Thermometry of an oxy-acetylene flame using multiplex degenerate four-wave mixing of C2

Thermometry of an oxy-acetylene flame using multiplex Degenerate Four-Wave Mixing (DFWM) of C₂ is demonstrated. More than 100 rotational transitions in thed ³ _g a ³ _u (0,0) Swan band of C₂ could be recorded simultaneously by use of a pulsed, broad bandwidth modeless laser. Temperatures were inferred by fitting temperature-dependent synthetic spectra of single- or multiple-shot averaged spectra. The strength and reliability of recorded signals together with the large number of rotational lines observed suggest that multiplex DFWM is a promising technique for minor species detection and for temporally resolved temperature measurements in luminous environments. Factors influencing the accuracy and precision of single-shot thermometry using the technique are discussed.     

Detection of NO in a spark-ignition research engine using degenerate four-wave mixing

We report the first application of degenerate four-wave mixing (DFWM) to combustion diagnostics in a methane-fuelled internal combustion research engine. Combustion-generated NO in the spark-ignited engine was detected using scanning narrowband DFWM in a modified forward folded BOXCARS geometry. The resulting spectra of the X²Π-A²Σ⁺(0,0) band at 226 nm display an excellent signal-to-noise ratio. Extension of the technique to different engine operating conditions and to time-resolved multiplex DFWM is discussed. Received: 3 May 2001 / Revised version: 1 October 2001 / Published online: 29 November 2001     

The feasibility of C. W. degenerate four-wave mixing in the far-infrared to millimeter region using an artificial Kerr medium

Using the results of Rogovin, the C. W. submillimeter phase conjugate reflectivities and response times of various prototype suspensions have been calculated for the degenerate four-wave mixing geometry. Assuming realistic liquid and particle optical constants as well as realistic submillimeter laser pump powers it is demonstrated that phase conjugate reflectivities approaching or exceeding unity could be expected in the strong pump limit for a wavelength of 100 microns. For longer wavelengths phase conjugation is not practical because the grating formation time exceeds the particle fall time hence no spatial grating can be formed. However, it is shown that if the particle buoyancy could be increased, phase conjugation could proceed with high efficiency at longer wavelengths.     

Degenerate and two‐color resonant four‐wave mixing of C2− in a molecular beam environment

In this paper, we demonstrate that degenerate and two‐color resonant four‐wave mixing spectroscopy is applicable for the sensitive and selective characterization of negative ions in a molecular beam environment. Results are shown for C , which is produced by discharging a mixture of acetylene and argon prior to supersonic expansion. Substantial signal‐to‐noise ratios of ≈ 150 show that the method is generally applicable for high‐resolution optical double‐resonance spectroscopy of negative ions. A detection sensitivity for C of ≈ 10⁷ ions/cm³ is estimated. Copyright © 2010 John Wiley & Sons, Ltd.     

Atomic beam magnetic resonance investigations in the 2p 2 3 P ground multiplet of the stable carbon isotopes12C and13C

The hyperfine structure seperations Δv andg _J -factors have been measured in the 2p ^{2 3} P states of¹³C(I=1/2) and¹²C(I=0), respectively, using the atomic beam magnetic resonance method. The results are Δv(³ P ₁,¹³C)=4.200 (25) MHz, Δv(³ P ₂,¹³C)=372.593 (25) MHz,g _J (³ P ₁,¹²C)=1.501052 (13), andg _J (³ P ₂,¹²C)=1.501039 (15). After applying corrections due to perturbations by neighbouring fine structure levels one deduces the constants of the magnetic dipole interactionA(³ P ₁,¹³C)=+2.838 (17) MHz, A(³ P ₂,¹³C)=+149.055 (10) MHz. No signs of theA-factors were determined by the experiment; they follow from the known positive sign of the nuclear magnetic moment μ _I of¹³C. CombiningA(³ P ₂,¹³C) with the results of other measurements on¹¹C, yields μ _I (¹¹C)=?0.964 (1) nm.     

