Ν3 Fundamental Band Research Articles

High resolution FTIR spectroscopy of fluoroform 12CHF3 and critical analysis of the infrared spectrum from 25 to 1500 cm−1

ABSTRACTWe report high-resolution ( 0.001 cm−1) Fourier Transform Infrared spectra of fluoroform (CHF3) including the pure rotational (far infrared or THz) range (28–65 cm−1), the ν3 fundamental ( = 700.099 cm−1), as well as the associated “hot’ band 2ν3 − ν3 ( = 699.295 cm−1) and the ‘atmospheric window’ range 1100–1250 cm−1 containing the strongly coupled polyad of the levels ν2, ν5 and ν3 + ν6, at room temperature and at 120 K using the collisional cooling cell coupled to our Bruker IFS 125 HR prototype (ZP2001) spectrometer and Bruker IFS 125 HR ETH-SLS prototype at the Swiss Light Source providing intense synchrotron radiation. The pure rotational spectra provide new information about the vibrational ground state of CHF3, which is useful for further analysis of excited vibrational states. The ν3 fundamental band is re-investigated together with the corresponding ‘hot’ band 2ν3 − ν3 leading to an extension of the existing line lists up to 4430 transitions with = 66 for ν3 and 1040 transitions with = 43 for 2ν3 − ν3. About 6000 transitions were assigned to rovibrational levels in the polyad ν2/ν5/ν3 + ν6 with = 63 for ν2 ( = 1141.457 cm−1), = 63 for ν5 ( = 1157.335 cm−1) and = 59 for ν3 + ν6 ( = 1208.771 cm−1)( = in each case). The resonance interactions between the ν2, ν5 and ν3 + ν6 states have been taken into account providing an accurate set of effective hamiltonian parameters, which reproduce the experimental results with an accuracy close to the experimental uncertainties (with a root mean square deviation drms = 0.00025 cm−1). The analysis is further extended to the ν4 fundamental ( = 1377.847 cm−1) interacting with 2ν3 ( = 1399.394 cm−1). The results are discussed in relation to the importance of understanding the spectra of CHF3 as a greenhouse gas and as part of our large effort to measure and understand the complete spectrum of CHF3 from the far-infrared to the near-infrared as a prototype for intramolecular quantum dynamics and rovibrational energy redistribution.

High accuracy line positions of the ν1 fundamental band of 14N216O

The ν1 fundamental band of N2O is examined by a novel spectrometer that relies on the frequency locking of an external-cavity quantum cascade laser around 7.8 µm to a near-infrared Tm:based frequency comb at 1.9 µm. Due to the large tunability, nearly 70 lines in the 1240–1310 cm−1 range of the ν1 band of N2O, from P(40) to R(31), are for the first time measured with an absolute frequency calibration and an uncertainty from 62 to 180 kHz, depending on the line. Accurate values of the spectroscopic constants of the upper state are derived from a fit of the line centers (rms ≈ 4.8 × 10−6 cm−1 or 144 kHz). The ν1 transitions presently measured in a Doppler regime validate high accuracy predictions based on sub-Doppler measurements of the ν3 and ν3-ν1 transitions.

Extended analysis of the high resolution FTIR spectrum of 32S16O2 in the region of the ν2 band: Line positions, strengths, and pressure broadening widths

The high resolution infrared spectra of sulfur dioxide (32S16O2) were recorded with a Bruker IFS 125HR Fourier transform infrared spectrometer (Zürich prototype ZP2001) in combination with a Ge:Cu detector and analyzed in the ν2 fundamental band region (400–650 cm−1,ν0˜=517.8725691(77) cm−1). More than 4200 transitions were assigned in the experimental spectra to the ν2 band (the maximum values of the quantum numbers are Jmax.=96 and Kamax.=25). The subsequent weighted fit of experimentally assigned transitions was made with the Watson Hamiltonian. The 148 highly accurate MW transitions known from the literature have been also taken into account in the fit, resulting in a set of 33 parameters which reproduces the initial 1295 infrared ro–vibrational energy values from more than 4200 experimental line positions with a root mean square deviation drms=1.5×10−4 cm−1. An analysis of 992 experimental ro–vibrational line intensities of the ν2 band was made, and a set of four effective dipole moment parameters was obtained which reproduces the initial experimental line intensities with a relative drms=5.7%. The half-widths of 146 ro-vibrational lines (Jmax.=53 and Kamax.=20) were analyzed from the multi-spectrum fit, and self-pressure broadening coefficients were determined.

