High-resolution Fourier Transform Infrared Spectroscopy Research Articles

Combined direct-sun ultraviolet and infrared spectroscopies at Popocatépetl volcano (Mexico)

Volcanic plume composition is strongly influenced by both changes in magmatic systems and plume-atmosphere interactions. Understanding the degassing mechanisms controlling the type of volcanic activity implies deciphering the contributions of magmatic gases reaching the surface and their posterior chemical transformations in contact with the atmosphere. Remote sensing techniques based on direct solar absorption spectroscopy provide valuable information about most of the emitted magmatic gases but also on gas species formed and converted within the plumes. In this study, we explore the procedures, performances and benefits of combining two direct solar absorption techniques, high resolution Fourier Transform Infrared Spectroscopy (FTIR) and Ultraviolet Differential Optical Absorption Spectroscopy (UV-DOAS), to observe the composition changes in the Popocatépetl’s plume with high temporal resolution. The SO2 vertical columns obtained from three instruments (DOAS, high resolution FTIR and Pandora) were found similar (median difference <12%) after their intercalibration. We combined them to determine with high temporal resolution the different hydrogen halide and halogen species to sulfur ratios (HF/SO2, BrO/SO2, HCl/SO2, SiF4/SO2, detection limit of HBr/SO2) and HCl/BrO in the Popocatépetl’s plume over a 2.5-years period (2017 to mid-2019). BrO/SO2, BrO/HCl, and HCl/SO2 ratios were found in the range of (0.63 ± 0.06 to 1.14 ± 0.20) × 10−4, (2.6 ± 0.5 to 6.9 ± 2.6) × 10−4, and 0.08 ± 0.01 to 0.21 ± 0.01 respectively, while the SiF4/SO2 and HF/SO2 ratios were found fairly constant at (1.56 ± 0.25) × 10−3 and 0.049 ± 0.001. We especially focused on the full growth/destruction cycle of the most voluminous lava dome of the period that took place between February and April 2019. A decrease of the HCl/SO2 ratio was observed with the decrease of the extrusive activity. Furthermore, the short-term variability of BrO/SO2 is measured for the first time at Popocatépetl volcano together with HCl/SO2, revealing different behaviors with respect to the volcanic activity. More generally, providing such temporally resolved and near-real-time time series of both primary and secondary volcanic gaseous species is critical for the management of volcanic emergencies, as well as for the understanding of the volcanic degassing processes and their impact on the atmospheric chemistry.

Retrieval of atmospheric CFC-11 and CFC-12 from high-resolution FTIR observations at Hefei and comparisons with other independent datasets

Abstract. Synthetic halogenated organic chlorofluorocarbons (CFCs) play an important role in stratospheric ozone depletion and contribute significantly to the greenhouse effect. In this work, the mid-infrared solar spectra measured by ground-based high-resolution Fourier transform infrared spectroscopy (FTIR) were used to retrieve atmospheric CFC-11 (CCl3F) and CFC-12 (CCl2F2) at Hefei, China. The CFC-11 columns observed from January 2017 to December 2020 and CFC-12 columns from September 2015 to December 2020 show a similar annual decreasing trend and seasonal cycle, with an annual rate of -0.47±0.06 % yr−1 and -0.68±0.03 % yr−1, respectively. So the decline rate of CFC-11 is significantly lower than that of CFC-12. CFC-11 total columns were higher in summer, and CFC-12 total columns were higher in summer and autumn. Both CFC-11 and CFC-12 total columns reached the lowest in spring. Further, FTIR data of NDACC (Network for the Detection of Atmospheric Composition Change) candidate station Hefei were compared with the ACE-FTS (Atmospheric Chemistry Experiment Fourier transform spectrometer) satellite data, WACCM (Whole Atmosphere Community Climate Model) data, and the data from other NDACC-IRWG (InfraRed Working Group) stations (St. Petersburg, Jungfraujoch, and Réunion). The mean relative difference between the vertical profiles observed by FTIR and ACE-FTS is -5.6±3.3 % and 4.8±0.9 % for CFC-11 and CFC-12 for an altitude of 5.5 to 17.5 km, respectively. The results demonstrate that our FTIR data agree relatively well with the ACE-FTS satellite data. The annual decreasing rate of CFC-11 measured from ACE-FTS and calculated by WACCM is -1.15±0.22 % yr−1 and -1.68±0.18 % yr−1, respectively. The interannual decreasing rates of atmospheric CFC-11 obtained from ACE-FTS and WACCM data are higher than that from FTIR observations. Also, the annual decreasing rate of CFC-12 from ACE-FTS and WACCM is -0.85±0.15 % yr−1 and -0.81±0.05 % yr−1, respectively, close to the corresponding values from the FTIR measurements. The total columns of CFC-11 and CFC-12 at the Hefei and St. Petersburg stations are significantly higher than those at the Jungfraujoch and Réunion (Maïdo) stations, and the two values reached the maximum in local summer or autumn and the minimum in local spring or winter at the four stations. The seasonal variability at the three stations in the Northern Hemisphere is higher than that at the station in the Southern Hemisphere.

