed using a set of software programs capable of automatic searching and identifying spectral lines and fitting their parameters. As a result of the analysis, the centers and intensities of 698 spectral lines of the HD17О molecule in the 3ν3 band and the rotational energy levels of the vibrational state (003) were determined for the first time. These new experimental energy levels are compared with the results of “global” variational calculations. It was found that despite strong vibrational excitation the simple model of isolated vibrational state and Watson-type effective Hamiltonian describe rotational energy level pattern in the (003) vibrational state very satisfactory, excluding two levels which are strongly perturbed by a local resonance with the (051) state.

Synchrotron-based infrared spectroscopy of the Coriolis perturbed ν6 and ν8 bands of trans-DCOOH

Previously, the Coriolis perturbed ν6 and ν8 bands of trans-DCOOH were analysed using a high-resolution infrared spectrum that only contained lines from the ν6 fundamental; the ν8 fundamental was too weak to be directly observed [Goh et al., Spectrochim. Acta A: Mol. Biomol. Spectrosc.1999, 55, 1309]. Using a long pathlength multireflection cell and highly brilliant synchrotron radiation, we were able to observe the ν8 fundamental with excellent signal-to-noise (in addition to the ν6 fundamental). Analysis of the spectra using PGOPHER and SPFIT resulted in determination of an extensive set of molecular parameters, including two a-axis and four b-axis Coriolis coupling constants. The set features a significant refinement of the ν8 = 1 constants, with a band origin at 873.3848785(83) cm−1, which is ∼ 0.72 cm−1 higher than previously determined.

High sensitivity absorption spectroscopy of acetylene near 770 nm

The Cavity Ring-Down Spectra (CRDS) of acetylene were recorded in the 12933–13087 cm−1 region with sensitivity of 2 × 10−11 cm−1. Six bands of 12C2H2 and one band of 12C13CH2 were assigned in these spectra. The 3ν1+ν3 band is the strongest one lying in this region. The line positions and intensities were recovered from the recorded spectra. The line intensities in this region are reported for the first time. The line positions were modeled using the traditional power series expression in terms of the angular momentum quantum number for an isolated band. The line intensities were modeled using the vibrational transition dipole moment squared and the Herman-Wallis parameters. The recommended line list of acetylene was prepared for the 12887–13084 cm−1 region. It is based on the calculated line parameters. But in the case of the perturbations, the calculated line parameters are substituted by the observed ones. The harmonic basis state compositions of the upper states of the two bands at 12991.08 and 12988.75 cm−1 were considered in detail.

Can two CO2 molecules be simultaneously bound to one Na+ site in NaY zeolite? A detailed FTIR investigation

Efficient CO2 capture is necessary to solve the current environmental problems of global warming. Porous materials are promising for this purpose and adsorption capacity is a critical issue. Large cations in zeolites can often attach two small molecules, but it is not yet well established whether this applies to CO2. Here we present a detailed FTIR spectroscopic study of CO2 adsorption on NaY zeolite. At ambient temperature and pressures up to 50 mbar, Na+⋯O–C–O species are formed and the CO2 molecules are tilted, which allows interaction of the C-atom with framework oxygen. At higher pressure or at lower temperature reorientation of the CO2 molecules occurs, leading to a significant decrease in the extinction of the ν1 and 2ν2 bands and to a gradual red shift of the ν3(13CO2), (ν1+ν3) and (2ν2+ν3) modes with 3 cm−1. At lower temperature, two additional conversions occur: (i) formation of (Na+⋯O–C–O)2 dimers, causing an additional 2-3 cm−1 red shift of the combination bands, and (ii) attachment of a second CO2 molecule to the same Na+ site, resulting in a discrete red shift of ν3(13CO2), (ν1+ν3) and (2ν2+ν3) with 10 cm−1. Addition of N2 or CO to pre-adsorbed CO2 leads to compression of the formal CO2 adsorption layer. The obtained results demonstrate the possibility of simultaneous binding of two CO2 molecules to one cationic site in zeolites which opens up new horizons in the design of high-capacity CO2 adsorbents.

High-resolution infrared and millimeter-wave spectroscopy of CH35Cl3: The v2=v6=1 combination level

The v2=v6 = 1 (∼936.5 cm−1) vibrational level of chloroform CH35Cl3 has been studied for the first time by high-resolution FTIR and millimeter-wave spectroscopy. Like the v6 = 1 and v3=v6 = 1 vibrations, the v2=v6 = 1 level is characterized by an exceedingly small value of |C − B − Cζ| ≈ 2.88 × 10−3 cm−1. Hence, a global l(2,2) resonance connects the (k − 1, l6 = −1) and (k + 1, l6 = +1) sublevels. This quasi-generalized l(2,2) resonance is almost exclusively responsible of the appearance of the ν2 + ν6 combination band, with its Q-branches falling in a narrow region close to the band origin, together with its, partially resolved, clusters of K-lines on the P and R sides of the spectrum, for each value of J.Despite the weakness of the ν2 + ν6 band, more than 3000 infrared transitions have been assigned, with 2 ≤ J ≤ 102 and − 84 ≤ K′′ · ΔK ≤ +89. These Fourier transform infrared data were combined with about 400 mm-wave transition frequencies in the v2=v6 = 1 state, in a simultaneous fit. The results of the least-squares calculations gave, for instance (in cm−1), ν0 = 936.507 616 1 (43), B = 0.109 702 546 5 (21), C = 0.057 000 223 3 (43), Cζ = −0.049 822 158 (74), and q22 = −6.382 793 (93) × 10−5.

