High-resolution Fourier Transform Infrared Research Articles

Fiducial Reference Measurement for Greenhouse Gases (FRM4GHG)

The Total Carbon Column Observing Network (TCCON) and the Infrared Working Group of the Network for the Detection of Atmospheric Composition Change (NDACC-IRWG) are two ground-based networks that provide the retrieved concentrations of up to 30 atmospheric trace gases, using solar absorption spectrometry. Both networks provide reference measurements for the validation of satellites and models. TCCON concentrates on long-lived greenhouse gases (GHGs) for carbon cycle studies and validation. The number of sites is limited, and the geographical coverage is uneven, covering mainly Europe and the USA. A better distribution of stations is desired to improve the representativeness of the data for various atmospheric conditions and surface conditions and to cover a large latitudinal distribution. The two successive Fiducial Reference Measurements for Greenhouse Gases European Space Agency projects (FRM4GHG and FRM4GHG2) aim at the assessment of several low-cost portable instruments for precise measurements of GHGs to complement the existing ground-based sites. Several types of low spectral resolution Fourier transform infrared (FTIR) spectrometers manufactured by Bruker, namely an EM27/SUN, a Vertex70, a fiber-coupled IRCube, and a Laser Heterodyne spectro-Radiometer (LHR) developed by UK Rutherford Appleton Laboratory are the participating instruments to achieve the Fiducial Reference Measurements (FRMs) status. Intensive side-by-side measurements were performed using all four instruments next to the Bruker IFS 125HR high spectral resolution FTIR, performing measurements in the NIR (TCCON configuration) and MIR (NDACC configuration) spectral range. The remote sensing measurements were complemented by AirCore launches, which provided in situ vertical profiles of target gases traceable to the World Meteorological Organization (WMO) reference scale. The results of the intercomparisons are shown and discussed. Except for the EM27/SUN, all other instruments, including the reference TCCON spectrometer, needed modifications during the campaign period. The EM27/SUN and the Vertex70 provided stable and precise measurements of the target gases during the campaign with quantified small biases. As part of the FRM4GHG project, one EM27/SUN is now used as a travel standard for the verification of column-integrated GHG measurements. The extension of the Vertex70 to the MIR provides the opportunity to retrieve additional concentrations of N2O, CH4, HCHO, and OCS. These MIR data products are comparable to the retrieval results from the high-resolution IFS 125HR spectrometer as operated by the NDACC. Our studies show the potential for such types of spectrometers to be used as a travel standard for the MIR species. An enclosure system with a compact solar tracker and meteorological station has been developed to house the low spectral resolution portable FTIR systems for performing solar absorption measurements. This helps the spectrometers to be mobile and enables autonomous operation, which will help to complement the TCCON and NDACC networks by extending the observational capabilities at new sites for the observation of GHGs and additional air quality gases. The development of the retrieval software allows comparable processing of the Vertex70 type of spectra as the EM27/SUN ones, therefore bringing them under the umbrella of the COllaborative Carbon Column Observing Network (COCCON). A self-assessment following the CEOS-FRM Maturity Matrix shows that the COCCON is able to provide GHG data products of FRM quality and can be used for either short-term campaigns or long-term measurements to complement the high-resolution FTIR networks.

High-resolution FTIR spectroscopy and analysis of the K a = 0 ← 1 subbands of the fundamentals ν 3 and ν 6 of the dimer (HF)2

We report new far-infrared spectra of (HF)2 obtained by high resolution long-path Fourier Transform-Infrared (FTIR) spectroscopy. The origins of the two tunneling components of the K a = 0 ← 1 subband of the in-plane symmetric bending fundamental ν 3 were found to be at 450.4546 cm − 1 (Γ t : A + ← B +) and at 451.4583 cm − 1 (B + ← A +), and of the K a = 0 ← 1 subband of the out-of-plane bending fundamental ν 6 at 382.0802 cm − 1 (A + ← A +) and at 383.2245 cm − 1 (B + ← B +). The K a = 0 term values with respect to the ground state Γ t = A + term are 486.9442 cm − 1 for the A + and 486.8834 cm − 1 for the B + tunneling levels of ν 3. They are 417.5053 cm − 1 for the A − and 419.7140 cm − 1 for the B − vibration-tunneling sublevels of ν 6. The results are discussed in relation to full-dimensional quantum dynamics and predictions based on recent ab initio calculations and our empirically refined potential energy hypersurfaces. Graphical abstract

