Mid-wave infrared liquid crystal shutter for breathalyzer applications

There exists a problem with an in situ diagnostics of contamination of ethyl alcohol in a human being exhaled air. When ethyl alcohol in a mouth blowing (in a gaseous state) exists, the characteristic CH stretch absorption bands in CH₃ and CH₂ functional groups in ethanol (CH₃CH₂OH) appear at a wavelength of λ = 3.42 μm. To investigate the presence of ethyl alcohol in exhaled human air, the light beam of λ = 3.42 μm is passing through an air sample. If one alternately measures the intensity of the investigated beam and the reference, a percentage of ethanol in the air sample can be estimated using a sensitive nondispersive infrared (NDIR) system with a stable operating flow mass detector. To eliminate a mechanical chopper and noise generating stepper motors, a photonic chopper as a liquid crystal shutter for λ = 3.42 μm has been designed. For this purpose, an innovative infrared nematic liquid crystal mixture was intentionally prepared. The working mixture was obtained by a selective removal of CH bonds and its exchange by heavier polar substituents, what ensures a lack of absorption band of CH bonds. The paper presents theory, concept and final experimental results of the infrared nematic liquid crystals mixture and the liquid crystal shutter for breathalyzer applications.     

The microwave spectrum and conformation of bromomethyl cyclopropane

The microwave spectrum of gaseous bromomethyl cyclopropane

is reported in the range 12 to 36 GHz. Lines of the ⁷⁹Br and ⁸¹Br species of cis and gauche forms are assigned and partial r₀-structures derived. The rotational constants in MHz are: gauche C₃H₅CH₂⁷⁹Br, A = 11 469.285, B = 1 374.777, C = 1 295.394; gauche C₃H₅CH₂⁸¹Br, A = 11 400.100, B = 1 364.088, C = 1 283.952; cis C₃H₅CH₂⁷⁹Br, A = 8 759.918, B = 1 597.413, C = 1 522.141; cis C₃H₅CH₂⁸¹Br, A = 8 716.552, B = 1 583.761, C = 1 509.017.     

Physical,optical and radiative properties of CaSO4–B2O3–P2O5 glasses doped with Sm3+ ions

Trivalent rare earth ions doped borosulfophosphate glasses are in high demand owing to their several unique attributes that are advantageous for applications in diverse photonic devices. Thus, Sm³⁺ ion doped calcium sulfoborophosphate glasses with composition of 25CaSO₄–30B₂O₃–(45?x)P₂O₅–xSm₂O₃ (where x?=?0.1, 0.3, 0.5, 0.7 and 1.0 mol%) were synthesized using melt-quenching technique. X-ray diffraction confirmed the amorphous nature of the prepared glass samples. Differential thermal analyses show transition peaks for melting temperature, glass transition and crystallization temperature. The glass stability is found in the range 91?°C to 116?°C which shows increased stability with addition of Sm₂O₃ concentration. The Fourier transform infrared spectral measurements carried out showed the presence of vibration bands due to PO linkage, BO_3, BO₄, PO₄, POP, OPO, SOB, and BOB unit. Glass density showed increase in value from 2.179 to 2.251?g cm^?3 with increase in Sm₂O₃ concentration. The direct, indirect band gap and Urbach energy calculated were found to be within 4.368–4.184?eV, 3.641–3.488?eV and 0.323–0.282?eV energy ranges, respectively. The absorption spectra revealed ten prominent peaks centered at 365, 400, 471, 941, 1075, 1228, 1375, 1477, 1528 and 1597?nm corresponding to ⁴D_3/2,⁶H_5/2→⁴I_11/2,⁶P_3/2, ⁶F_11/2, ⁶F_9/2, ⁶F_7/2, ⁶F_5/2, ⁶F_3/2, ⁶H_15/2 and ⁶F_1/2 transitions respectively. Photoluminescence spectra monitored at the excitation of 398?nm exhibits four emission bands positioned at 559, 596,643 and 709?nm corresponding to ⁴G_5/2→⁶H_5/2, ⁶H_7/2, ⁶H_9/2 and ⁶H_11/2 transitions respectively. The nephelauxetic parameters calculated showed good influence on the local environment within the samarium ions site and the state of the SmO bond. The Judd–Ofelt intensity parameters calculated for all glass samples revealed that Ω_6?>?Ω_4?>?Ω₂. The emission cross-section and the branching ratios values obtained for ⁴G_5/2→⁶H_7/2 transition indicate its suitability for LEDs and solid-state laser application.     