Characterization of hydrophobic,oxidized porous silicon layer formed by anodic etching of n+-type silicon surface in a HF:C2H5OH:HCl:H2O2:H2O electrolyte for bio-application

Porous silicon (PS) has been prepared in the dark by anodic etching of n⁺-type (111) silicon substrate in a HF:HCl:C₂H₅OH:H₂O₂:H₂O electrolyte. The processed PS layer is characterized by means of photoluminescence (PL) spectroscopy, scanning electron microscope (SEM), water contact angle (CA) measurements, Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and micro-Raman scattering. The CA of fresh PS layer is found to be ~142°. On aging at ambient conditions, the CA decreases gently to reach ~133° after 3 month, and then it is stabilized for a prolonged time of aging. The visible PL emission from the PS layer also exhibits a good stability against aging time. The FTIR and XPS measurements and analysis show that the stable aged PS layer has rather SiO₂-rich surface. The micro/nanostructure nature of the PS layer is revealed from SEM and micro-Raman results and correlated to CA results. Stable hydrophobic surface of oxidized PS layer is attractive for bio-applications. The efficiency of the produced PS layers as an entrapping template for specific immobilization of IgG2a antibody via physical absorption process is demonstrated.     

Enhancement and generation of sum squeezing in two-mode light in mixing with coherent light using a beam splitter

Recently, we showed [J. Phys. B: At. Mol. Opt. Phys. 38, 665 (2005)] that the `amplitude-squared squeezing', a non-classical feature, can be enhanced in mixing with a coherent light beam using a beam splitter. Here, we show that the sum squeezing in a two-uncorrelated-mode light beam (one mode is in Gaussian state and the other one is in coherent state), which is degenerate limit of amplitude-squared squeezing, may be generated or enhanced in mixing with a two-mode coherent light beam using a beam splitter.     

Comparisons of some molecular properties calculated with basis sets of Slater-type orbitals and floating spherical gaussian orbitals for BH3, BH4 -, B2H6, B4H4, C2H2, C2H4, C2H6, CH4, and C3H4

Some one-electron molecular properties are calculated for BH₃, BH₄ ^-, B₂H₆, B₄H₄, CH₄, C₂H₂, C₂H₄, C₂H₆, and C₃H₄. The wave functions used are constructed from minimal basis sets of STO's and FSGO's. The results obtained from the latter wave functions show that the good agreement with the STO values of the molecular energy is not always maintained with one-electron properties.     

A pulsed laser source using stimulated Raman scattering and difference frequency mixing: Remote sensing of methane in air

Mid-infrared radiation at 3.43 μm is generated by difference frequency mixing a 1.064 μm Nd:YAG laser with a methane gas Raman shifted Nd:YAG (1.064 μm) laser at 1.54 μm in KTiOAsO₄ (KTA). Using this pulsed (7 ns), moderate energy (1 mJ) source we demonstrate the optical detection of methane in air and measure an absorption coefficient of 1.2 cm⁻¹atm⁻¹. Additional source characteristics include an intrinsic wavelength stability defined by the methane Raman vibrational frequency and a moderate linewidth (1.5 cm⁻¹).     

Molecular bond formation in Na*+N2 energy transfer: Crossed beam study of atomic alignment and orientation

We report the first full analysis of collisionally induced atomic alignment and orientation for a molecular collision process. In an experiment with crossed supersonic beams of N₀ and laser excited Na(3² P _3/2) we have studied the dependence of angular and energy resolved differential quenching cross sections as a function of the linear and circular polarization of the exciting laser light. The anisotropies observed in the linear polarization data range up to 2∶1 when corrected for electron and nuclear spin relaxation. The maximum effect is found at small scattering angles and intermediate energy transfer where the cross section is also largest. The atomic alignment angle most favourable for quenching relates to the scattering angle and can be understood in a model picture in such a way that the (NaN₂)^* molecular system is formed at internuclear distances as low asR=10a ₀. The circular asymmetry is small but with significant structure and is attributed to interaction on different potential surfaces atR>10a ₀. Full analysis of the four measurable parameter is given in terms of the density matrix in a frame withz-axis perpendicular to collision plane which allows a clear understanding of the properties of atomic reflection symmetry and coherence of the scattering process.     