Vibrational bands of formaldoxime isotopologue 13CD2NOH in the 280–4000 cm−1 region and rovibrational analysis of its [formula omitted] band by Fourier transform infrared (FTIR) spectroscopy

A total of 11 fundamental and 3 overtone bands of the formaldoxime isotopologue 13CD2NOH were identified using its Fourier transform infrared (FTIR) spectra which were recorded with a low resolution (0.50 cm−1) in the 500–4000 cm−1 region, and high resolution (0.00096 cm−1) in the 280–500 cm−1 region. Their relative infrared (IR) band intensities were also measured. Furthermore, a rovibrational analysis of the IR transitions of the ν12 band of 13CD2NOH was carried out using its high-resolution FTIR spectrum which was recorded at the Australian Synchrotron. A total of 1077 IR transitions of the C-type ν12 band were assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive its band center and the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms for the first time, with a root-mean-square (rms) deviation of 0.00044 cm−1. The band center of the ν12 band of 13CD2NOH were found to be 391.054446(36) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by fitting 407 ground state combination differences (GSCDs) derived from the assigned IR transitions of the ν12 band of 13CD2NOH of this work. The rms deviation of the GSCD fit was 0.00040 cm−1. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 state of 13CD2NOH were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rovibrational constants of 13CD2NOH for both ground and v12 = 1 states. The vibrational anharmonic frequencies of the 12 fundamental bands of 13CD2NOH in the 280–4000 cm−1 region, and their IR band intensities were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data. Finally, the ground state rotational constants and the band center of the ν12 band of the cis conformer of 13CD2NOH were calculated and compared with those of the trans conformer of this work.

Fourier transform infrared (FTIR) spectroscopy of formaldoxime isotopologue 12CD2NOH in the 300–3700 cm−1 region and its ν12 and ν9 bands: Vibrational and rovibrational analyses

The Fourier transform infrared (FTIR) spectrum of the formaldoxime isotopologue 12CD2NOH was recorded in the 500–3700 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental, overtone and combination bands and to measure their relative infrared (IR) band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of ν12 and ν9 bands of 12CD2NOH was recorded in Australian Synchrotron in the 300–510 cm−1 region for a rovibrational analysis. A total of 1060 IR transitions of the C-type ν12 band were fitted using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.000524 cm−1. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to all 5 quartic centrifugal distortion terms were derived for the first time. The band center of the ν12 band of 12CD2NOH was found to be 391.214740(46) cm−1. The ground state rovibrational constants up to all 5 quartic terms were determined for the first time by the fitting of 423 ground state combination differences (GSCDs) derived from the IR transitions of the ν12 band of 12CD2NOH of this work. The rms deviation of the GSCD fit was 0.000473 cm−1 using the Watson’s A-reduced Hamiltonian in the Ir representation. Furthermore, a total of 724 IR transitions of the predominantly B-type ν9 band of 12CD2NOH were fitted with a rms deviation of 0.000360 cm−1 to derive the band center at 465.151277(39) cm−1 and rovibrational constants of the v9 = 1 state up to 4 quartic terms for the first time. Additionally, all 3 rotational constants and 5 quartic centrifugal distortion terms of the ground state and 3 rotational constants of the v12 = 1 and v9 = 1 states of 12CD2NOH were computed from theoretical anharmonic calculations at 2 different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. Close agreement was found for the calculated and experimental rotational constants of 12CD2NOH for the ground, v12 = 1 and v9 = 1 states. The vibrational frequencies (cm−1) of 12 fundamental bands of 12CD2NOH in the 300–3700 cm−1 region, and their IR band intensities (km/mol) were also calculated using B3LYP and MP2 with the cc-pVTZ basis set, and they were compared with the respective experimental data.