Retrieval of vertical profiles and tropospheric CO2 columns based on high-resolution FTIR over Hefei, China.

High-resolution solar absorption spectra, observed by ground-based Fourier Transform Infrared spectroscopy (FTIR), are used to retrieve vertical profiles and partial or total column concentrations of many trace gases. In this study, we present the tropospheric CO2 columns retrieved by mid-infrared solar spectra over Hefei, China. To reduce the influence of stratospheric CO2 cross-dependencies on tropospheric CO2, an a posteriori optimization method based on a simple matrix multiplication is used to correct the tropospheric CO2 profiles and columns. The corrected tropospheric CO2 time series show an obvious annual increase and seasonal variation. The tropospheric CO2 annual increase rate is 2.71 ± 0.36 ppm yr-1, with the annual peak value in January, and CO2 decreases to a minimum in August. Further, the corrected tropospheric CO2 from GEOS-Chem simulations are in good agreement with the coincident FTIR data, with a correlation coefficient between GEOS-chem model and FTS of 0.89. The annual increase rate of XCO2 observed from near-infrared solar absorption spectra is in good agreement with the tropospheric CO2 but the annual seasonal amplitude of XCO2 is only about 1/3 of dry-air averaged mole fractions (DMF) of tropospheric CO2. This is mostly attributed to the seasonal variation of CO2 being mainly dominated by sources near the surface.

Detection of atmosphere CCl<sub>2</sub>F<sub>2</sub> spatio-temporal variations by ground-based high resolution Fourier transform infrared spectroscopy

Atmospheric dichlorodifluoromethane (CCl<sub>2</sub>F<sub>2</sub>, CFC-12), as a synthetic chemical agent, is a main stratospheric ozone-depleting substance in atmosphere. Studies of the detection techniques and the temporal and spatial distribution of CFC-12 have great significance in understanding the variation trend of regional CFCs and their influence on stratospheric ozone. In this study, the method of retrieving the vertical profile and total column for CFC-12 is studied based on ground-based high-resolution Fourier transform infrared spectroscopy (FTIR). The spectral window for CFC-12 retrieval is selected as 922.5–923.6 cm<sup>–1</sup>, where the interfering gases are H<sub>2</sub>O, O<sub>3</sub>, and CO<sub>2</sub>. The result of error analysis shows that the average total error is 1.27%, including the systematic error 0.76% and random error 1.02%. The vertical profiles and total columns of atmospheric CFC-12 in Hefei during the period from 2017 to 2020 were retrieved based on the optimal estimation algorithm. The vertical profiles of CFC-12 show that the concentration of atmospheric CFC-12 is high in the troposphere and low stratosphere at the altitude of 0–20 km, and then decreases, very low at height above 40 km. The total column average kernel of retrieved CFC-12 profiles is higher at 15–20 km, and the typical signal degree of freedom of CFC-12 is 1.217. Moreover, the long-term total columns of atmosphere CFC-12 observed show obvious seasonal variation in Hefei. Total columns of atmosphere CFC-12 are higher in summer and lower in winter and early spring. The maximum monthly concentration of CFC-12 is about 1.13 × 10<sup>16</sup> mol·cm<sup>–2</sup> in July, and the minimum monthly concentration is 1.00 × 10<sup>16</sup> mol·cm<sup>–2</sup> in March. Also, the annual average total columns of atmospheric CFC-12 decreased slightly from 2017 to 2020, with an increasing rate of –0.68%. This reflects the effect of China's implementation of CFCs control ban policy. Furthermore, in order to verify the accuracy of ground-based FTIR observation, we compare our ground-based observation data with ACE-FTS/ SCISAT satellite version 4.1 level 2 data. There are 16 pairs of matching points between satellite observation and ground observation data, and the correlation coefficient is 0.73 for two CFC-12 partial columns at the height of 16–28 km, showing good agreement between ground-based FTIR data and satellite data. The long-term observations demonstrate the accuracy and reliability of ground-based high-resolution FTIR technology for detecting the vertical distribution and seasonal variation of atmosphere CFC-12.