High-Resolution Infrared Spectra of the ν1 Fundamental Bands of Mono-Substituted 13C Propyne Isotopologues.

We present a combined experimental and ab initio study on the jet-cooled high-resolution infrared spectra of the ν1 (acetylenic stretch) fundamental band for three isotopologues of propyne: 13CH312C≡12CH, 12CH313C≡12CH, and 12CH312C≡13CH. The experimental spectra are recorded in natural abundance using a continuous supersonic expansion of regular propyne diluted in argon and helium, in combination with continuous wave cavity ring-down spectroscopy (cw-CRDS). The fully rotationally resolved K' = 0 and 1 subbands of all three monosubstituted 13C isotopologues have been measured near 3330 cm-1, and their spectroscopic analysis is presented here for the first time. The assignment of the bands and perturbation analysis are assisted by high level ab initio calculations at the CCSD(T) level of theory, from which vibrational frequencies, rotational constants, and Fermi resonances are predicted for each isotopologue.

First pressure shift measurement of ozone molecular lines at 9.54 μm using a tunable quantum cascade laser

Using a free-running distributed-feedback quantum cascade laser (QCL) emitting at 9.54 μm, the pressure shift parameters of four intense rovibrational transitions in the ν3 fundamental band of ozone induced by oxygen (O2), air and the noble gases helium (He), argon (Ar), and xenon (Xe) are obtained by employing second harmonic detection. The experimental analysis comprises a full uncertainty budget and provides line shift data which are traceable to SI. The high density of transitions in the ν3 spectral region of ozone make this region particularly difficult to study with more commonly used techniques such as Fourier transform spectroscopy. The comparatively high spectral resolution of the QCL in the MHz range, on the contrary, allows to measure molecular shifts at relatively low pressures (from 2 to 70 hPa), thus reducing the impact of spectral congestion due to pressure broadening of molecular lines. The comparison of our results with published data shows that presently recommended values for the pressure shift are too low in this region. This observation is corroborated by semi-classical calculations using the Robert-Bonamy formalism. A slight negative J dependence, already observed in other ozone vibrational bands, is predicted. Systematic use of our technique could be very useful to support this hypothesis and to make up for the lack of shift parameters for ozone ν3 transitions in molecular spectral databases. A subsequent stabilization of the QCL onto an optical frequency comb will open up possibilities to perform metrological measurements of Doppler-free molecular lines.

Minimally intrusive optical probe for in situ shock tube measurements of temperature and species via tunable IR laser absorption

An optical probe was developed for in situ laser absorption spectroscopy measurements of target species concentration and temperature near a shock tube endwall. The optical components of a single-ended sensor, including two sapphire rods with a separation of 2.8 cm (effective optical path length), were coupled with a custom-machined shock tube end cap. This hardware design—complemented by a scanned wavelength direct absorption (scanned DA) optical sensing scheme, targeting CO2—enabled minimally invasive, sensitive and spatially resolved measurement of CO2 along the shock tube axis in the reflected shock region. Scanned direct absorption of two adjacent, discrete, rovibrational features in the ν3 fundamental band of CO2 near 4.2 µm, with a single interband cascade laser, allowed measurement of temperature from the ratio of integrated absorbances. Several tests were conducted to validate the accuracy of the sensor and confirm that shock conditions were unperturbed by the probe. The probe-measured temperature and CO2 mol fraction in the reflected shock region, accurate within ~ 1 and ~ 5%, respectively, at a rate of 20 kHz, in shocks with 1–7% carbon dioxide diluted in argon or nitrogen and at temperatures of 1200–2000 K and pressures of 0.7–1.2 bar. Agreement with multiple metrics for validation was confirmed. No evidence of perturbed shock conditions was found.