Magnetic susceptibility of liquid Na1−xSbxalloys

The magnetic susceptibility of liquid NaSb alloys was measured in a temperature range between 600°C and 1100°C. The NaSb system is supposed to exhibit, as does the CsSb system, a metal to semiconductor transition dependent upon composition. A relatively strong diamagnetic minimum of x = ?26 × 10^?6 cm³/mol was found near the composition of the stoichiometric formula Na₃Sb. This minimal susceptibility can be relatively well described with an ionic type binding model.     

Insights into the interaction kinetics between propene and NOx at moderate temperatures with experimental and modeling methods

This work aims to provide insight into the interaction of propene with NO_x from both experimental and kinetic modeling perspectives. The oxidation of propene at fuel-lean (?=0.23) condition and the oxidation of propene doped with NO_x at fuel-lean (?=0.23) and fuel-rich (?=1.35) conditions have been investigated in a laminar flow reactor at atmospheric pressure in the temperature range of 725-1250 K. Synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to achieve comprehensive, isomer-resolved identification of major products and critical nitrogenous, carbonyl and hydrocarbon intermediates. To complement the experiments, a detailed kinetic model, starting from widely used core mechanisms, was developed. Rate of production analyses and sensitivity analyses were performed to interpret the experimental observations. The results show that the promoting effects of NO_x on the oxidation reactivity of propene are initiated by the reactions of allyl radical with NO₂ at low temperature, i.e. C₃H₅A+NO₂C₃H₅O+NO. For the oxidation of the fuel-rich propene/NO_x mixture, temperature-dependent mole fraction profiles of propene, O₂ and products show several distinct regions reflecting a competition between chain propagation via C₃H₅A+NO₂C₃H₅O+NO and chain termination via C₃H₅A+NOC₃H₅NO. The formation and consumption chemistry of carbonyl and hydrocarbon intermediates in the presence of NO_x was also analyzed and discussed.     

The gas-phase structure of azetidine: Microwave spectroscopy,and electron diffraction and normal coordinate analysis

The geometric structure of azetidine has been determined by a combined analysis of electron diffraction and microwave data, implementing the results of a normal coordinate analysis. The following geometric parameters (r_z values) for the ring skeleton have been obtained: CN = 1.473 (3), CC = 1.563 (3)Å, CNC = 91.2 (0.4)° and puckering angle θ = 29.7 (1.4)°. The microwave spectra were analyzed for the ground state of the parent and N-deuterated species and for the υ = 1 and υ = 2 states of the puckering vibration of the parent species. Dipole moments and nitrogen quadrupole coupling constants were determined. The structural parameters are compared to previous experimental and theoretical results for azetidine and are discussed in context with the isoelectronic cyclobutane and oxetane.     

Nb 3d and O 1s core levels and chemical bonding in niobates

A set of available experimental data on binding energies of Nb 3d_5/2 and O 1s core levels in niobates has been observed with using energy difference (O 1sNb 3d_5/2) as a robust parameter for compound characterization. An empirical relationship between (O 1sNb 3d_5/2) values measured with XPS for Nb⁵⁺-niobates and mean chemical bond length L(NbO) has been discussed. A range of (O 1sNb 3d_5/2) values possible in Nb⁵⁺-niobates has been defined. An energy gap ∼1.4–1.8 eV is found between (O 1sNb 3d_5/2) values reasonable for Nb⁵⁺ and Nb⁴⁺ states in niobates.     

Growth and ordering of CuO chains on Ag(110) surface

Growth of CuO chains and their ordering on Ag(110) surface were monitored by scanning tunneling microscopy (STM). When Cu atoms were deposited on a (2 × 1)AgO/Ag(110) surface at room temperature, the AgO chains in the [001] direction diminished and new strings of CuO grew along the [110] direction and yield a (2 × 2) p2mg ordering. When a Ag(110) surface with coexisting AgO and CuO chains was exposed to CO at room temperature, the AgO chains were selectively reduced.     