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.

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.

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.

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%.

Application of high resolution NMR (1H and 13C) and FTIR spectroscopy for characterization of light and heavy crude oils

High-resolution nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopy experiments were applied to obtain detailed information on the hydrocarbon chemistry of three light and three heavy crude oils. Quantitative fractions of aromatic molecules and functional groups constituting oil hydrocarbons were determined by 13C NMR spectroscopy and comparative analysis of the oil samples with different viscosity, origin and preliminary treatment. SARA composition and some important information about aromaticity, oxidation behavior, branching, aliphaticity and sulfurization of studied oil samples were obtained. Integral characteristics of high-resolution NMR and FTIR spectra have a great potential to study the structure and characterization of light and heavy crude oils, which could substitute present traditional fractionation procedures. Relationships between spectroscopic parameters obtained by high-resolution NMR and FTIR spectroscopy methods and crude oil compositions can be useful for fast prediction of crude oil properties due to different type of treatment, including thermal methods for enhanced oil recovery. Also quantitative proportions of functional groups obtained by NMR and spectral indices obtained by FTIR can be one of the criteria for developing fingerprint approach.

The ν2 band of formic acid-d1 (HCOOD) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν2 band of formic acid-d1 (HCOOD) were recorded at an unapodized resolution of 0.0063 cm−1 in the 2540–2710 cm−1 region. In this work, 416 unperturbed absorption lines of the dominantly b-type ν2 band were identified and assigned for the first time. Rovibrational constants up to three quartic terms were derived with good precision for the v2=1 state through the fitting of the 416 unperturbed infrared transitions using the Watson’s A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.0011 cm−1. A total of 458 infrared (IR) transitions of the ν2 band were found to be perturbed by the transitions of a nearby band identified to be 3ν7+ν8. Finally, a total of 874 unperturbed and perturbed transitions of the ν2 band were analyzed to obtain the a- and b-Coriolis resonance parameters from its interaction with the 3ν7+ν8 band with an rms deviation of 0.0016 cm−1. The rotational constant B and the band center of the 3ν7+ν8 band (which is too weak for detection) were derived for the first time in this work. The band centers of the ν2 and 3ν7+ν8 bands of HCOOD were determined as 2631.63835 ± 0.00017 cm−1 and 2601.13 ± 0.14 cm−1 respectively.

First analysis of the hybrid A/B-type 2ν8 band of C2HD3 and the Coriolis interactions with the ν3 + ν4 band by high-resolution FTIR spectroscopy

Using a Fourier transform infrared (FTIR) spectrometer, the spectrum of the 2ν8 band of ethylene-d3 (C2HD3) was measured between 1745 to 1905 cm−1 at an unapodized resolution of 0.0063 cm−1. For the first time, 1664 perturbed and unperturbed a- and b-type absorption lines of the band were recorded, assigned and fitted using the Watson's A-reduced Hamiltonian in the Ir representation to derive rovibrational constants up to four quartic terms for the v8 = 2 state. Three rotational constants of the v3 = v4 = 1 state were also derived for the first time in this work from the analysis of the a- and b-Coriolis resonances with the v8 = 2 state, together with a set of resonance parameters. The root-mean-square (rms) deviation of the FTIR fit was 0.0010 cm−1. The band centers of the 2ν8 and ν3 + ν4 bands were determined to be 1831.457508 ± 0.000071 cm−1 and 1812.629 ± 0.022 cm−1, respectively. A set of ground state rovibrational constants of C2HD3 up to five quartic constants was also derived with improved precision from a simultaneous fit of 377 ground state combination differences (GSCDs) from a-type infrared transitions of the present analysis and 906 GSCDs from the previous work on the C-type ν8 band, with an rms deviation of 0.00043 cm−1. The transition dipole moment ratio μaμb was found to be 2.194 ± 0.072.

