High-resolution cavity ring-down spectroscopy measurements of blended H<Subscript>2</Subscript>O transitions

We probed four closely spaced rovibrational water vapor absorption transitions near =7100 cm^-1 using frequency-stabilized cavity ring-down spectroscopy. Room-temperature spectra were acquired for pure water vapor in the Doppler limit and for mixtures containing ≈6.6 μmol mol^-1 of water vapor in N₂ at total gas pressures ranging from 6.5 kPa to 53 kPa. By measuring Lamb dips for each transition, we demonstrated a resolution of 50 kHz and determined relative transition frequencies with an uncertainty <0.4 MHz over a 10 GHz range. Pressure-induced broadening, collisional narrowing coefficients of the component transitions and line areas were retrieved by fits of model line shapes to the measured spectra. Standard and advanced models were considered including those which incorporated the combined effects of collisional narrowing and speed-dependent line broadening and line shifting. By measuring water vapor concentration with a transfer standard hygrometer, we determined line intensities in terms of measured line areas with a combined relative uncertainty of 0.6%. PACS 33.20.-t; 33.70.Jg; 33.70.Fd; 42.62.Fi     

Direct detection of acetylene in air by continuous wave cavity ring-down spectroscopy

Diode laser-based continuous wave cavity ring-down spectroscopy (cw-CRDS) in the near-infrared region has been used to measure the mixing ratio of acetylene (C₂H₂) in ambient air. Detection limits of 120 parts per trillion by volume (pptv) for 20 min and 340 pptv for 70 s acquisition time were achieved without sample pre-concentration, measuring on a C₂H₂ absorption line at 6565.620 cm^?1 (～1523 nm). Several indoor and outdoor air samples were collected at different locations in the Helsinki metropolitan area and analyzed using static-cell measurements. In addition, flow measurements of indoor and outdoor air have been performed continuously over several days with a time resolution of down to one minute. Baseline acetylene levels in the range of 0.4 to 3 parts per billion by volume (ppbv), with a maximum around midday and a minimum during the night, were measured. Sudden high mixing ratios of up to 60 ppbv were observed in outdoor air during daytime on a minute time scale. In general, the indoor mixing ratios were found to be higher than those in outdoor air. The acetylene levels correlated with the ambient CO levels and with outdoor temperature.     

Ultra-sensitive ambient ammonia detection using CO<Subscript>2</Subscript>-laser-based photoacoustic spectroscopy

An ambient trace-ammonia sensor that uses resonant photoacoustic spectroscopy and a line-tunable CO₂ laser has been developed. This system achieves a 1 replicate precision of 32 parts-per-trillion (ppt) with an averaging time of 5 s and a total measurement time of 40 s. This 32-ppt precision corresponds to a minimum detectable fractional absorbance of 8.8×10^-9, a minimum detectable absorption coefficient of 9.6×10^-10 cm^-1, and a minimum path-length-normalized detectivity of 1.1×10^-8 Wcm^-1/Hz^1/2. Background interference from CO₂, H₂O, and cell-window absorption were subtracted by switching to a neighboring off-resonance laser wavelength . PACS 42.62.Fi; 82.80.Gk; 82.80.Kq     

Reactions C<Subscript>2</Subscript>H<Subscript>2</Subscript> + OH and C<Subscript>2</Subscript> + H<Subscript>2</Subscript>O: Ab initio study of the potential energy surfaces

The stationary points of the potential energy surfaces for the reactions C₂H₂ + OH and C₂ + H₂O are calculated using density functional theory and the coupled cluster method. The relative energies and geometric parameters of the stable intermediates and transition states are in good agreement with the results of independent studies. In most cases, the relative energies differ from the earlier published values by no more than 3 kcal/mol, whereas the rotational constants, by 1–2%. The mechanism of the reaction CCOH₂ → C₂ + H₂O is studied in detail. The possible sources of errors in the calculation methods are examined.     