Infrared spectroscopy of the NO3 radical from 2000 to 3000 cm−1

The present paper reports high-resolution spectroscopic study of the 14NO3 radical in the 2000–3000 cm−1 region, where eight E′-A2′ bands from the ground state are observed. Three bands at 2206, 2246, and 2377 cm−1 are analyzed for the first time, and assigned to the ν1+3ν4, 2ν2+2ν4, and ν3+3ν4 bands, respectively. Bands at 2024, 2155, 2518, and 2585 cm−1 are reassigned to the ν1+ν3, 2ν3, ν1+ν3+ν4, and 2ν3+ν4 bands, respectively, by adopting the new ν3 vibrational frequency of 1055 cm−1 lower than the previous ν3=1492 cm−1. The band at 2902 cm−1 is observed for the first time and assigned to the ν1+ν3+2ν4 band which is the ν1 combined band with the 1927 cm−1 band. Band intensities observed in the 2000–3000 cm−1 region are attributed to the intensity borrowing from the B̃2E′–X̃2A2′ electronic transition through the vibronic interaction. Although the ν3 fundamental band has not been observed due to the cancelation of vibrational intensity and borrowed intensity, the 2ν3 band becomes stronger than ν3 by a factor of more than 50. Perturbation effects are recognized for the bands observed except for the 2206 cm−1 and 2377 cm−1 bands, and are analyzed by taking into account the Coriolis interaction in the most cases. However, the 2024 cm−1 band is free from the Coriolis interaction, and the v1–v3 interaction is incorporated in the analysis, leading to the 2ν1 frequency of 2008.8 cm−1, which is close to the energy value of 2010 cm−1 observed by a laser induced fluorescence study.

High resolution study of the ν2 and ν5 rovibrational fundamental bands of thionyl chloride: Interplay of an evolutionary algorithm and a line-by-line analysis.

The ν2 and ν5 fundamental bands of thionyl chloride (SOCl2) were measured in the 420 cm-1-550 cm-1 region using the FT-far-IR spectrometer exploiting synchrotron radiation on the AILES beamline at SOLEIL. A straightforward line-by-line analysis is complicated by the high congestion of the spectrum due to both the high density of SOCl2 rovibrational bands and the presence of the ν2 fundamental band of sulfur dioxide produced by hydrolysis of SOCl2 with residual water. To overcome this difficulty, our assignment procedure for the main isotopologues 32S16O35Cl2 and 32S16O35Cl37Cl alternates between a direct fit of the spectrum, via a global optimization technique, and a traditional line-by-line analysis. The global optimization, based on an evolutionary algorithm, produces rotational constants and band centers that serve as useful starting values for the subsequent spectroscopic analysis. This work helped to identify the pure rotational submillimeter spectrum of 32S16O35Cl2 in the v2=1 and v5=1 vibrational states of Martin-Drumel et al. [J. Chem. Phys. 144, 084305 (2016)]. As a by-product, the rotational transitions of the v4=1 far-IR inactive state were identified in the submillimeter spectrum. A global fit gathering all the microwave, submillimeter, and far-IR data of thionyl chloride has been performed, showing that no major perturbation of rovibrational energy levels occurs for the main isotopologue of the molecule.

High-resolution Fourier transform emission spectroscopy of the A∼2Πi-X∼2Πi band of the OCS+ ion.

High resolution Fourier transform emission spectroscopy of the A∼2Πi-X∼2Πi band of the OCS+ ion was performed in the UV region to observe the ν1 (CO stretch) progression bands (υ1 = 0 → 2-5) for both the Ω=3/2 and 1/2 spin components. Accurate molecular constants including the rotational constants, B0 = 0.194 765(13) and 0.187 106(13) cm-1, and the spin-orbit interaction constants, A0 = -381.0(56) and -126.5(56) cm-1, were determined for the X∼2Π and A∼2Π states, respectively, by the simultaneous analysis of the observed progression bands. The CO bond length (rCO = 1.2810 Å) for the A∼2Π state, derived from the rotational constant B0 and Franck-Condon factors, is longer by 0.1756 Å than that (1.1054 Å) for the X∼2Π state, while the CS bond length for the A∼2Π state is shorter by 0.0905 Å than that for the X∼2Π state. Pure rotational transition frequencies in the ground X∼2Π state are predicted, as well as transition frequencies of the ν1 fundamental band, with the present molecular constants.