Thermal activation and reaction of allyl alcohol on Ni(100)

The thermal chemistry of allyl alcohol (CH₂CHCH₂OH) on a Ni(100) single-crystal surface was studied by the temperature programmed desorption (TPD) and the X-ray photoelectron spectroscopy (XPS). The allyl alcohol adsorbs molecularly on the metal surface at 100 K. Intact molecular desorption from the surface occurs at temperatures around 180 K, but some molecules exhibit chemical reactivity on the surface: activation of the OH, CC, and CO bonds produces η¹(O)-allyloxy CH₂CHCH₂O_(a), η²(C, C) allyl alcohol (C_(a)H₂C_(a)HCH₂OH), and η³(C, C, O)-alkoxide (C_(a)H₂C_(a)CH₂ O_(a)) intermediates. Further thermal activation of allyl alcohol on the surface yields propylene (CH₂CHCH₃), 1-propanol (CH₃CH₂CH₂OH), propanal (CH₃CH₂CHO), and combustion and dehydrogenation products (H₂O, H₂, and CO). Propylene desorbs from the surface at temperatures of around 270 K. Hydrogenation to the η³(C, C, O)-alkoxide intermediate leads to the production of propanal which desorbs from the surface around 320 K, while hydrogenation of the η²(C, C) allyl alcohol intermediate produces 1-propanol, which desorbs at around 310 K. The co-adsorption of hydrogen atoms on the surface enhances the formation of the saturated alcohol, while co-adsorption of oxygen enhances the formation of both the saturated alcohol and the saturated aldehydes.     

Infrared diode laser spectroscopy of N212C18O2

The high-resolution infrared spectrum of N₂¹²C¹⁸O₂ has been observed in the ν₃ band (2314 cm^?1) region of ¹²C¹⁸O₂ with diode laser absorption spectroscopy of pulsed molecular beam. The geometry of N₂¹²C¹⁸O₂ is similar to N₂¹²C¹⁶O₂, a T-shaped structure with the nitrogen molecular axis pointing towards the carbon atom. The geometrical parameters of the T-shaped ground-state structure are determined as R_NcmC = 3.7285(5) Å and (90?Θ_NcmCO) = 6.85(3)°. The vibrational band origin of N₂¹²C¹⁸O₂ corresponding to the ν₃ mode of ¹²C¹⁸O₂ shows a shift of 0.52499(10) cm^?1 with respect to that of ¹²C¹⁸O₂.     

In situ upgrading of bio-oil via CaO catalyst derived from organic precursors

The fast pyrolysis of biomass with catalysts is a promising route for producing upgraded bio-oil as an alternative energy source. A CaO catalyst prepared from organic calcium compounds (Org-CaO) was first used to upgrade the pyrolysis oil of Jatropha curcas seeds in situ. Calcium d-gluconate monohydrate, calcium citrate tetrahydrate, and calcium acetate hydrate were employed as the organic precursors in this work. The results showed that Org-CaO exhibited better deoxygenation ability to produce more hydrocarbons than conventional CaO derived from Ca(OH)₂ (CHCaO). Acids accounted for 83% of the oxygenated compounds in the raw bio-oil and were almost completely removed via CaO. For bio-oil catalyzed by Org-CaO, the fraction of esters in the oxygenated compounds was only ～9%, which was 20% less than that in CHCaO bio-oil. The relative content of ketones and alcohols in Org-CaO bio-oil increased by 16% versus that in CHCaO bio-oil. Org-CaO exhibited a remarkably larger pore size and much smaller particle sizes. Thus, Org-CaO entered into the fuel through the pore channels, and this promoted the formation of chemical crosslinking points between CaO and oxygenated groups. In addition, the basicity and the amount of basic sites for Org-CaO increased versus CHCaO. Thus, the adsorption forms of oxygen-containing groups in the bio-oil on the basic sites of CaO changed: the carboxyl groups were removed from the acids and were absorbed in a stable form of unidentate carbonate on oxygen vacancies (O^2?). The stable form was bidentate carbonate on Ca²⁺–O^2?. In addition, oxygen vacancies on Org-CaO extracted more hydroxyl groups from the acids, resulting in dehydroxylation of acids to form ketones and alcohols.     

Growth and vibrational properties of MnOx thin films on Rh(111)

The growth, structures, and vibrational properties of ultrathin manganese oxide films on Rh(111) had been investigated using high-resolution electron energy loss spectroscopy (HREELS), X-ray photoelectron spectroscopy (XPS), low energy electron diffraction (LEED), low energy ion scattering spectroscopy (LEIS) and Auger electron spectroscopy (AES). MnO_x grew in a layer-by-layer fashion on the Rh(111) surface. HREELS phonon features and XPS binding energies showed that an OMnO like tri-layer formed initially. Which was stable on the Rh(111) surface with MnO_x coverage less than one monolayer. At above one monolayer, Mn₃O₄ was preferred as indicated from a four-phonon feature peaked at 13.3, 39, 68 and 83 meV in HREELS. Higher temperature oxidation and annealing were found to improve the long-range order of the MnO_x films.     