Dielectric spectroscopy study of the new compound [C<Subscript>12</Subscript>H<Subscript>17</Subscript>N<Subscript>2</Subscript>]<Subscript>2</Subscript>CdCl<Subscript>4</Subscript>

The temperature dependence of the electrical conductivity of the compound 2,4,4-trimethyl-4,5-dihydro-3H-benzo[b] [1,4] diazepin-1-ium tetrachlorocadmiate in the different phases follows the Arrhenius law. The imaginary part of the permittivity constant is analyzed with the Cole–Cole formalism. In the temperature range 348–394 K, the activation energy of conductivity obtained from complex permittivity in regions I and II are, respectively, 1.03 and 0.33 eV, and E _m (in regions I and II are, respectively, 0.97 and 0.36 eV) obtained from the modulus spectra is close, suggesting that the ion transport is probably due to a hopping mechanism. The Kohlrausch–Williams–Watts function, j(t) = exp( - ( \fractt_\textKWW )^b ) \varphi (t) = \exp \left( { - {{\left( {\frac{t}{{{\tau_{\text{KWW}}}}}} \right)}^\beta }} \right) , and the coupling model are utilized for analyzing electric modulus at various temperatures. The decreasing of β at 373 K is due to approaching the temperatures of change in the conduction mechanism of the sample.     

Kinetics of C<Subscript>10</Subscript>H<Subscript>7</Subscript>Br Pyrolysis

The temperature and pressure-dependent rate constants for the process C₁₀H₇Br ? C₁₀H₇+Br were evaluated using the variable reaction coordinate transition state theory VRC-TST. The calculated rate constants and computational fluid dynamics (CFD) calculations were employed to estimate the pyrolysis efficiency of 2-bromonaphthalene in the resistively-heated SiC high-temperature “chemical reactor” at the temperature of about 1500 K. The observed 40% pyrolysis efficiency is reproduced by CFD calculations if the value of the calculated rate constant for the C₁₀H₇Br pyrolysis is increased by a factor of 2.     

Probing the isomer,fluorination and bond effects in C<Subscript>3</Subscript>H<Subscript>6</Subscript>, cyclo-C<Subscript>3</Subscript>H<Subscript>6</Subscript> and C<Subscript>3</Subscript>F<Subscript>6</Subscript> molecules using electron impact

We have carried out experimental and theoretical studies on electron scattering from the C₃H₆ isomers and C₃F₆ molecules and we report on total, differential as well as theoretical integral elastic cross-sections for these molecules. Vibrational excitation functions are also presented for the typical vibrational peaks in C₃H₆ and cyclo-C₃H₆ for the angle of 90^○, impact energy range of 1–16 eV and loss energies of 0.12 eV and 0.13 eV, respectively. In the cross-sections, clear differences in peak positions and magnitudes between the C₃H₆ isomers can be viewed as the isomer effect. The same is observed between C₃H₆ and C₃F₆ in a clear manifestation of the fluorination effect. The resemblance of the π^* shape resonance in the cross-sections, observed at about 2.2 eV for C₃H₆ and 3.5 eV for C₃F₆, to those in C₂H₄ and C₂F₄ clearly points to the effect of the double bond in the molecular structures for these molecules. Theoretical analysis is performed to provide rationales for the scattering dynamics.     

III. Electron-impact dissociative ionization of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

The dynamics of cold atoms in conservative optical lattices obviously depends on the geometry of the lattice. But very similar lattices may lead to deeply different dynamics. In a 2D optical lattice with a square mesh, it is expected that the coupling between the degrees of freedom leads to chaotic motions. However, in some conditions, chaos remains marginal. The aim of this paper is to understand the dynamical mechanisms inhibiting the appearance of chaos in such a case. As the quantum dynamics of a system is defined as a function of its classical dynamics – e.g. quantum chaos is defined as the quantum regime of a system whose classical dynamics is chaotic – we focus here on the dynamical regimes of classical atoms inside a well. We show that when chaos is inhibited, the motions in the two directions of space are frequency locked in most of the phase space, for most of the parameters of the lattice and atoms. This synchronization, not as strict as that of a dissipative system, is nevertheless a mechanism powerful enough to explain that chaos cannot appear in such conditions.     

