Large Amplitude Torsions In Nitrotoluene Isomers Studied By Rotational Spectroscopy And Quantum Chemistry Calculations

The monitoring of gas phase mononitrotoluenes is crucial for defence, civil security and environmental interests since they are used as taggant for TNT detection. Rotational spectra of the three isomers of nitrotoluene have been recorded at low and room temperatures using a supersonic jet Fourier Transform microwave (MW) spectrometer and a millimeter-wave frequency multiplier chain, respectively. Supported by quantum chemistry calculations, the spectral analysis of pure rotation lines in the vibrational ground state has allowed to characterise the rotational energy, the hyperfine structure due to the $^{14}$N nucleus and the internal rotation splittings arising from the methyl group. An anisotropic internal rotation of coupled -CH$_3$ and -NO$_2$ torsional motions was identified for the ortho isomer by quantum chemistry calculations and discussed from the results of its MW analysis. The study of the internal rotation splittings in the spectra of three NT isomers allowed to characterise the internal rotation potentials of the methyl group and to compare them with other mono-substituted toluene derivatives in order to study the isomeric influence on the internal rotation barrier. \footnote{Roucou \it{et al.}, CHEMPHYSCHEM, \bf{21}(22), 2523-2538, (2020).}$^,$ \footnote{Roucou \it{et al.}, CHEMPHYSCHEM, \bf{19}, 1056-1067, (2018).

INFRARED CROSS-SECTIONS OF NITRO-DERIVATIVE VAPORS: NEW SPECTROSCOPIC SIGNATURES OF EXPLOSIVE TAGGANTS AND DEGRADATION PRODUCTS

Classical explosives such as RDX or TNT exhibit a very low vapor pressure at room temperature and their detection in air requires very sensitive techniques with levels usually better than 1 ppb. To overcome this difficulty, it is not the explosive itself which is detected, but another compound more volatile present in the explosive. footnote{J. C. Oxley, J. L. Smith, W. Luo, J. Brady, Prop. Explos. Pyrotec. 34 (2009) 539�543} This volatile compound can exist naturally in the explosive due to the manufacturing process. For example, in the case of DiNitroToluene (DNT), the molecule is a degradation product of TNT and is required for its manufacture. Ortho-Mononitrotoluene (2-NT) and para-mononitrotoluene (4-NT) can be also used as detection taggants for explosive detection. In this study, using the exceptional properties of the SOLEIL synchrotron source, and adapted multipass-cells, gas phase Far-IR rovibrational spectra of different isomers of mononitrotoluene and dinitrotoluene have been investigated. Room temperature Far-IR cross-sections of the 3 isomer forms of mononitrotoluene have been determined for the lowest frequency vibrational bands located below 700 wn.footnote{A. Cuisset, S. Gruet, O. Pirali, G. Mouret, Spectrochimica Acta Part A, 132 (2014) 838-845.} Cross sections and their temperature dependences have been also measured in the Mid-IR using conventional FTIR spectroscopy probing the nitro-derivatives vapors in a heated multipass-cell

Chirped Pulse Spectrometer Operating at 200 GHz

The combination of electronic sources operating at high frequencies and modern microwave instrumentation has enabled the recent development of chirped-pulse spectrometers for the millimetre and THz bands. This type of instrument can operate at high resolution which is particularly suited to gas phase rotational spectroscopy. The construction of a chirped pulse spectrometer operating at 200 GHz is described in detail while attention is paid to the phase stability and the data accumulation over many cycles. Validation using carbonyl sulphide has allowed the detection limit of the instrument to be established as function of the accumulation. A large number of OCS transitions were identified using a 10 GHz chirped pulse and include the 6 most abundant isotopologues, the weakest line corresponding to the fundamental R(17) transition of 16 O 13 C 33 S with a line strength of 4.3 x 10-26 cm-1 /(molec.cm-2). The linearity of the system response for different degrees of data accumulation and transition line strength was confirmed over 4 orders of magnitudes. A simple analysis of the time domain data was demonstrated to provide the line broadening coefficient without the need for conversion by a Fourier transform. Finally, the pulse duration is discussed and optimal values are given for both Doppler limited and collisional regimes

Terahertz gas phase spectroscopy using a high finesse Fabry-P\'erot cavity

The achievable instrument sensitivity is a critical parameter for the continued development of THz applications. Techniques such as Cavity-Enhanced Techniques and Cavity Ring Down Spectroscopy have not yet been employed at THz frequency due to the difficulties to construct a high finesse Fabry-P\'erot cavity. Here, we describe such a THz resonator based on a low-loss oversized corrugated waveguide with highly reflective photonic mirrors obtaining a finesse above 3000 around 620 GHz. These components enable a Fabry-Perot THz Absorption Spectrometer with an equivalent interaction length of one kilometer giving access to line intensities as low as 10-27cm- 1/(molecule/cm2) with a S/N ratio of 3. In addition, the intracavity optical power have allowed the Lamb-Dip effect to be studied with a low-power emitter, an absolute frequency accuracy better than 5 kHz can be easily obtained providing an additional solution for rotational spectroscopy.Comment: 7 pages, 4 figure