Oxygen chemisorption as a tool for atom discrimination in the SiGe termination layer

This Letter describes a novel method of employing the phenomenon of oxygen chemisorption for atom discrimination in the SiGe surface termination layer. Formation of SiO species on clean Si(100) gives rise to peaks at 7 and 10.2 eV in He I UPS and a peak at 532.3 eV in O 1s XPS. Whereas GeO species on a Ge(100) surface exhibits a single peak at 5.2 eV in He I UPS and a peak at 531.3 eV in O 1s XPS. These signature spectra of SiO and GeO species have been effectively employed for atom discrimination in the termination layer of SiGe surfaces. Upon dosing at room temperature, on a sample prepared by depositing 5ÅGe on Si(100) at 550°C, oxygen bonds with Ge atoms forming GeO, exclusively. This indicates termination entirely by Ge atoms. Oxygen adsorption at room temperature, on a sample prepared by codeposition of Ge and Si (total 5Å) onto Si(100) at 550°C, forms a mixture of SiO and GeO species suggesting a surface termination by both Ge and Si atoms.     

Nonstoichiometry of the perovskite-type solid solution La0.9Ca0.1Cr1−yAlyO3−δ

Nonstoichiometry of the perovskite-type solid solutions La_0.9Ca_0.1Cr_1−yAl_yO_3−δ was studied by high-temperature gravimetry under controlled P(O₂) atmospheres of 1–10^− 23 bar at 1073–1273 K. The observed data were described by a regular solution-like model for the randomly distributed defects of V_O¨, Cr_Cr., Ca_La,, and Al_Cr^X. With the increase in y, V_O¨ formation becomes much easier. For y > 0.8, some fraction of Ca_La, becomes surrounded only by Al_Cr^X and V_O¨ remains around such Ca_La, up to high P(O₂) to reduce the maximum oxygen content below 3.000.     

IR wavelength-selective laser desorption via OH and CH stretching modes

We present new results on wavelength-selective desorption of solid samples using the resonant interaction between the laser beam and the bulk. The experimental set-up is based on the coupling of three techniques: laser desorption in the near-infrared (IR) (2.7–4 μm) with a tunable IR optical parametric oscillator (OPO), UV multi-photon ionization, and reflectron time-of-flight mass spectrometry. The resonant character of the laser desorption process has been investigated for an ice/polycyclic aromatic hydrocarbon (PAH) mixture, by excitation of the OH and CH stretching modes. Highly preferential desorption has been evidenced, with exclusive desorption of water and PAH molecules at the OH and CH resonances, respectively. Potential analytical (e.g. selective analysis of complex samples) and technological (e.g. dry laser cleaning, DLC) applications are discussed.     

Structural characteristics of mixed oxides MOx/SiO2 affecting photocatalytic decomposition of methylene blue

A series of photocatalysts based on silica (nanoparticulate) supported titania, ceria, and ceria/zirconia were synthesized and characterized by a variety of techniques including surface area measurements, X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, surface charge density, and photocatalytic behavior toward methylene blue decomposition. Thermal treatment at 600 °C increases the anatase content of the titania based catalysts detected by XRD. Changes in the infrared spectra before and after thermal treatment indicate that at low temperature there are more SiOTi bonds than at high temperature. As these bonds break upon heating the SiO₂ and TiO₂ separate, allowing the TiO₂ anatase phase to form. This results in an increased catalytic activity for the thermally treated samples. Nearly all titania based samples exhibit a negative surface charge density at pH 7 (initial pH of photocatalytic studies) which aids adsorption of methylene blue. The crystallinity of ceria and ceria/zirconia based catalysts are in some cases limited, and in others non-existent. Even though the energy band gap (E_g) can be lower for these catalysts than for the titania based catalysts, their photocatalytic properties are inferior.     