Comparative SIFT-MS, GC–MS and FTIR analysis of methane fuel produced in biogas stations and in artificial photosynthesis over acidic anatase TiO2 and montmorillonite

The era of fossil fuels is slowly nearing its inevitable end and the urgency of alternative energy sources basic research, exploration and testing becomes ever more important. Storage and alternative production of energy from fuels, such as methane, represents one of the many alternative approaches. Natural gas containing methane represents a powerful source of energy producing large volume of greenhouse gases. However, methane can be also produced in closed, CO2-neutral cycles. In our study, we compare detailed chemical composition of CH4 fuel produced in two different processes: Classical production of biogas in a rendering station, industrial wastewater treatment station and landfill gas station together with novel approach of artificial photosynthesis from CO2 over acidic anatase TiO2 in experimental apparatus developed in our laboratory. The analysis of CH4 fuel produced in these processes is important. Trace gaseous traces can be for example corrosive or toxic, low quality of the mixture suppresses effectivity of energy production, etc. In this analysis, we present a combination of two methods: High resolution Fourier transform infrared spectroscopy (HR-FTIR) suitable for the main component analysis; and the complementary extremely sensitive method of Selected Ion Flow Tube Mass Spectrometry (SIFT-MS) and gas chromatography (GC–MS), which are in turn best suited for trace analysis. The combination of these methods provides more information than any single of them would be able to and promises a new possible analytical approach to fuel and gaseous mixture analysis.

The ν8 band of C2HD3 by high-resolution synchrotron FTIR spectroscopy: Coriolis interactions between the v8 = 1 and v6 = 1 states

The synchrotron Fourier transform infrared (FTIR) spectrum of the ν8 band of ethylene-d3 (C2HD3) was measured at an unapodized resolution of 0.00096cm−1 from 830 to 1010cm−1. Rovibrational constants up to five quartic terms were derived with improved precision for the v8=1 state through the fitting of 1566 unperturbed infrared transitions using the Watson's A-reduced Hamiltonian in the Ir representation with a root-mean-square (rms) deviation of 0.00044cm−1. For the first time, 446 perturbed IR transitions of the ν8 band were fitted together with the 1566 unperturbed infrared transitions to obtain the a- and b-Coriolis resonance parameters from its interaction with the v6=1 state, with an rms deviation of 0.00039cm−1. The IR lines of the ν6 band were too weak for detection. Three rotational constants, a quartic constant and band center of the v6=1 state were also derived for the first time in this work. Ground state rovibrational constants of C2HD3 up to five quartic constants were also derived from a fit of 906 ground state combination differences with an rms deviation of 0.00030cm−1 from infrared transitions of the present analysis. The ground state rotational constants are in close agreement with theoretically calculated values using the cc-pVTZ basis set at CCSD(T), MP2 and B3LYP levels of theory. Alpha constants determined from the rotational constants of the v8=1 state derived from the perturbed IR fit compared favourably with those from anharmonic calculations.