Ground-based remote sensing of nitrous oxide (N2O) over Hefei, eastern China from high-resolution solar spectra

ABSTRACT We for the first time demonstrate ground-based remote sensing of Nitrous Oxide (N2O) over Hefei in eastern China from high resolution Fourier Transform Infra-Red (FTIR) solar spectra. We have retrieved Column-averaged Abundance of N2O () from both Near-Infrared (NIR, 4000 to 11,000 cm−1) and Mid-Infrared (MIR, 2400 to 3200 cm−1) solar spectra and inspected their agreement. Generally, NIR and MIR measurements agree well with a correlation coefficient of 0.86 and an average difference of (1.33 ± 4.05) ppbv (NIR – MIR). By correcting the bias of the two datasets, we combine the NIR and MIR measurements to investigate seasonality and inter-annual trend of over Hefei. The observed monthly mean time series of minimize in June and maximize in September, with values of (316.55 ± 12.22) ppbv and (322.05 ± 12.93) ppbv, respectively. The time series from 2015 to 2020 showed an inter-annual trend of (0.53 ± 0.10) %/year over Hefei, China. We also compared the FTIR observations with GEOS-Chem model simulations. They are in reasonable agreement with a correlation coefficient (R) of 0.71, but GEOS-Chem model underestimated the seasonality of the observations. This study can enhance current knowledge of ground-based high-resolution FTIR remote sensing of N2O in the atmosphere and contribute to generating a new reliable N2O dataset for climate change research.

Synchrotron‐based FTIR microspectroscopy of human primary retinal pigmented epithelial cells as a model for age‐related macular degeneration

AbstractPurpose: To investigate the characteristics of untreated and treated human retinal pigmented epithelial cells (hRPEs) as an ex vivo model for age‐related macular degeneration (AMD) using high resolution synchrotron radiation‐based Fourier Transform Infrared (FTIR) microspectroscopy and multivariate analysis.Methods: hRPEs obtained from cadavers were treated by autophagy ‐inducer rapamycin (Rap), and ‐inhibitor bafilomycin A1 (Baf), as well as hydrogen peroxide (H2O2) to induce oxidative stress, in an ex vivo model for studying AMD. FTIR measurements were performed at the MIRAS beamline of the ALBA Synchrotron, Barcelona, Spain.Results: The FTIR spectra consisted of several bands arising from the vibration of different groups belonging to proteins, lipids and nucleic acids, indicating the rich biochemical composition of the hRPEs. In the protein region, the amide I band of the treated groups (Rap, Baf, H2O2) was different from the control untreated group, indicating an overall protein disordering under such treatments. In the DNA region, two spectral areas appeared to be modified upon treatment, indicating different modifications of the DNA conformational changes or rearrangements attributed to the distortions of the DNA double helix in the presence of Rap, Baf or H2O2. The same treatments could also induce several modifications in the lipid spectral region, which can affect a wide range of biological processes. The H2O2 treated group showed higher prevalence for the lipid peroxidation, a process generated by the effect of several reactive oxygen species.Conclusions: The present study shows that high resolution FTIR can be used to evaluate the complete bio−/macro‐molecular spectra of hRPEs such as proteins, lipids and nucleic acids, which can be used as an ex vivo model for AMD, thus giving possibilities for developing and testing new treatment modalities.

Impact of instrumental line shape characterization on ozone monitoring by FTIR spectrometry

Abstract. Retrieving high-precision concentrations of atmospheric trace gases from FTIR (Fourier transform infrared) spectrometry requires a precise knowledge of the instrumental performance. In this context, this paper examines the impact on the ozone (O3) retrievals of several approaches used to characterize the instrumental line shape (ILS) function of ground-based FTIR spectrometers within NDACC (Network for the Detection of Atmospheric Composition Change). The analysis has been carried out at the subtropical Izaña Observatory (IZO, Spain) by using the 20-year time series of the high-resolution FTIR solar absorption spectra acquired between 1999 and 2018. The theoretical quality assessment and the comparison to independent O3 observations available at IZO (Brewer O3 total columns and electrochemical concentration cell, ECC, sondes) reveal consistent findings. The inclusion of a simultaneous retrieval of the ILS parameters in the O3 retrieval strategy allows, on the one hand, a rough instrumental characterization to be obtained and, on the other hand, the precision of the FTIR O3 products to be slightly improved. The improvement is of special relevance above the lower stratosphere, where the cross-interference between the O3 vertical distribution and the instrumental performance is more significant. However, it has been found that the simultaneous ILS retrieval leads to a misinterpretation of the O3 variations on daily and seasonal scales. Therefore, in order to ensure the independence of the O3 retrievals and the instrumental response, the optimal approach to deal with the FTIR instrumental characterization is found to be the continuous monitoring of the ILS function by means of independent observations, such as gas cell measurements.