Effective line intensity measurements of trans-nitrous acid (HONO) of the ν1 band near 3600 cm−1 using laser difference-frequency spectrometer

We report on the measurements of the effective line intensities of the ν1 fundamental band of trans-nitrous acid (trans-HONO) in the infrared near 3600cm−1 (2.78µm). A home-made widely tunable laser spectrometer based on difference-frequency generation (DFG) was used for this study. The strengths of 28 well-resolved absorption lines of the ν1 band were determined by scaling their absorption intensities to the well referenced absorption line intensity of the ν3 band of trans-HONO around 1250cm−1 recorded simultaneously with the help of a DFB quantum cascade laser (QCL) spectrometer. The maximum measurement uncertainty of 12% in the line intensities is mainly determined by the uncertainty announced in the referenced line intensities, while the measurement precision in frequency positions of the absorption lines is better than 6×10−4cm−1. The cross-measurement carried out in the present work allows one to perform intensity calibration using well referenced line parameters.

Accurate line intensities for water transitions in the infrared: Comparison of theory and experiment

Ab initio calculations of water intensities are becoming mature and are claimed to have 1% accuracy in many cases. Experimental intensities with 1% accuracy can be achieved with some care. An intercomparison of ab initio against experimental water intensities is presented for a variety of infrared bands for H216O and some for H218O and H217O. A new calculated H216O line list is presented for which uncertainties in the ab initio line intensities are evaluated. Much of the data show agreement within 2% between ab initio and experiment, however, for some bands, notably those involving excitation of some stretching modes, there are larger offsets of up to 8% attributed to ab initio calculation errors but still within the uncertainty of the ab initio calculation. In the ν1 fundamental band differences of between +5% and −13% are found which show systematic dependence on wavenumber, ΔKa, and ΔJ, again attributable to ab initio calculation errors. In the ν2 band, intensity-dependent differences up to 2% originate from the analysis of the experimental data. At present experiments are important to validate ab initio calculations but ab initiopredictions can be very useful in validating the experiment. As the two procedures display significantly different systematic errors, it is suggested that combining both gives the best results; this study will also facilitate further improvements of the theoretical methodology.

High-resolution infrared spectroscopy of CH2D79Br: ro-vibrational analysis of the ν4 and ν8 fundamental bands

ABSTRACTThe high-resolution Fourier transform infrared spectrum of CH2D79Br has been recorded and analysed in the region of the ν4 and ν8 fundamentals located in the range 1125−1360 cm−1. The strong ν4 band, centred at 1225 cm−1, shows an a/b-hybrid structure with predominant a-type character, whereas ν8, at 1253 cm−1, generates a c-type contour comparable in intensity to the b-type component of ν4. The upper states of these fundamentals are coupled through a- and b-type Coriolis resonances; further complications in this band system arise from perturbations due to the ν6 = 2 (1183 cm−1) and ν5 = ν6 = 1 (1359 cm−1) dark states. The former interacts with ν8 = 1 by b-type Coriolis coupling, whereas the latter perturbs the ν4 = 1 and ν8 = 1 levels by anharmonic and a-type Coriolis resonances, respectively. Accurate upper state parameters and interaction terms have been determined for the tetrad system ν4/ν8/2ν6/ν5+ν6 by also including in the dataset the assigned transitions of the 2ν6−ν6 and ν5+ν6−ν6 hot bands obtained from previous analysis.

Combined synchrotron-based high resolution FTIR and IR-diode laser supersonic jet spectroscopy of the chiral molecule CDBrClF