CO2 laser CVD of a-Si:H: in situ gas analysis and model calculations

4 and disilane Si₂H₆ induced by continuous wave CO₂ laser irradiation has been investigated under the conditions of chemical vapor deposition (CVD) of amorphous hydrogenated silicon a-Si:H. At the very position of depositing the thin film the stationary chemical composition of the processing gas is probed in situ by an effusive molecular beam which passes through a differential pumping stage into a quadrupole mass spectrometer (QMS). With SiH₄ as educt and SF₆ as a sensitizer, SiH₄ and Si₂H₆ are found in the processing gas while Si₃H₈ or higher silanes are lacking. Si₂H₆ and SF₆ lead to SiH₄, Si₂H₆, and Si₃H₈, but higher silanes are missing. The experimentally determined composition of the processing gas is semi-quantitatively reproduced by model calculations based on the assumption of stationary local equilibrium conditions and applying thermodynamic and spectroscopic data (molecular statistics). The mass balance of the processing gas entering and leaving the CVD chamber states an atomic ratio Si:H of 1:2 for the gas phase species forming the solid deposit on the reactor walls. This finding together with theoretical considerations indicates the intermediate Si₂H₄ to be the dominating gas phase species forming the a-Si:H thin films. Received: 17 July 1998/Accepted: 20 July 1998     

Variational transition state theory with multidimensional tunnelling and kinetic isotope effects in the reactions of C2H6, C2H5D and C2D6 with .CCl3 to produce CHCl3 and CDCl3

ABSTRACT

Rate constants for the reactions of C₂H₆, C₂H₅D and C₂D₆ with .CCl₃. for the production of CHCl₃ and CDCl₃ (k₁, k₂, k₃ and k₄) were computed using variational transition state theory coupled with hybrid-meta density functional theory (MPWB1K) over the temperature range of 200–2900 K. The ground-state vibrational adiabatic potential was plotted for all channels. Small- and large-curvature tunnelling were determined to include quantum effects in the calculation of rate constants. Harmonic vibrational frequencies along the reaction path were calculated in curvilinear coordinates with scaled frequencies. Anharmonicity was included in the lowest-frequency torsion. The position of formation and dissociation of bonds was specified using the variation in harmonic vibrational frequencies along the reaction path. Representative tunnelling energy and the thermally averaged transmission probability at 298 K (P(E)exp?( ? ΔE/RT)) were determined for the reactions in which tunnelling is important. The kinetic isotope effect was used to calculate the considerable contributions of tunnelling and vibration. The expressions for rate constants were determined using nonlinear least-square fitting over the temperature range of 200–2900 K.     

Surface studies by crystal current measurement of X-ray induced secondary electron emission: II. Application to molecular adsorption: CO,C2H4, O2 and H2 on Ni(100)

The adsorption of CO, C₂H₄, O₂ and H₂ on Ni(100) has been followed by measurement of the variation in X-ray induced crystal current (XCC). With the exception of CO, the Δ XCC versus exposure plots showed breaks in slope associated with changes in overlayer structure. The direction of Δ XCC was found to be opposite to the reported work function changes.     

A novel approach towards the production of luminescent silicon nanoparticles: sputtering, gas aggregation and co-deposition with H2O

Silicon clusters were produced by sputtering of a p-doped Si target and aggregation of the Si atoms in an argon gas atmosphere. The clusters were deposited in ultra high vacuum onto either (i) carbon transmission electron microscope (TEM) grids or (ii) a liquid nitrogen cooled finger on which a thick layer of ice was co-deposited during the exposure to the cluster beam. The ice layer containing the clusters was melted to form a liquid sample which showed luminescence peaking at 421 nm when excited at 307.5 nm. The luminescence is attributed to electron-hole recombination in oxygen deficient defects in the Si–SiO₂ interface region. TEM images of the nanoparticles deposited on the carbon grids show spherical particles with diameters ranging from 4 to 50 nm, flake-like structures or nanotube-like shapes. Grids with higher deposited densities reveal clusters that are agglomerated into chains, TEM images of the dried liquid sample show a network of fibres indicating that growth into fibres is further promoted when the clusters gain mobility in the melted ice.     

Electronic-excitation transfer collisions in flames-III: Cross sections for quenching and doublet mixing of Rb(52P32, 12) doublet by N2, O2, H2 and H2O