Fourier transform infrared (FTIR) spectrum (250–3800 cm−1) of formaldoxime-13C (13CH2NOH) and rovibrational analysis of its [formula omitted] band

The Fourier transform infrared (FTIR) spectrum of formaldoxime-13C (13CH2NOH) was recorded in the 600–3800 cm−1 region with a resolution of 0.50 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared band intensities. Furthermore, the high-resolution (0.00096 cm−1) FTIR spectrum of the ν12 band of 13CH2NOH was recorded at the Australian Synchrotron in the 250–600 cm−1 region for a rovibrational analysis. A total of 1506 infrared (IR) transitions of the C-type ν12 band were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000364 cm−1 for both fits. From the rovibrational analysis, the v12 = 1 state rovibrational constants up to one sextic centrifugal distortion term were derived for the first time. The band center of the ν12 band of 13CH2NOH were found to be 397.365846(32) cm−1 in the A-reduced Hamiltonian. The ground state rovibrational constants up to one sextic term were improved with higher accuracy by fitting 1374 ground state combination differences (GSCDs) derived from the IR transitions of the ν8 and ν12 bands of 13CH2NOH, together with two previously reported microwave frequencies. Furthermore, a comparison of the experimental vibrational frequencies, IR band intensities, rovibrational constants (v12 = 1 and ground states) of 13CH2NOH and those derived from theoretical calculations at two levels of theory: B3LYP and MP2 with cc-pVTZ basis set were made. Close agreement was found for the calculated and experimental rovibrational constants of 13CH2NOH for both ground and v12 = 1 states.

Fourier transform infrared (FTIR) spectroscopy of formaldoxime (CH2NOH) in the 450–3800 cm−1 region and its [formula omitted] band

The Fourier transform infrared (FTIR) spectrum of formaldoxime (CH2NOH) was recorded in the 700–3800 cm−1 region at the Australian Synchrotron with an unapodized resolution of 0.5 cm−1 to identify its fundamental and overtone bands and to measure their relative infrared (IR) intensities in this region. The high-resolution FTIR spectrum of the ν9 band of CH2NOH was also recorded with an unapodized resolution of 0.00096 cm−1 in the 450–600 cm−1 region for a rovibrational analysis. In the analysis of the A/B-hybrid type ν9 band, a total of 2011 infrared transitions (1655b-type and 356 a-type transitions) were fitted using the Watson's A-reduced and S-reduced Hamiltonians in the Ir representation with a root-mean-square (rms) deviation of 0.000096 cm−1 and 0.000305 cm−1 respectively. From this rovibrational analysis, the v9 = 1 state rotational constants (A, B and C) and five quartic terms (ΔJ, ΔJK, ΔK, δJ, δK) were improved from previous work and three sextic terms (ΦJK, ΦKJ, ΦK) were derived for the first time. The band center of the ν9 band of CH2NOH was found to be 530.0187764(63) cm−1 and 530.018762(18) cm−1 in the A-reduced and S-reduced Hamiltonians respectively. All five quartic and three sextic (ΦJK, ΦKJ, ΦK) centrifugal distortion terms of the ground state of CH2NOH were also improved with higher accuracy. They were obtained through the fitting of 3020 ground state combination differences (GSCDs) derived from the IR transitions of the ν9, ν12 and ν10 bands of CH2NOH, together with 23 previously reported microwave frequencies. The rms deviation of this GSCD fit was 0.000498 cm−1 and 0.000519 cm−1 in the A-reduced and S-reduced Hamiltonians respectively. Additionally, rotational constants and higher order centrifugal distortion terms of the ground and v9 = 1 states were computed from theoretical anharmonic calculations at two different levels of theory, B3LYP and MP2 with the cc-pVTZ basis set, for comparison with the experimental results. The calculated and experimental rovibrational constants of CH2NOH for both ground and v9 = 1 states were in good agreement.

