Mid-infrared frequency-agile dual-comb spectroscopy

\begin{wrapfigure}{p}{0pt} \includegraphics[scale=0.24]{Graph01.eps} \end{wrapfigure} We demonstrate a new approach to mid-infrared dual-comb spectroscopy. It opens up new opportunities for accurate real-time spectroscopic diagnostics and it significantly simplifies the technique of dual-comb spectroscopy. Two mid-infrared frequency combs of slightly different repetition frequencies and moderate, but rapidly tunable, spectral span are generated in the 2800-3200 cm$^{-1}$ region. The generators rely on electro-optic modulators, nonlinear fibers\footnote{G. Millot, S. Pitois, M. Yan, T. Hovannysyan, A. Bendahmane, T.W. H\"{a}nsch, N. Picqu\'{e}, Frequency-agile dual-comb spectroscopy, Nature Photonics 10, 27-30 (2016).} for spectral broadening and difference frequency generation and do not involve mode-locked lasers. Flat-top frequency combs span up to 10 cm$^{-1}$ with a comb line spacing of 100 MHz (3$\times$10$^{-3}$ cm$^{-1}$). The performance of the spectrometer without any phase-lock electronics or correction scheme is illustrated with spectra showing resolved comb lines and Doppler-limited spectra of methane. High precision on the spectroscopic parameter (line positions and intensities) determination is demonstrated for spectra measured on a millisecond time scale and it is validated with comparison with literature data

HIGH RESOLUTION SPECTRA OF THE SIMPLEST CRIEGEE INTERMEDIATE CH2OO BETWEEN 880 AND 932 cm−1

The Criegee intermediates (CI) play critical roles in atmospheric chemistry. \chem{CH_2OO} is the simplest CI and its characterization is important for investigations of reaction mechanisms and molecular structure. In this work, high-resolution spectra of the OO-stretching (\nub{6}) mode of \chem{CH_2OO} in the range of 880\textendash932 \wn have been recorded using a quantum cascade laser (QCL) system coupled with a multi-pass Herriott cell. The \chem{CH_2OO} was produced from the reaction of \chem{CH_2I} + \chem{O_2} in a flowing mixture of \chem{CH_2I_2}$/$\chem{O_2} (1/213) at 3.2 Torr upon irradiation at 248 nm with an excimer laser. The spectrum was recorded by step-scanning the QCL with a step size of ~0.0016 \wn; its wavelength was calibrated with a \chem{C_2H_4} reference cell and a germanium etalon. Over one thousand lines were assigned and used for fitting of molecular constants of \chem{CH_2OO}. Furthermore, the rotational perturbations on the high-J levels of K$_{a}$ = 3, K$_{a}$ = 6, and K$_{a}$ $\geq$ 11 were observed

Steady state analytical solutions for pumping in a fully bounded rectangular aquifer

Using the Schwartz-Christoffel conformal mapping method together with the complex variable techniques, we derive steady state analytical solutions for pumping in a rectangular aquifer with four different combinations of impermeable and constant-head boundaries. These four scenarios include: (1) one constant-head boundary and three impermeable boundaries, (2) two pairs of orthogonal impermeable and constant-head boundaries, (3) three constant-head boundaries and one impermeable boundary, and (4) four constant-head boundaries. For these scenarios, the impermeable and constant-head boundaries can be combined after applying the mapping functions, and hence only three image wells exist in the transformed plane, despite an infinite number of image wells in the real plane. The closed-form solutions reflect the advantage of the conformal mapping method, though the method is applicable for the aspect ratio of the rectangle between 1/10.9 and 10.9/1 due to the limitation in the numerical computation of the conformal transformation from a half plane onto an elongated region (i.e., so-called “crowding” phenomenon). By contrast, for an additional scenario with two parallel constant-head boundaries and two parallel impermeable boundaries, an infinite series of image wells is necessary to express the solution, since it is impossible to combine these two kinds of boundaries through the conformal transformation. The usefulness of the results derived is demonstrated by an application to pumping in a finite coastal aquifer

Analytical solutions of seawater intrusion in sloping confined and unconfined coastal aquifers