Dual-comb quartz-enhanced photoacoustic spectroscopy

Photoacoustic spectroscopy (PAS) using two optical combs is a new-born technique, offering appealing features, including broad optical bandwidths, high resolutions, fast acquisition speeds, and wavelength-independent photoacoustic detection, for chemical sensing. However, its further application to, e.g., trace detection, is jeopardized due to the fundamentally and technically limited sensitivity and specificity. Here, we take a different route to comb-enabled PAS with acoustically enhanced sensitivity and nonlinear spectral hole-burning defined resolution. We demonstrate dual-comb quartz-enhanced PAS with two near-infrared electro-optic combs and a quartz tuning fork. Comb-line-resolved multiplexed spectra are acquired for acetylene with a single-pass detection limit at the parts-per-billion level. The technique is further extended to the mid-infrared (for methane), enabling improved sensitivity. More importantly, we measure nonlinear dual-comb photoacoustic spectra for the 12C2H2 ν1 + ν3 band P(17) transition with sub-Doppler pressure-broadening dominated homogeneous linewidths (e.g., 45.8 MHz), hence opening up new opportunities for Doppler-free photoacoustic gas sensing.

The H2O–CO2 continuum around 3.1, 5.2 and 8.0 [formula omitted]m: New measurements and validation of a previously proposed [formula omitted] factor

The H2O–CO2 continuum has been measured, at room temperature, at discrete spectral points in the 1100–1500, 1800–2000, and 3100–3300 cm−1 intervals. Our results are in good agreement with previous experimental values in the low frequency wing of the ν2 band of H2O when the associated uncertainties are taken into account. Furthermore, they confirm the quality, in this region, of a χ factor previously adjusted on measurements in the 100–1500 cm−1 range, and prove its validity in the blue side of the ν2 band as well as in the region around 3.1 μm, which have been experimentally studied for the first time in this work. Together with recent measurements in the 1.6 μm, 2.3 μm and far infrared regions, our results contribute to the progressive building-up of a data set for the modeling of the absorption by CO2+H2O mixtures throughout the infrared, which is needed for studies of CO2-rich planetary atmospheres.

Analysis of the ν1+ν3 band of T2 16O and the ν 1 + ν 3 and 2ν2 + ν3 bands of DT16O

We present the band of TO and the and bands of DTO that have been analysed for the first time using high-resolution infrared spectra of tritiated water vapour. The spectrum for TO has been recorded from a custom-built light-pipe cell at room temperature using a Bruker 125HR Fourier-transform spectrometer at a resolution of . For the DTO species, an optimised version of the optical cell with 10 times larger maximum activity with regard to previous studies has been employed. For the band of TO, we report 206 new experimental line positions in the range from 4415 to . In the range of 4780–, 356 new experimental line positions of the DTO have been assigned for the band and 161 line positions for the band. The analysis agrees with previous observations showing a systematic shift of the individual line positions compared to the variationally calculated line positions from the Tomsk database. This shift is depending on the rotational quantum number . For each band, the assigned lines were used to determine the spectroscopic constants of the A-reduced Watson-type Hamiltonian.

Concentrated solar-thermal methane pyrolysis in a porous substrate: Yield analysis via infrared laser absorption

In situ compositional analysis via laser absorption spectroscopy is used to characterize the output of a concentrated solar-thermal methane pyrolysis process over a range of test conditions. The novel thermo-chemical process involves directed radiation of a simulated solar source, focused onto a porous carbon felt substrate through which methane flows and decomposes to produce primarily hydrogen gas and graphitic carbon, along with residual hydrocarbons. A mid-infrared laser diagnostic setup has been developed to measure the residual concentrations of light hydrocarbons in the pyrolysis product gas downstream of the reaction zone, with real-time on-line monitoring capability. The infrared absorption sensor utilizes two interband cascade lasers (ICLs) to probe the fundamental C-H stretch vibrational bands, targeting (1) the R(15) manifold of the ν3 band of CH4 as well as one R(14) transition of the ν9 band of C2H4 near 3.16 μm and (2) the RQ3 line cluster of C2H6 near 3.34 μm, respectively. A compositional analysis based on carbon and hydrogen balances is developed to characterize the hydrogen and carbon yields of the pyrolysis process using laser absorption measurements and deposited carbon weight. A range of test conditions are examined with variations of flow rate and solar flux, demonstrating real-time monitoring of product gas composition and sensitivity to operating conditions in variable and transient conditions.

