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Transformation of the measured signal from the time scale (s(t)) to the frequency scale (s(˜ ν)) based on two calibration lines at the frequency˜νfrequency˜ frequency˜ν 1 and˜νand˜ and˜ν 2 , assuming a constant spacing of the etalon peaks ("Eichpunkte" are calibration points).
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We report high resolution infrared spectra in the CF stretching fundamental ranges of trifluoromethylacetylene (CF3−C≡C-H, 3,3,3-trifluoropropyne) and of tetrafluoromethane (CF4, R14, PCF-14, Halocarbon14). For the experiments a diode laser setup combined with a supersonic jet expansion is described, achieving approximate rotational temperatures be...
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... positions of the etalon peaks are fitted as a function of time to a polynomial of order m. This allows the transformation of the measured spectra from a time scale (s(t)) to a scale of etalon peak positions (s(n)) as can be seen from Figure 5. The spectrum from the calibration gas is then used for the transformation of the signal from the n-scale of the etalon peaks (s(n)) to the absolute frequency scale (s(˜ ν)). ...
Citations
... Quack (2022): Highresolution spectroscopic measurements of cold samples in supersonic beams using a QCL dualcomb spectrometer*, Molecular Physics, ...
... Comparing the observed width to the less than 5·10 -5 cm −1 uncertainty of the width measurement reported in Ref. 38, the observed line width is likely dominated by the remaining Doppler broadening in the skimmed molecular beam. The resolution is further confirmed by Figure 5 showing the isolated R(0) line in the ν 3 band of CF 4 : this is a single line without fine structure by theory [42,55], as for CH 4 [30], and which has a FWHM of 0.00062 cm −1 which would correspond to a "Doppler temperature" of 40 K for this line. ...
... As we did not use a separate calibration gas, we have calibrated f CEO and f rep of the first step by minimising the deviation between our measurement and tabulated values [53]. These transitions have been previously measured independently [42,55,56]. While the resolution in the previous studies was not as good as that in the present work, this has little effect on the wavenumber accuracy, as the R(0) and P(1) lines are unsplit lines in a range relatively free from congestion at the lowest temperature. ...
Optical frequency-comb spectroscopy has proven a very useful tool for high-resolution molecular spectroscopy. Frequency combs based on quantum-cascade lasers (QCL) offer the possibility to easily explore the mid-infrared spectral range (4 µm to 12 µm), but are characterised by large repetition frequencies (∼ 10 GHz) which make them seemingly unsuitable for high-resolution spectroscopy. Here, we present techniques to overcome this limitation. We have employed the combined advantages of high temporal and high spectral resolution to measure the infrared (IR) spectra of CF4 and CHCl2F in pulsed, skimmed supersonic beams. The low rotational temperature of the beams and the narrow expansion cone after the skimmer enabled the recording of spectra of cold samples with high resolution. The spectra cover the range from 1200 cm⁻¹ to 1290 cm⁻¹ and the narrowest lines have a full width at half maximum of 15 MHz, limited by the Doppler effect. The results demonstrate the potential of QCL dual-comb spectroscopy for broadband (> 60 cm⁻¹) acquisition of spectra at high spectral (better than 5·10⁻⁴ cm⁻¹, 15 MHz) and temporal (better than 4 µs) resolution and high sensitivity in the mid-infrared range. The power of the new technology is demonstrated by comparison with previous results for these molecules obtained by FTIR and diode laser spectroscopy.
Nowadays, organic pollutants have been major concerns in many fields. Production of functional materials based on renewable and sustainable resources for organic pollutants detection and removal was of much interest. Herein, multi-functional nanocomposite films based on cellulose nanocrystals (CNCs) with high optical haze, organic pollutant detection and emulsion separation capabilities, have been successfully fabricated based on hydrophobically-modified CNCs suspensions by 2-dodecen-1-succinic anhydride (DDSA) followed by radical polymerization with tridecafluorooctyl (TFMA). The suspensions displayed satisfying oil-in-water emulsion stabilization capabilities and the vacuum-dried films showed birefringence, high transparency, and optical haze (~85 %), due to the ordered arrangements of cellulose nanocrystals. The organic pollutant can be detected through the iridescent colors disappearing by Polarizing Optical Microscope observation. In addition of improved mechanical strength for application (27 MPa) and high contact angle of 131.6°, the hydrophobic films performed as high separation efficiency as >90 % of emulsion, due to the successfully grafting of hydrophobic molecules on the surface of CNCs. Thus, the surface modification for CNCs provide a facile approach of emulsification, pollutants detection and separation properties, which would widen the application potentials of renewable cellulosic resources in fields of environmental protection, engineering control and petroleum industry.