The ground-state rotational spectrum of cyclopropyl silane

The rotational spectrum of cyclopropyl silane has been recorded in the region 9.0–35.0 GHz. Eighty-eight transitions of the ground vibrational state were measured and analyzed to give rotational constants and centrifugal distortion constants. The dipole moment was determined to be μ_a = 0.847(17)D, μ_c = 0.273(10)D, and μ_tot = 0.890(18)D. The rotational constants are consistent with a shortening of the CC bond length opposite to the silyl group. Since no splittings due to internal rotation were observed, a lower limit for the hindering potential of the internal rotation of the silyl group is V₃ ≥ 1950cal/mole.     

A density functional theory study of CF3CH2I adsorption and reaction on Ag(111)

The adsorption and reaction behaviors of CF₃CH₂I on Ag(111) were systematically studied by density functional theory (DFT) calculations. Physical adsorption of CF₃CH₂I on Ag(111) occurs due to the weak interactions between surface Ag atoms and iodine atom of CF₃CH₂I; while strong chemisorption occurs for CF₃CH₂ fragment on Ag(111). Electronic analysis indicates that the singly occupied molecular orbital (SOMO) of CF₃CH₂ strongly interacts with the surface Ag atoms. It is very interesting to find that the most stable structures of CF₃CH₂ on Ag(111) locate at the top site, instead of the hollow sites. This might be attributed to the facts that CF₃CH₂ adsorbed at the top site will maximize the sp³-type hybridization, and the possible weak interaction between the fluorine lone pair electrons of p orbitals for CF₃CH₂ and surface Ag(111) occurs, which is supported by the charge density difference (CDD) analysis with a low isosurface value. We propose that the charge density difference (CDD) analysis with a high or low isosurface value can be widely applied to analyze the strong or weak electronic interactions upon adsorption. Transition state calculations suggested that the energy barrier of CF bond rupture for CF₃CH₂I on Ag(111) (1.44 eV) is much higher than that of CI bond breakage for CF₃CH₂I (0.43 eV); and the activation energy of the CF bond dissociation for CF₃CH₂(a) is 0.67 eV.     

Dimethyl methylphosphonate decomposition on fully oxidized and partially reduced ceria thin films

The thermal decomposition of dimethyl methylphosphonate (DMMP) on crystalline ceria thin films grown on Ru(0 0 0 1) was studied by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy (XPS) and infrared absorption reflection spectroscopy (IRAS). TPD experiments show that methanol and formaldehyde desorb as the two main products at 575 K, while water, formaldehyde and CO are produced above 800 K. IRAS studies demonstrate that DMMP adsorbs via the phosphoryl oxygen at 200 K, but the PO bond converts to a bridging OPO species at 300 K. DMMP decomposition initially occurs via POCH₃ bond scission to form methyl methylphosphonate (MMP) and methyl phosphonate (MP) between 300 and 500 K; XPS and IRAS data are consistent with a methoxy intermediate on the surface at these temperatures. The more stable PCH₃ bonds remain intact up to 700 K, and the only surface intermediate at higher temperatures is believed to be PO_x. Although the presence of PO_x decreases activity for DMMP decomposition, some activity on the ceria surface remains even after 7 cycles of adsorption and reaction. The ceria films become reduced by multiple DMMP adsorption-reaction cycles, with the Ce⁺⁴ content dropping to 30% after seven cycles. Investigations of DMMP reaction on reduced ceria surfaces show that CO and H₂ are produced in addition to methanol and formaldehyde. Furthermore, DMMP decomposition activity on the reduced ceria films is almost completely inhibited after only 3 adsorption-reaction cycles. Similarities between DMMP and methanol chemistry on the ceria films suggest that methoxy is a key surface intermediate in both reactions.     

AC susceptibilities and size effect in Ln0.7(Sr,Ca)0.3MnO3 CMR manganites

The low field susceptibility versus temperature has been studied for the series of colossal magnetoresistive (CMR) manganites Ln_0.7Ca_0.3−xSr_xMnO₃ (LnPr, x = 0.10, 0.05, 0; LnNd, x = 0). The effect of the average size of the interpolated cation upon T_c is confirmed for the larger sizes (LnPr, x = 0.10, 0.05) showing a classical ferromagnetic behavior at low temperature in agreement with the neutron diffraction studies. For a smaller size of the A-site cation (LnPr or Nd, x = 0) an original behavior is observed: the _χ′(T) curves show a spin-glass-like behavior with a cusp at T_cusp, whereas the neutron diffraction data in zero magneteic field evidence a ferromagnetic component starting around T_cusp.