The ν3 band of 16O14N18O: Line positions and intensities

The Fourier transform IR spectra of samples prepared by mixing two gaseous species 18O2/14N16O (1:2) have been recorded in the region of the ν3 band of nitrogen dioxide. The spectra contain the lines corresponding to the ν3 band of the 16O14N18O isotopologue within the 1540–1640 cm−1. In total 1795 lines of the ν3 band of this isotopologue were assigned with the rotational quantum numbers N and Ka up to 51 and 12, respectively, what corresponds to 3487 electron spin-rotation-vibration transitions. The overall measured set of the line positions was used to fit the effective Hamiltonian parameters. The fitted set of the parameters reproduces the observed line positions with an rms of 3.6 × 10−3 cm−1. A selected set of the measured line intensities was used to determine the effective dipole moment parameters describing the line intensities of the ν3 band. The rms deviation of the fit is 5.0%. It was found that the lines with the ΔKa = ±1 are very weak compared to those with the ΔKa =0. At attained sensitivity only few lines with the ΔKa = ±1 were assigned. The measured line intensities lead to the small value of the dipole moment derivatives ratio |(∂μx/∂q3)(∂μz/∂q3)|≈0.139.

Infrared bands of formaldehyde dissolved in liquid krypton at cryogenic temperatures and the vibrational modes ν1, ν2, and ν5 of H2CO in comets and interstellar clouds

The infrared spectra of formaldehyde (H2CO) dissolved in liquid krypton between 125 K and 137 K have been obtained using a Fourier transform infrared spectrophotometer and a low temperature cryostat. Backing pressures higher than 1.5 atm were necessary to liquefy Kr above 120 K. Monomeric formaldehyde in gas phase was prepared by thermal decomposition of para-formaldehyde. Peak positions (ν), wavenumber shifts between the gas and liquid solution spectra (Δν), and full widths at half maximum (fwhm) are reported. The H2CO vibrational frequencies in liquid Kr are slightly lower than the gas phase frequencies at room temperature because of the inertness of the solvent. The Gaussian 16 software package is used to determine the geometry and lowest energy of H2CO at room temperature and at the temperature of the experiment. Fundamental harmonic and anharmonic vibrational frequencies and relative intensities are calculated. The influence of the solvent on fundamental vibrational frequencies is studied using the polarizable continuum model (PCM). When used in conjunction with calculated anharmonic frequencies, the PCM model shows qualitative agreement with experimental frequency shifts and relative intensities in liquid Kr. The presence of H2CO in space is discussed in reference to the ν1 and ν5 absorption bands observed in comets, the ν1 and ν2 absorptions in interstellar clouds, and the lack of detection of the ν4 and ν6 bands of H2CO in the atmosphere of Titan. The carbonyl stretching mode ν2 is suggested as a possible candidate for confirmation and identification of H2CO in space due to its larger strength in comparison to the other modes that have been studied at low temperatures and its characteristic frequency that is completely removed from CO2, CO, H2O and CH3OH vibrational modes.

The nuclear-spin-forbidden rovibrational transitions of water from first principles.

The water molecule occurs in two nuclear-spin isomers that differ by the value of the total nuclear spin of the hydrogen atoms, i.e., I = 0 for para-H2O and I = 1 for ortho-H2O. Spectroscopic transitions between rovibrational states of ortho and para water are extremely weak due to the tiny hyperfine nuclear-spin-rotation interaction of only ∼30 kHz and, so far, have not been observed. We report the first comprehensive theoretical investigation of the hyperfine effects and ortho-para transitions in H2 16O due to nuclear-spin-rotation and spin-spin interactions. We also present the details of our newly developed general variational approach to the simulation of hyperfine effects in polyatomic molecules. Our results for water suggest that the strongest ortho-para transitions with room-temperature intensities on the order of 10-31 cm/molecule are about an order of magnitude larger than previously predicted values and should be detectable in the mid-infrared ν2 and near-infrared 2ν1 + ν2 and ν1 + ν2 + ν3 bands by current spectroscopy experiments.

The Q-branch of ν1+ν3+3ν4 band of 12C2H2 located at 8330 cm−1

The Q-branch of the ν1+ν3+3ν4 cold band of 12C2H2 located at 8330 cm−1 has been observed under one kilometer absorption path length. The analysis leads to a line list for this isolated and strong Q-branch that is missing from spectroscopic databases. This work completes the large update of acetylene data in the ΔP = 13 spectral region (8200 and 8900 cm−1) made in spectroscopic databases (HITRAN and GEISA) in 2020 edition.