The rovibrational spectrum of Deuterobromochlorofluoromethane CDBrClF has been measured with a resolution of better than 0.001cm−1 at room temperature with the Zurich Bruker IFS spectrometer prototype (ZP 2001) using a globar source, and with the Bruker prototype 2009 interferometer connected to the Swiss Light Source (SLS) synchrotron as a radiation source providing a resolution of 0.0007cm−1 in the range 600–1100cm−1. In addition CDBrClF has been measured at low rotational temperature (Trot=15K) with our diode laser supersonic jet setup around 748cm−1 in the ν5 region (resolution 0.0013cm−1). The spectra of the two major isotopomers CD79Br35ClF and CD81Br35ClF have been analyzed within the ν5 (CCl-stretch, ν̃0=748.2998cm−1 (CD79Br35ClF), ν̃0=748.1541cm−1 (CD81Br35ClF)), ν4 (CF-stretch, ν̃0=1082.8116cm−1 (CD79Br35ClF), ν̃0=1082.7963cm−1 (CD81Br35ClF)) and ν3 (DCF-bend, ν̃0=918.3715cm−1 (CD79Br35ClF), ν̃0=918.0206cm−1 (CD81Br35ClF)) regions. A detailed rovibrational analysis of these bands is presented. A combined analysis of the ν3,ν4 and ν5 fundamental bands provides accurate rotational and quartic centrifugal distortion constants for the vibrational ground state and for the states ν3,ν4 and ν5 of CD79Br35ClF and CD81Br35ClF. The results are discussed in relation to intramolecular (ro)vibrational redistribution (IVR) and also possible experiments pertaining to the experimental detection of molecular parity violation.

Compact optical probe for flame temperature and carbon dioxide using interband cascade laser absorption near 4.2 µm

An in situ thermometry technique was developed for low-pressure flames based on laser absorption spectroscopy of nascent carbon dioxide. Discrete, rovibrational lines within the ν3 fundamental band near 4.2 µm were utilized due to their superior strength, large temperature sensitivity and isolation from interfering absorption lines of other combustion species. These transitions were simultaneously accessed with a single interband cascade laser using scanned-wavelength direct absorption and Voigt lineshape fitting to infer temperature from the ratio of integrated absorbance. A single-ended optical probe constructed of sapphire rods was used to deliver the laser light to the flame. Measurements of temperature and CO2 were conducted in burner-stabilized flames for methane–oxygen and ethylene–oxygen reactant mixtures over a pressure range of 25–60torr and from a distance of 3–23mm above the burner face. Measurements were compared to a 1-D kinetic model as well as thermocouple measurements. The sensor was also used for path-averaged thermometry on a propane torch at 760torr to demonstrate the potential for measurement at atmospheric pressure.

Determination of ν2 fundamental band origin for BeH2 and BeD2 from deperturbation analysis of hot bands.

New vibration-rotation hot bands, i.e., 031 → 030 and 041 → 040, have been assigned and rotationally analyzed for the gaseous BeH2 molecule. The 03(1)0 (Πu), 03(1)1 (Πg), 04(2)0 (Δg), and 04(2)1 (Δu) states are locally perturbed by the nearby 001 (Σu (+)), 002 (Σg (+)), 01(1)1 (Πg), and 01(1)2 (Πu) states, respectively [A. Shayesteh et al., J. Chem. Phys. 118, 3622 (2003)]. Appropriate Hamiltonian matrices have been constructed to take the effects of rotational ℓ-type doubling, ℓ-type resonance, and third order Coriolis interactions into account, and used in deperturbation analyses. From nonlinear least squares fits of all the data, relative energies and unperturbed rotational constants have been determined for the 030, 031, 040, and 041 vibrational levels of BeH2. Similar deperturbation fits were performed for the 001 → 000 and 011 → 010 bands of the BeD2 isotopologue, while the 030 and 040 vibrational levels were treated as dark states. From relative vibrational energies of the 030 and 040 levels, the ν2 fundamental band origins were determined to be 711.48 ± 0.05 cm(-1) and 548.21 ± 0.1 cm(-1) for BeH2 and BeD2, respectively.

The infrared spectrum of the Ar–C2D2 complex

Infrared spectra of Ar–C2D2 are observed in the region of the ν3 fundamental band (asymmetric C–D stretch, ≈2440cm−1) using a tunable optical parametric oscillator to probe a pulsed supersonic slit jet expansion from a cooled nozzle. Transitions are assigned involving K=0–2 in the ground vibrational state, and K=0–4 in the excited state. The intermolecular bending combination band is also observed, giving a bending frequency of 4.798cm−1. Despite this low bending frequency, the Ar–C2D2 spectrum qualitatively resembles that of a normal semi-rigid molecule, in contrast to He– and Ne–C2D2 which are much closer to the limit of free internal rotation.