Sloping coastal aquifers in reality are ubiquitous and well documented. Steady state sharp-interface analytical solutions for describing seawater intrusion in sloping confined and unconfined coastal aquifers are developed based on the Dupuit-Forchheimer approximation. Specifically, analytical solutions based on the constant-flux inland boundary condition are derived by solving the discharge equation for the interface zone with the continuity conditions of the head and flux applied at the interface between the freshwater zone and the interface zone. Analytical solutions for the constant-head inland boundary are then obtained by developing the relationship between the inland freshwater flux and hydraulic head and combining this relationship with the solutions of the constant-flux inland boundary. It is found that for the constant-flux inland boundary, the shape of the saltwater interface is independent of the geometry of the bottom confining layer for both aquifer types, despite that the geometry of the bottom confining layer determines the location of the interface tip. This is attributed to that the hydraulic head at the interface is identical to that of the coastal boundary, so the shape of the bed below the interface is irrelevant to the interface position. Moreover, developed analytical solutions with an empirical factor on the density factor are in good agreement with the results of variable-density flow numerical modeling. Analytical solutions developed in this study provide a powerful tool for assessment of seawater intrusion in sloping coastal aquifers as well as in coastal aquifers with a known freshwater flux but an arbitrary geometry of the bottom confining layer

Application of meso-2,3-Dimercaptosuccinic Acid Self-assembled Gold Electrode for Voltammetric Determination of Copper

Fabrication and electrochemical characteristics of the meso-2,3-dimercaptosuccinic acid (DMSA) self-assembled monolayer modified gold electrode were described. The modified electrode exhibited increased sensitivity and selectivity for CuII compared to the bare gold electrode by stripping voltammetry and the peak current was proportional to the concentration of CuII in the range of 8.0 10–7 1.2 10–4 mol/L with the detection limit of 1.1 10–7 mol/L. The influence of coexistent substances was investigated and the modified electrode showed good selectivity for copper determination. The DMSA/Au electrode was applied for CuII determination in a tap water sample with satisfactory results, with the recovery in the range from 99.7 to 101.1 %

Sustainable road alignment planning in the built environment based on the MCDM-GIS method

Sustainable road planning in the cities' built-up areas strives to meet traffic demands of society within limited spaces available for construction and various constraints in the built environment considering engineering, traffic, economic, social, and environmental factors. Unlike rural areas, road planning in the built environment can be significantly influenced by the surroundings, such as existing buildings, road network, and land use, and should consider noise and air pollution impact on residents. In addition, road width and road widening are significant factors for road alignment planning. Based on the MCDM-GIS method, the least-cost wide path algorithm is employed for sustainable road alignment planning in the built environment, considering building demolition and land use, traffic congestion, noise impact, air pollution impact, and construction costs. Road width, new road construction, and existing road widening are considered simultaneously. Several methods are proposed to digitalise and parse various sustainable factors into understandable expressions for road alignment planning. Forbidden areas and road buffer areas for road widening are defined. The proposed method is implemented in road planning in Dartford, Kent County, UK. Sustainable factors with different weights can generate various road alignments from different perspectives, and road widths can significantly and locally influence road alignments

3,5-Dinitro­benzoyl chloride

The carbonyl chloride group in the title compound, C7H3ClN2O5, is disordered over two orientations with occupancies of 0.505 (5) and 0.495 (5). The mol­ecule is approximately planar, the dihedral angle between the carbonyl chloride plane and benzene ring being 9.6 (4)° in the major disorder component and 7.1 (4)° in the minor component. The nitro group at the 5-position is twisted, forming a dihedral angle of 6.7 (4)°. The crystal packing is stabilized by C—H⋯O hydrogen bonds

Mid-infrared dual-comb spectroscopy with electro-optic modulators

We demonstrate dual-comb spectroscopy based on difference frequency generation of frequency-agile near-infrared frequency combs, produced with the help of electro-optic modulators. The combs have a remarkably flat intensity distribution and their positions and line spacings can be selected freely by simply dialing a knob. We record, in the 3-micron region, Doppler-limited absorption spectra with resolved comb lines within milliseconds. Precise molecular line parameters are retrieved. Our technique holds promise for fast and sensitive time-resolved studies e.g. of trace gases

Dimethyl 2-nitro­terephthalate

In the mol­ecule of the title compound, C10H9NO6, the two ester groups and the nitro group are inclined at 9.2 (2), 123.3 (6) and 135.2 (5)°, respectively to the mean plane of the benzene ring. In the crystal structure, mol­ecules are stacked along the a axis, without any π–π inter­actions. The stacked columns are linked together by non-classical intermolecular interactions of the type C—H⋯O