Le Corbusier: Architecture as a project of the world approach to a philosophy of architecture

La arquitectura moderna como un producto humano, ayudado por la técnica, da respuesta a las necesidades humanas en el proceso de habitar el mundo. El punto central es la revisión de un “proyecto de mundo” que para algunos maquinizó el problema del habitar y para otros apostó por la esencia antropológica que subyace a la necesidad de dar expresión material a un mejor mundo humano habitable. Este trabajo no procurará entonces hacer una “reivindicación” de Le Corbusier, pues a cada momento histórico le corresponden diversas respuestas a través de los productos humanos que dan cuenta de condiciones particulares de las culturas; se trata más bien de hacer una “reinterpretación” del proyecto de mundo que se gestó con el movimiento moderno de la arquitectura y, particularmente, con Le CorbusierThis article is a result of the reflection around the modern architecture as a human product than, supported by technical, gives answers to the human needs in the process of living in the world. The point is the search and reinterpretation of a “world project” that has been considered the “machining” of the world inhabit by some, and, for others, has been understood as a an movement that opted for the anthropological essence behind the need to give material expression to the human inhabit. This paper does not seek to make a “claim” to rescue Le Corbusier, as I am aware that each historical period has different answers by human products that account for conditions in the cultures, which clearly would not make sense to emulate; rather what I tried to make a “reinterpretation” of the proposed world was conceived with the modern movement in architecture and, particularly, with Le Corbusie

Analysis of self-broadened pure rotational and rovibrational lines of methyl chloride at room temperature

International audienceRovibrational absorption spectra of methyl chloride in the spectral region between 2800 and 3200 cm 1 were recorded with a high-resolution Fourier spectrometer. A multispectrum fitting procedure was used to analyze 527 transitions of the ν1 band and to retrieve the self-broadening coefficients for various J- and K-values with an estimated accuracy around 8%. Pure rotational transitions of CH3Cl in the submillimeter/terahertz region (0.2-1.4 THz) were also investigated using two complementary techniques of frequency-multiplication and continuous-wave photomixing. 43 pure rotational self-broadening coefficients were extracted with the accuracy between 3 and 5%. The whole set of measured values was used to model the J- and K-rotational dependences of the self-broadening coefficients by second-order polynomials. In addition, semi-classical calculations were performed, based on the real symmetric-top geometry of the active molecule, an intermolecular potential model including not only the dominant electrostatic but also the short-range forces, as well as on an exact classical treatment of the relative translational motion of the colliding partners. Comparison of all experimental and theoretical results shows similar rotational dependences and no significant vibrational dependence, so that extrapolations to other spectral regions should be straightforward

Chemical and physical properties of meadowfoam seed oil and extra virgin olive oil: focus on vibrational spectroscopy

In food industry, vegetable oils are commonly used as functional ingredients. Cold pressed oils containing fatty acids show a variety of chemical properties, which are mainly dependent on the saturation of fatty acids. In this study, we have analyzed meadowfoam seed oil (MSO), obtained from seeds of Limnanthes alba, and extra virgin olive oil (EVO). Firstly, the fatty acids composition, denoted as Cox value, was determined for the oils that are considered as the most stable. The Cox value for MSO reached 0.032, while that for EVO was 1.780. We have also determined the content of fatty acids in both of the oils using gas chromatography, while the use of mid-infrared (MIR) and near-infrared (NIR) spectroscopy allowed us to assign bands corresponding to the vibrations present in the tested functional groups. Significant differences in the shape and intensity of some bands were observed due to different content of unsaturated fatty acids. Vibrational spectroscopy methods confirmed the presence of long chain fatty acids in MSO.This work was supported through the projects M-ERA-NET/0004/2015-PAIRED and UIDB/04469/2020 (strategic fund)granted by the Portuguese Science and Technology Foun-dation, Ministry of Science and Education (FCT/MEC),through national funds and cofinanced byFEDER, under the Partnership Agreement PT2020. -e authors also acknowledge the support of the research project Nutraceuticacome supporto nutrizionale nel paziente oncologico, CUP:B83D18000140007.info:eu-repo/semantics/publishedVersio

Recent Developments of an Opto-Electronic THz Spectrometer for High-Resolution Spectroscopy

A review is provided of sources and detectors that can be employed in the THz range before the description of an opto-electronic source of monochromatic THz radiation. The realized spectrometer has been applied to gas phase spectroscopy. Air-broadening coefficients of HCN are determined and the insensitivity of this technique to aerosols is demonstrated by the analysis of cigarette smoke. A multiple pass sample cell has been used to obtain a sensitivity improvement allowing transitions of the volatile organic compounds to be observed. A solution to the frequency metrology is presented and promises to yield accurate molecular line center measurements