Researching the Nature of Fire at 1.5 Mya on the Site of FxJj20 AB, Koobi Fora, Kenya, Using High-Resolution Spatial Analysis and FTIR Spectrometry

Some scholars explain the major anatomical characteristics that differentiate Homo erectus from its predecessor, Homo habilis, as the result of Homo erectus being adapted to use fire for cooking and other tasks. However, many scholars contend that the evidence of fire in Homo erectus sites is very scant and is not convincingly anthropogenic. This study presents a methodology to evaluate the evidence of fire associated with the 1.5-million-year-old Homo erectus site FxJj20 AB, Koobi Fora, Kenya. The evidence is in the form of thermally altered lithics, soil aggregates, and bone fragments identified using visual inspection and Fourier transform infrared spectroscopy (FTIR). We conducted high-resolution excavation focused on the recovery and high-resolution mapping of large and small finds (<2 cm). ArcGIS spatial analysis and soil micromorphology were used to assess whether the evidence of fire at the site has a natural or anthropogenic origin. Preliminary results indicate that the spatial pattern of heated and unheated archaeological material is not inconsistent with prehistoric anthropogenic fire features found in archaeological sites of Europe and West Asia.

The 2ν2 bands of H212CO and H213CO by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) absorption spectra of the 2ν2 overtone bands of formaldehyde H212CO and its isotopologue H213CO were recorded at an unapodized resolution of 0.0063cm−1 in the 3300–3540cm−1 region. Upper state (v2=2) rovibrational up to two sextic centrifugal distortion constants were accurately determined for both H212CO and H213CO. A total of 533 unperturbed infrared transitions of H212CO and 466 unperturbed infrared transitions of H212CO were assigned and fitted with rms deviations of 0.0012cm−1 and 0.00084cm−1 respectively using Watson’sA-reduced Hamiltonian in the Ir representation. Analysis of new transitions for H212CO measured in this work yielded upper state constants with greater accuracy than previously reported. The infrared transitions of the 2ν2 band of H213CO were measured for the first time. The band center of the A-type 2ν2 band of H212CO was found to be 3471.71403±0.00012cm−1 and that of H213CO was 3396.628983±0.000083cm−1. Furthermore, the newly assigned high-resolution infrared lines of the 2ν2 bands in the 3300–3540cm−1 region can be useful in detecting the H212CO and H213CO molecules in this IR region.

Rovibrational constants of the ground state and v8 = 1 state of 13C2HD3 by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the c-type ν8 band of 13C2HD3 was recorded for the first time at a unapodized resolution of 0.0063cm−1 in the wavenumber region of 830–1000cm−1. Through the fitting of a total of 1057 assigned infrared transitions using Watson’s A-reduced Hamiltonian in the Ir representation, rovibrational constants for the upper state (v8=1) up to five quartic centrifugal distortion terms were derived for the first time with a root-mean-square (rms) deviation of 0.00073cm−1. The band center of ν8 of 13C2HD3 was found to be 913.011021(55)cm−1. Ground state rovibrational constants up to five quartic terms of 13C2HD3 were also determined from a fit of 453 ground state combination-differences from the present infrared measurements with an rms deviation of 0.00072cm−1 for the first time. The uncertainty of the measured infrared lines was estimated to be ±0.0012cm−1. From the ground state rotational constants, the inertial defect of 13C2HD3 was calculated to be 0.06973(16)uÅ2, showing the high planarity of the molecule.

High-resolution FTIR spectroscopy of ethylene-d3 (C2HD3): Rovibrational constants for the ground state and the v8 = 1 state

The Fourier transform infrared (FTIR) spectrum of the v8 band of ethylene-d3 (C2HD3) was recorded with a unapodized resolution of 0.0063cm−1 in the wavenumber region of 830–1000cm−1. Improved rovibrational constants for the upper state (v8=1) up to five quartic centrifugal distortion terms were derived by assigning and fitting a total of 1249 infrared transitions using Watson’s A-reduced Hamiltonian in the Ir representation. The root-mean-square (rms) deviation of the fit was 0.00062cm−1, close to the accuracy (1/10th of a linewidth) of the measurements of the line positions of ±0.0007cm−1. The ground state rovibrational constants of C2HD3 were also determined with higher accuracy than previously reported from a fit of 568 combination-differences from the present infrared measurements with an rms deviation of 0.00038cm−1, using Watson’s A-reduced Hamiltonian. The calculated inertial defect is 0.069489(69)μÅ2. The C-type v8 band of C2HD3 was determined to be centered at 918.731925(40) cm−1. The ground state constants of C2HD3 derived from the experimental GSCD fits were in reasonable agreement with the equilibrium state constants derived from theoretical calculations using the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and CCSD(T)/cc-pVTZ levels of theory.