Surface-enhanced resonance Raman scattering of MoS2 quantum dots by coating Ag@MQDs on silver electrode with nanoscale roughness

Molybdenum disulfide quantum dots (MQDs) possess unique optical and electronic properties owing to their typical microstructures, such as two-dimensional (2D) honeycomb structure, quantum confinement, and surface passivation. However, the microstructures that have been experimentally investigated are far from being sufficient evidence for clearly understanding the electronic and optical mechanism due to the lack of effective detection methods. Here, pure MQDs were fabricated through the laser ablation of bulk MoS2 along the orientation parallel to the MoS2 layers, which is essential for surface-enhanced Raman scattering (SERS) measurement. Surface-enhanced resonance Raman scattering (SERRS) is introduced to dramatically enhance the Raman signals of MQDs by coating Ag@MQDs on a silver electrode with nanoscale roughness and highlights much more abundant Raman peaks corresponding to the MQD microstructures of the hexagonal crystalline domains, passivation electron-donating groups, defects, and disorders than those highlighted by normal Raman scattering (NRS) and resonant Raman scattering (RRS). Furthermore, owing to the adsorption of MQDs via oxygen-containing passivation groups on the silver surface, SERRS highlights more vibrations associated with passivation structures than Fourier transform infrared (FTIR) spectra that are usually applied to provide crucial evidence for the existence of passivation groups. Abundant Raman peaks derived from the defects and disorders of MQDs are also observed. Additionally, several second-order Raman peaks that are related to the hexagonal structure of MQDs can also be observed and are induced by defects, disorders, and adsorption on the silver surface. This work indicates that SERRS has advantages over high-resolution transmission electron microscopy (HRTEM), FTIR, NRS and RRS in characterizing the microstructures of MQDs.

High-resolution FTIR spectroscopy of 12C2HD3 in the 830–1110 cm−1 region: A study of the Coriolis and anharmonic interactions within the v3 = 1, v6 = 1 and v8 = 1 triad

The infrared spectrum of ethylene-d3 (12C2HD3) was measured between 830 and 1110 cm-1, covering the ν3, ν6 and ν8 bands, using a Fourier transform infrared (FTIR) spectrometer at an unapodized resolution of 0.0019 cm−1. The three upper vibrational states were found to mutually-interact through Coriolis and anharmonic resonances. A total of 2128 a- and b-type absorption lines of the ν3 band and 3107c-type lines of the ν8 band were assigned in this work. Although the ν6 band is relatively weak, 246 spectral lines were identified and included in the final fit for the rovibrational parameters of the upper vibrational states. Using a Hermitian Hamiltonian comprising Watson's-type rotational operators and off-diagonal interaction terms, three sets of rovibrational constants up to quartic terms were derived for the v3 = 1, v6 = 1 and v8 = 1 states together with thirteen interaction parameters, with a root-mean-square (rms) deviation of the fit = 0.00059 cm−1. The band centres of the ν3, ν6 and ν8 bands were determined to be 1044.260675 ± 0.000025 cm−1, 998.60182 ± 0.00060 cm−1 and 918.732573 ± 0.000019 cm−1 respectively. A set of ground state rovibrational constants of 12C2HD3 up to five quartic constants was also derived with improved precision from a simultaneous fit of 782 ground state combination differences (GSCDs) from a-type infrared transitions of the ν3 band and 1422 GSCDs from the c-type ν8 band from the present analysis, together with 377 GSCDs from the previous work on the 2ν8 band. The rms deviation of the GSCD fit was 0.00039 cm-1. The experimental spectroscopic parameters compare favourably with the quantum-chemically calculated values at the MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory.

Improved FTIR retrieval strategy for HCFC-22 (CHClF<sub>2</sub>), comparisons with in situ and satellite datasets with the support of models, and determination of its long-term trend above Jungfraujoch