Optimized approach to retrieve information on atmospheric carbonyl sulfide (OCS) above the Jungfraujoch station and change in its abundance since 1995

In this paper, we present an optimized retrieval strategy for carbonyl sulfide (OCS), using Fourier transform infrared (FTIR) solar observations made at the high-altitude Jungfraujoch station in the Swiss Alps. More than 200 lines of the ν3 fundamental band of OCS have been systematically evaluated and we selected 4 microwindows on the basis of objective criteria minimizing the effect of interferences, mainly by solar features, carbon dioxide and water vapor absorption lines, while maximizing the information content. Implementation of this new retrieval strategy provided an extended time series of the OCS abundance spanning the 1995–2015 time period, for the study of the long-term trend and seasonal variation of OCS in the free troposphere and stratosphere.Three distinct periods characterize the evolution of the tropospheric partial columns: a first decreasing period (1995–2002), an intermediate increasing period (2002–2008), and the more recent period (2008–2015) which shows no significant trend. Our FTIR tropospheric and stratospheric time series are compared with new in situ gas chromatography mass spectrometry (GCMS) measurements performed by Empa (Laboratory for Air Pollution/Environmental Technology) at the Jungfraujoch since 2008, and with space-borne solar occultation observations by the ACE-FTS instrument on-board the SCISAT satellite, respectively, and they show good agreement. The OCS signal recorded above Jungfraujoch appears to be closely related to anthropogenic sulfur emissions.

Intermolecular vibrations of the CO2–CS2 complex: Experiment and theory agree, but understanding remains challenging

The infrared spectrum of the cross-shaped van der Waals complex CO2–CS2 is observed in the region of the CO2 ν3 fundamental band (≈2350cm−1) using a tuneable diode laser to probe a pulsed supersonic slit jet expansion. Two combination bands are assigned, corresponding to the intermolecular torsion and CO2 bend modes, and their positions and rotational structure agree extremely well (<0.1cm−1) with calculations based on a recent ab initio intermolecular potential. The b-type torsional band is well-behaved, but the a-type CO2 bending band is highly unusual, with large shifts between the subband origins for Ka=0, 2, and 4. The shifts may be rationalized as due to tunnelling effects and Ka-dependent perturbations from other intermolecular modes. But even though they are well predicted by our calculations, there is no simple qualitative explanation. The predicted low-lying planar slipped parallel isomer of CO2–CS2 is not observed.

Mid-infrared concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy of a continuous supersonic expansion discharge source

Concentration-modulated noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) is implemented for the first time on a continuous gas-flow pinhole supersonic expansion discharge source for the study of cooled molecular ions. The instrument utilizes a continuous-wave optical parametric oscillator easily tunable from 2.5 to 3.9 μm and demonstrates a noise equivalent absorption of ∼1 × 10(-9) cm(-1). The effectiveness of concentration-modulated NICE-OHMS is tested through the acquisition of transitions in the ν1 fundamental band of HN2 (+) centered near 3234 cm(-1), with a signal-to-noise of ∼40 obtained for the strongest transitions. The technique is used to characterize the cooling abilities of the supersonic expansion discharge source itself, and a Boltzmann analysis determines a rotational temperature of ∼29 K for low rotational states of HN2 (+). Further improvements are discussed that will enable concentration-modulated NICE-OHMS to reach its full potential for the detection of molecular ions formed in supersonic expansion discharges.

Line intensities and temperature-dependent line broadening coefficients of Q-branch transitions in the v2 band of ammonia near 10.4 μm

We report measured line intensities and temperature-dependent broadening coefficients of NH3 with Ar, N2, O2, CO2, H2O, and NH3 for nine sQ(J,K) transitions in the ν2 fundamental band in the frequency range 961.5–967.5cm−1. This spectral region was chosen due to the strong NH3 absorption strength and lack of spectral interference from H2O and CO2 for laser-based sensing applications. Spectroscopic parameters were determined by multi-line fitting using Voigt lineshapes of absorption spectra measured with two quantum cascade lasers in thermodynamically-controlled optical cells. The temperature dependence of broadening was measured over a range of temperatures between 300 and 600K. These measurements aid the development of mid-infrared NH3 sensors for a broad range of gas mixtures and at elevated temperatures.