Rovibrational constants of the ground and ν12 = 1 states of C2D4 by high-resolution synchrotron FTIR spectroscopy

The Fourier transform infrared (FTIR) absorption spectrum of the ν12 fundamental band of ethylene-d4 (C2D4) was recorded in the 1000–1150cm−1 region with a resolution of 0.00096cm−1 using the THz/far-infrared beamline of the Australian Synchrotron. Upper state (ν12=1) rovibrational constants consisting of three rotational constants and up to five quartic constants were improved by assigning and fitting 3950 rovibrational transitions using Watson’s A-reduced and S-reduced Hamiltonians in the Ir representation. The band centres of the unperturbed A-type ν12 band are found to be 1076.984958(14) cm−1 and 1076.984813(14) cm−1 for A-reduced and S-reduced Hamiltonians respectively. The present analysis, covering a wider wavenumber range and higher J and Kc values (up to 58) than previous studies, yielded upper state constants including the band centre which are more accurate than previously reported. The rms deviation of the upper state (ν12=1) fit is 0.00040cm−1 in the A-reduction and 0.00041cm−1 in the S-reduction. Improved ground state rovibrational constants were also determined from the fit of 3151 ground state combination differences (GSCD) from the presently-assigned transitions of the ν12 band of C2D4 using Watson’s A-reduced and S-reduced Hamiltonians in the Ir representation. The rms deviation of the GSCD fit is 0.00036cm−1 in the A-reduction and 0.00035cm−1 in the S-reduction. The ground state constants of C2D4 derived from the experimental GSCD fit are in good agreement with those from theoretical calculations using the B3LYP/cc-pVTZ, MP2/cc-pVTZ, and CSSD/cc-pVTZ levels, up to five quartic constants.

Coriolis interaction of the ν2 + ν12 band with ν2 + 2ν10 of cis-C2H2D2 by high resolution FTIR spectroscopy

The high resolution Fourier transform infrared (FTIR) absorption spectrum of the ν2+ν12 band of cis-C2H2D2 was recorded in the frequency range of 2515–2960cm−1 with an unapodized resolution of 0.0063cm−1. This band was perturbed through c-type Coriolis interaction by the unobserved ν2+2ν10 band approximately 19cm−1 below ν2+ν12. A total of 751 unperturbed and perturbed infrared transitions of ν2+ν12 were assigned and fitted using Watson’s A-reduced Hamiltonian in the Ir representation with the inclusion of c-type Coriolis terms to give 11 rovibrational constants for the upper state (ν2=1, ν12=1) with improved accuracy. The ν2+ν12A-type band is centred at 2898.8975±0.0004cm−1. From the Coriolis interaction analysis between the ν2+ν12 and ν2+2ν10 bands of cis-C2H2D2, a higher order K-dependent c-type Coriolis coupling constant between the two bands was derived for the first time. Furthermore, rotational constants for the ν2+2ν10 band of cis-C2H2D2 centred at 2880.17±0.06cm−1 were also determined.

Analysis of the Coriolis interaction between ν6 and ν4 bands of ethylene-cis-d2(cis-C2H2D2) by high-resolution FTIR spectroscopy

The Fourier transform infrared (FTIR) spectrum of the ν6 band of ethylene-cis-d2(cis-C2H2D2) was recorded with a unapodized resolution of 0.0063cm−1 in the 990–1100cm−1 region. A total of 609 transitions were assigned to this band centred at 1039.7682±0.0003cm−1. The ν6 band was found to be coupled to the ν4 band by a-type Coriolis resonance. Both perturbed and unperturbed transitions were assigned and fitted to give eight rovibrational constants with high accuracy for the v6=1 state with a standard deviation of 0.00097cm−1 using a Watson’s A-reduced Hamiltonian in the Ir representation. From a rovibrational analysis of the Coriolis interaction between the ν6 band and non-infrared active ν4 band of cis-C2H2D2, the band centre of ν4 at 984.9±0.2cm−1 was derived. Furthermore, the second-order a-type Coriolis coupling constant between the two bands was obtained for the first time.