Abstract. Hydrochlorofluorocarbons (HCFCs) are the first, but temporary, substitution products for the strong ozone-depleting chlorofluorocarbons (CFCs). HCFC consumption and production are currently regulated under the Montreal Protocol on Substances that Deplete the Ozone Layer and their emissions have started to stabilize or even decrease. As HCFC-22 (CHClF2) is by far the most abundant HCFC in today's atmosphere, it is crucial to continue to monitor the evolution of its atmospheric concentration. In this study, we describe an improved HCFC-22 retrieval strategy from ground-based high-resolution Fourier transform infrared (FTIR) solar spectra recorded at the high-altitude scientific station of Jungfraujoch, the Swiss Alps, 3580 m a.m.s.l. (above mean sea level). This new strategy distinguishes tropospheric and lower-stratospheric partial columns. Comparisons with independent datasets, such as the Advanced Global Atmospheric Gases Experiment (AGAGE) and the Michelson Interferometer for Passive Atmospheric Sounding (MIPAS), supported by models, such as the Belgian Assimilation System for Chemical ObErvation (BASCOE) and the Whole Atmosphere Community Climate Model (WACCM), demonstrate the validity of our tropospheric and lower-stratospheric long-term time series. A trend analysis on the datasets used here, now spanning 30 years, confirms the last decade's decline in the HCFC-22 growth rate. This updated retrieval strategy can be adapted for other ozone-depleting substances (ODSs), such as CFC-12. Measuring or retrieving ODS atmospheric concentrations is essential for scrutinizing the fulfilment of the globally ratified Montreal Protocol.

The [formula omitted] and [formula omitted] interacting bands of C2D4 by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of C2D4 in the 1443–1550 cm−1 region was recorded at an unapodized resolution of 0.0063 cm−1 to analyze its A-type ν7+ν8 band. Rovibrational constants of the (ν7=ν8=1) state of C2D4 up to five quartic terms were derived for the first time from a fit 1405 assigned infrared (IR) transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.00068 cm−1. Majority of the rotational energy levels of the (ν7=ν8=1) state of C2D4 were perturbed by the nearby (ν4=ν8=1) state by a c-type Coriolis interaction. Rovibrational analysis of the IR transitions (both perturbed and unperturbed) of the ν7+ν8 band allows for the c-type Coriolis resonance parameters, Z7,4c and w7,4c, for the ν7+ν8 and ν4+ν8 interacting bands to be determined for the first time. In addition, the band center and three rotational constants (A, B and C) of the unobserved ν4+ν8 band were also derived from the perturbed analysis of this work. The rotational constants of the ν7+ν8 and ν4+ν8 bands derived from this study were found to agree within 2.6% to the calculated values using MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory. The band centers of the ν7+ν8 and ν4+ν8 bands were determined to be 1495.894487(40) cm−1 and 1504.5065(37) cm−1 respectively. Furthermore, the band center and rotational constants of the infrared inactive ν8 band of C2D4 were derived from the present analysis of the ν7+ν8 band and that of the previously reported ν7 band of C2D4.

High-resolution multi-scan compact Fourier transform-infrared spectrometer.

The Fourier transform-infrared (FT-IR) spectrometer is a widely used high-resolution spectral characterization method in materials, chemicals, and more. However, the inverse relation between the spectral resolution and the interferometer's arm length yields a tradeoff between spectral resolution and spectrometer footprint. Here, we introduce a novel method to overcome this traditional FT-IR resolution limit. The enhanced high-resolution multi-scan compact FT-IR spectrometer we present achieves an effectively long interferogram by combining multiple short FT-IR scans. Simulation and experimental results demonstrate a significant increase in the spectral resolution of a FT-IR spectrometer by employing our interferogram stitching algorithm.

Coriolis interaction between the [formula omitted] and [formula omitted] bands of 13C2D4 by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of 13C2D4 in the 1420–1530 cm−1 region was recorded at an unapodized resolution of 0.0019 cm−1 to analyze its A-type ν7+ν8 band. Rovibrational constants of the v7=v8=1 state up to five quartic terms were derived for the first time from a fit of 1100 assigned infrared transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with an rms deviation of 0.00080 cm−1. Some of the transitions of the ν7+ν8 band were perturbed by the upper energy levels of the ν4+ν8 band by a c-type Coriolis interaction. Rovibrational analysis of the perturbed and unperturbed infrared transitions of the ν7+ν8 band allows for the c-type Coriolis resonance parameter, Z7,8c, for the ν7+ν8 and ν4+ν8 interacting bands to be determined for the first time. The band center and three rotational constants (A, B and C) of the v4=v8=1 state were also derived accurately from the perturbed analysis in this work. The rotational constants of both v7=v8=1 and v4=v8=1 states derived from this work were found to agree within 1.1% to the calculated values using MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory. The band centers of ν7+ν8 and ν4+ν8 were determined to be 1473.625489(51) cm−1 and 1488.633(11) cm−1 respectively.