II. Electron-impact dissociative excitation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact dissociative ionization of C₂ H₂⁺ and C₂ D₂⁺ to CH⁺, C⁺, C₂⁺ , H⁺, CH₂⁺ and C₂D⁺ fragments are determined for electron energies ranging from the corresponding threshold to 2.5 keV. Results obtained in a crossed beams experiment are analyzed to estimate the contribution of dissociative ionization to each fragment formation. The dissociative ionization cross sections are seen to decrease for more than an order of magnitude, from CH⁺ (5.37±0.10) × 10^-17 cm² over C⁺ (4.19± 0.16) × 10^-17 cm², C₂D⁺ (3.94±0.38) × 10^-17 cm², C₂⁺ (3.82±0.15) × 10^-17 cm² and H⁺ (3.37±0.21) × 10^-17 cm² to CH₂⁺ (2.66±0.14) × 10^-18 cm². Kinetic energy release distributions of fragment ions are also determined from the analysis of the product velocity distribution. Cross section values, threshold energies and kinetic energies are compared with the data available from the literature. Conforming to the scheme used in the study of the dissociative excitation of C₂H₂⁺ ( C₂ D₂⁺ )\left( {\rm C}_2 {\rm D}_2^+ \right), the cross-sections are presented in a format suitable for their implementation in plasma simulation codes.     

Entanglement in the linear-chain Heisenberg antiferromagnet Cu(C<Subscript>4</Subscript>H<Subscript>4</Subscript>N<Subscript>2</Subscript>)(NO<Subscript>3</Subscript>)<Subscript>2</Subscript>

Quantum correlations are generally impossible to address directly in bulk systems. Quantum measures extended only to a few number of parties can be discussed in practice. In the present work we study a cluster of spins belonging to a compound whose structure is that of a quantum magnet. We reproduce at a much smaller scale the experimental outcomes and then we study the role of quantum correlations there. A macroscopic entanglement witness has been introduced in order to reveal quantum correlations at nonzero temperatures. The critical point beyond which entanglement is zero is found at T _c = 15 K.     

I. Electron-impact ionization and dissociation of C<Subscript>2</Subscript>H<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack> and C<Subscript>2</Subscript>D<Stack><Subscript>2</Subscript><Superscript>+</Superscript></Stack>

Absolute cross-sections for electron-impact ionization and dissociation of C₂H₂⁺ and C₂D₂⁺ have been measured for electron energies ranging from the corresponding thresholds up to 2.5 keV. The animated crossed beams experiment has been used. Light as well as heavy fragment ions that are produced from the ionization and the dissociation of the target have been detected for the first time. The maximum of the cross-section for single ionization is found to be (5.56 ± 0.03)× 10^-17 cm² around 140 eV. Cross-sections for dissociation of C₂ H₂⁺ (C₂D₂⁺) to ionic products are seen to decrease for two orders of magnitude, from C₂D⁺ (12.6 ± 0.3) × 10^-17 cm² over CH⁺(9.55 ± 0.06) × 10^-17 cm², C⁺ (6.66 ± 0.05) × 10^-17 cm², C₂⁺ (5.36 ± 0.27) × 10^-17 cm², H⁺ (4.73 ± 0.29) × 10^-17 cm² and CH₂⁺ (4.56 ± 0.27) × 10^-18 cm² to H₂⁺ (5.68 ± 0.49) × 10^-19 cm². Absolute cross-sections and threshold energies have been compared with the scarce data available in the literature.     

Potential Energy Surface for Oxidation of Indenyl C<Subscript>9</Subscript>H<Subscript>7</Subscript>

Ab initio calculations were performed to obtain local energy extrema, including an effect of reagents, intermediates, and reaction products on the potential energy surface for the C₉H₇+O₂ reaction, playing a significant role in oxidation of polycyclic aromatic hydrocarbons at combustion conditions. The final products, determined as a result of the calculations are styrenyl radical C₈H₇+CO₂, ortho-vinyl phenyl radical C₈H₇+CO₂ and 1-H-inden-1-one C₉H₆O+OH, which is predicted to be the prevailing reaction product.     

Quasi-one-dimensional quantum spin liquid in the Cu(C<Subscript>4</Subscript>H<Subscript>4</Subscript>N<Subscript>2</Subscript>)(NO<Subscript>3</Subscript>)<Subscript>2</Subscript> insulator

We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-onedimensional insulator Cu(C₄H₄N₂)(NO₃)₂ (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic T–H (temperature-magnetic field) phase diagram of CuPzN that contains Landau–Fermi-liquid, crossover and non-Fermi liquid parts, thus resembling that of heavy-fermion compounds.     

Geometry of the internal dynamics of C<Subscript>2</Subscript>H<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> carbocation

Using the symmetry group chain methods, the internal dynamics of the simplest carbocation, C₂H ₃ ⁺ , is analyzed under the traditional assumptions that the equilibrium structures of the carbocation are planar and that the nonrigid motion between them is in-plane. This geometry of the internal dynamics is shown to agree with the data of the microwave spectroscopy on the splittings of rotational energy levels caused by the nonrigid motion. Previously, this statement was based on the model that violated the requirement of self-adjointness of operators of physical quantities.     