The Influence of Instrumental Line Shape Degradation on the Partial Columns of O3, CO, CH4 and N2O Derived from High-Resolution FTIR Spectrometry

High resolution Fourier transform infrared (FTIR) measurement of direct sunlight does not only provide information of trace gas total columns, but also vertical distribution. Measured O3, CO, CH4, and N2O can be separated into multiple partial columns using the optimal estimation method (OEM). The retrieval of trace gas profiles is sensitive to the instrument line shape (ILS) of the FTIR spectrometer. In this paper, we present an investigation of the influence of ILS degradation on the partial column retrieval of O3, CO, CH4, and N2O. Sensitivities of the partial column, error, and degrees of freedom (DOFs) of each layer to different levels of ILS degradation for O3, CO, CH4, and N2O are estimated. We then evaluate the impact of ILS degradation on the long-term measurements. In addition, we derive the range of ILS degradation corresponding to the acceptable uncertainties of O3, CO, CH4, and N2O results. The results show that the uncertainties induced by the ILS degradation on the absolute value, error, and the DOFs of the partial column are altitude and gas species dependent. The uncertainties of the partial columns of O3 and CO are larger than those on CH4 and N2O. The stratospheric partial columns are more sensitive to the ILS degradation compared to the tropospheric part. Our result improves the understanding of the ILS degradation on the FTIR measurements, which is important for the quantification of the measurement uncertainties and minimizes the bias of the inter-comparison between different measurement platforms. This is especially useful for the validation of satellite observations, the data assimilation of chemical model simulations, and the quantification of the source/sink/trend from the FTIR measurements.

Fourier transform infrared spectroscopy of 13C2D4 in the 2000–4800 cm−1 region: Revisit of the [formula omitted] and [formula omitted] bands

A low resolution (0.5 cm−1) Fourier transform infrared (FTIR) spectrum of 13C2D4 in the 2000–4800 cm−1 region was recorded to re-analyze the two fundamental bands (ν9 and ν11) and to identify the combination bands in this region. The combination bands ν2+ν12, ν6+ν11, ν6+ν9, ν1+ν12, ν5+ν12, ν2+ν11, ν2+ν9, ν5+ν11 and ν5+ν9 were identified and their band centers (with an uncertainty of ± 0.1 cm−1) and band types were determined. In addition, the high-resolution FTIR spectrum of the fundamental ν11 band (2120–2250 cm−1) was recorded at an unapodized resolution of 0.0019 cm−1 and its infrared (IR) lines were analyzed. Rovibrational constants up to five quartic terms and band center of 2193.75943(22) cm−1 were derived with improved precision for the ν11=1 state, with an rms deviation of 0.0019 cm−1. Three rotational constants and the band center of the ν2=ν7=1 state together with the b-Coriolis resonance parameter were derived with improved precision from the study of the Coriolis interactions between the two states (ν11=1 and ν2=ν7=1). Also in this work, the FTIR spectrum of the ν9 band of 13C2D4 was measured between 2230 and 2450 cm−1 at an unapodized resolution of 0.0019 cm−1. For the first time, 2069 perturbed and unperturbed IR transitions of the ν9 band, centered at 2324.358484(46) cm−1, were fitted to obtain the a-Coriolis resonance parameter from its interaction with the ν4=ν10=ν12=1 state. The IR lines of the ν4+ν10+ν12 band were too weak for detection. Two rotational constants (A and B), the band center of the ν4+ν10+ν12 band and the a-type Coriolis resonance parameter were derived for the first time in this work. All the rotational constants A, B and C for the ν11, ν9 and ν2+ν7 bands are in close agreement with theoretically calculated values using the cc-pVQZ basis set at MP2 and B3LYP levels of theory. Ground state rovibrational constants of 13C2D4 up to three sextic terms were also derived from a fit of 3153 ground state combination differences (GSCDs) with an rms deviation of 0.00037 cm−1 from the IR transitions of the present analyses.