Synthesis and characterization of platinum nano sized particles by laser ablation in C<Subscript>2</Subscript>H<Subscript>6</Subscript>O<Subscript>2</Subscript> solution

Platinum nano sized particles (Pt NPs) are superior catalysts for many intentions, such as glucose sensors, cancer therapy, gas sensors, etc. Here, Pt NPs were produced by pulsed laser ablation in C₂H₆O₂ solution using Q-switched Nd:YAG laser, for the first time. Then, the influence of the laser fluence during synthesis of them was investigated; and they were characterized by UV–vis spectroscopy, TEM, FE-SEM, XRD, FT-IR, and Raman spectroscopy. The results showed that with increasing laser fluence, the mean particle size of the spherical NPs enhanced. Meanwhile, they had a polycrystalline cubic structure. Correspondingly, the plasmon peak position of generated NPs in the absorption spectra shifted from 257 to 266 nm, with a rise of laser fluence. The IR and Raman spectroscopy was used to achieve the information about the surface state of Pt NPs. We propose that the optimum adjusted laser fluence is an important factor to increase the ablation efficiency.     

Kinetics of low-temperature initiation of H<Subscript>2</Subscript>/O<Subscript>2</Subscript>/H<Subscript>2</Subscript>O mixture combustion upon the excitation of molecular vibrations in H<Subscript>2</Subscript>O molecules by laser radiation

The initiation of H₂/O₂/H₂O mixture combustion when asymmetric vibrations in H₂O molecules are excited by a resonant IR laser radiation is considered. It is shown that the vibrational excitation of the molecules gives rise to new efficient channels for the formation of chemically active O and H atoms and OH radicals. As a result, the chain mechanism of combustion in the mixtures is enhanced and, as a consequence, the induction time is cut and the ignition temperature is lowered. Even at a minor radiant energy flux delivered to the gas (E_in≈2.5 J/cm²), the ignition temperature of the stoichiometric H₂/O₂ mixture containing only 5% of H₂O may become as low as 300 K.     

Molecular structure of tris(acetylacetonato)scandium Sc(C<Subscript>5</Subscript>H<Subscript>7</Subscript>O<Subscript>2</Subscript>)<Subscript>3</Subscript>

Molecular structure of tris(acetylacetonato)scandium, Sc(C₅H₇O₂)₃, is investigated by gas-phase electron diffractometry. The main structural parameters of the molecule are evaluated. The average intemuclear distances and angles correspond to C₃ symmetry. The chief structural motif is trigonal antiprisms of six oxygen, carbon, and hydrogen atoms with a scandium atom at the center. It is found that r_g[Sc-O) = 204.1(8) pm and r_g(C−O) = 124.7(4) pm Translated fromZhurnal Struktumoi Khimii, Vol. 39, No. 4, pp. 633–639, July–August, 1998.     

EPR spectra of aerosol particles formed by pyrolysis of C<Subscript>3</Subscript>H<Subscript>8</Subscript> plus Ar and C<Subscript>3</Subscript>H<Subscript>8</Subscript> plus Fe(CO)<Subscript>5</Subscript> plus Ar mixtures in a flow reactor

The paper is devoted to electron paramagnetic resonance investigation of nanoparticles and aggregates of nanoparticles formed by pyrolysis of propane as well as a mixture of propane and iron pentacarbonyl. The measurement showed that the pyrolysis of the C₃H₈ plus Ar mixture results in the formation of a carbonaceous phase (phase I), which is quite different from that formed by the C₃H₈ plus Fe(CO)₅ plus Ar mixture (phase II). In phase I there is a strong oxygen effect for as-prepared samples; 75% of spins are accessible to the environmental gas via the interconnected system of microvoids and microchannels. In phase II there was a weak oxygen effect for the as-prepared samples. However, after exposition of phase II to air for 160 h, the properties of phase II have become about the same as that of phase I. A strong oxygen effect was observed for the air-exposed phase II. The line width for phase II increases monotonically with the iron content in the sample. This increase is probably related to the dipole-dipole interactions between the radical centers and the iron atoms distributed throughout the carbon matrix.