Re-analysis of the high-resolution FTIR spectrum of the [formula omitted] band of 13C2HD3 in the 810–1010 cm−1 region: Coriolis interactions with the [formula omitted] and [formula omitted] bands

The spectrum of the C-type ν8 band of 13C2HD3, in the region of 810 to 1010 cm−1, was recorded using a Fourier transform infrared (FTIR) spectrometer, at an unapodized resolution of 0.0019 cm−1. Improved rovibrational constants of the v8=1 state up to five quartic terms were derived from a fit of 1433 assigned unperturbed infrared transitions using Watson's A-reduced Hamiltonian in the Ir representation. For the first time, Coriolis interactions between the v8=1, v6=1 and v3=1 states were studied. A total of 828 perturbed infrared absorption lines, together with the unperturbed infrared transitions, were fitted to obtain a precise set of three rotational constants for the v6=1 state, band centers for the ν6 and ν3 bands, and two a- and b-Coriolis resonance parameters. The fit of an expanded set of ground state combination-differences derived from a larger number of perturbed and unperturbed infrared measurements in this work also yielded rotational and quartic centrifugal distortion constants of the ground state of 13C2HD3 with improved precision, with an rms deviation of 0.00040 cm−1. The experimentally-derived rotational constants of the ground and v8=1 states compared favourably with those from anharmonic calculations using the MP2/cc-pVQZ and B3LYP/cc-pVQZ levels of theory.

High-resolution FTIR spectroscopy of H13COOD: The ground state and v2 = 1 state rovibrational constants

The Fourier transform infrared (FTIR) rovibrational spectrum of the ν2 band of the formic acid isotopologue H13COOD was recorded in the 2550–2710 cm−1 region at an unapodized resolution of 0.0063 cm−1. Rovibrational constants up to three quartic terms were derived for the first time with high precision for the v2=1 state through the fitting of 626 infrared transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.0023 cm−1. The rotational energy levels of the ν2 band was found to be perturbed by a nearby 3ν7 + ν8 band. From the analysis, a- and b-Coriolis resonance parameters from the interactions of the ν2 band with 3ν7 + ν8 band were obtained for the first time. The rotational constants A and B along with the band center of the 3ν7 + ν8 band were also derived for the first time in this work. The band centers of the ν2 and 3ν7 + ν8 bands of H13COOD were determined as 2631.13155(34) cm−1 and 2596.31(19) cm−1 respectively. The ground state constants of H13COOD were determined with higher precision than previously by fitting 301 ground state combination-differences (GSCDs) from the present work and 24 previous microwave measurements with rms deviation of 0.00073 cm−1. The equilibrium state rovibrational constants up to five quartic terms were derived from theoretical anharmonic calculations at four levels of theory: MP2/cc-pVTZ, B3LYP/cc-pVTZ, MP2/cc-pVQZ and B3LYP/cc-pVQZ using the principal axis coordinate system. These calculated constants agree with the ground state constants of H13COOD derived from the current experimental GSCD combined with microwave transitions fit. In addition, all three rotational constants (A, B and C) of the ground state of H13COOD were obtained from anharmonic calculations using B3LYP and MP2 levels with the cc-pVTZ and cc-pVQZ basis sets. These rotational constants were found to agree with those derived experimentally with percentage deviations within 1.0%.

FTIR spectral imaging enhancement for teacher’s facial expressions recognition in the intelligent learning environment

Fourier transform infrared (FTIR) spectral imaging is a valuable tool for rapid identification of the real/fake human face in a single spectral image. However, it often suffers from the problems of band overlap and random noise. In this work, we have developed a spectral resolution enhancement algorithm via the contourlet transforms regularization for FTIR spectral imaging. First, we apply the contourlet transform to the observed FTIR spectrum and the ground-truth one, and compare their distributions of the contourlet coefficients. It shows that the distribution of the ground-truth spectrum is sparser than that of the observed one. Then, an infrared spectral resolution enhancement model is built to regularize the distribution of the observed FTIR spectrum by total variation regularization. Furthermore, an alternating scheme is exploited to estimate the instrument function and the latent FTIR spectrum, and it shows excellent convergence and stability. Experimental results show the effectiveness of the proposed approach in suppressing random noise and preserving spectral details in the FTIR spectral resolution enhancement problems. Thus, the proposed method leads the high-resolution FTIR spectrum as a more efficient tool for the recognition of teacher's facial expressions in the intelligent learning environment.