Weighted average quenching cross sections for the Rb(5²P) doublet by N₂ and H₂O were determined in flames with temperatures ranging from 1500 to 2500 K by measuring the fluorescence efficiency. The values found are $\text{(σ}{}_{\mathrm{qu}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (19±2)}\text{A}\text{?}{}^2$ and over the entire temperature range. At a temperature of 1720 K, mixing cross sections were obtained for the same doublet with N₂, H₂, O₂ and H₂O molecules. The cross sections found are: $\text{σ}{}_{21}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= (60±12)}\text{A}\text{?}{}^2$, $\text{σ}{}_{12}\text{(}{}^2\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{→}{}^2\text{P}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}\text{)}{}_{\mathrm{<mtext>N</mtext><mtext>2</mtext>}}\text{= 99±20)}\text{A}\text{?}{}^2$; , $\text{(σ}{}_{21}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 30}\text{A}\text{?}{}_2$, $\text{(σ}{}_{12}\text{)}{}_{\mathrm{<mtext>H</mtext><mtext>2</mtext>}}\text{> 50}\text{A}\text{?}{}^2\text{;}$, . The ratios σ₁₂/σ₂₁ were measured independently and were found to agree with the detailed- balance condition within 3 per cent. A critical comparison of the flame values with previous literature data on N₂-cross sections shows that both mixing and quenching cross sections are temperature dependent in the range from 300 to 2500 K.     

Finite-field calculations of molecular polarizabilities using field-induced polarization functions: second- and third-order perturbation correlation corrections to the coupled Hartree-Fock polarizability of H2O

Ordinary Rayleigh-Schrödinger perturbation theory with Møller-Plesset (RSMP) partitioning is used to calculate second- and third-order correlation corrections to the CHF polarizability and dipole moment of the water molecule by a finite-field procedure. [2/1] Padé approximants are found to be useful in accelerating the convergence of the property perturbation expansions. Field-induced polarization functions suitable for polarizability calculations are determined. The average polarizability calculated, neglecting vibrational averaging, with Dunning's (9s5p/4s-4s2p/2s) contracted GTO basis set augmented by field-induced 1s1p2d/1p polarization functions is within 3 per cent of the experimental result. Correlation corrections to the dipole moment and polarizability of the water molecule calculated by the finite-field RSMP and single + double excitation CI(SDCI) methods for the same basis set are found to be in close agreement. The RSMP approach has the advantages of being size-consistent and of being capable of greater efficiency than the SCDI method. Comparative calculations carried out using Epstein-Nesbet partitioning show that through third order RSEN correlation perturbation expansions for the dipole moment and polarizability are less rapidly convergent than RSMP expansions. However, reasonable accord with RSMP results can be achieved by using [2/1] Padé approximants to accelerate the convergence of RSEN energy perturbation expansions. The convergence of RSMP property correlation expansions based on the zeroth-order uncoupled-Hartree-Fock (UCHF) and coupled-Hartree-Fock (CHF) approximations are compared through third order. Whereas the CHF + RSMP expansions are for practical purposes fully converged, the UCHF + RSMP expansions are not adequately converged.     

The adsorption of NO on an oxygen pre-covered Pt(1 1 1) surface: in situ high-resolution XPS combined with molecular beam studies

Adsorption of NO on a Pt(1 1 1) surface pre-covered with a p(2 × 2) atomic oxygen layer has been studied in situ by high-resolution X-ray photoelectron spectroscopy and temperature-programmed XPS using third-generation synchrotron radiation at BESSY II, Berlin, combined with molecular beam techniques and ex situ by low energy electron diffraction and temperature-programmed desorption. O 1s XP spectra reveal that an ordered p(2 × 2)-O layer dramatically changes the adsorption behavior of NO as compared to the clean surface. The atomic oxygen occupies fcc hollow sites, and therefore blocks NO adsorption on these sites, which are energetically preferred on clean Pt(1 1 1). As a consequence, NO populates on-top sites at low coverage. At 110 K for higher coverages, NO can additionally adsorb on hcp hollow sites, thereby inducing a shift of the O 1s binding energy of atomic oxygen towards lower energies by about 0.25 eV. The bond strength of the hcp hollow NO species to the substrate is weakened by the presence of atomic oxygen. A sharp p(2 × 2) LEED pattern is observed for NO adsorption on the oxygen pre-covered surface, up to saturation coverage. The total saturation coverage of NO on Pt(1 1 1) pre-covered with varying amounts of oxygen (below 0.25 ML) decreases linearly with the coverage of oxygen. The initial sticking coefficient of NO is reduced from 0.96 on clean Pt(1 1 1) to 0.88 on a p(2 × 2) oxygen pre-covered surface.     

Neutron emission in interactions of 1H, 2H, 4He, and 12C nuclei with lead nuclei at 1–2 GeV per nucleon

The double differential cross sections for neutron production that were measured by the time-of-flight method for interactions of 2-GeV p and d, 4-GeV ⁴He, and 24-GeV ¹²C with Pb nuclei are discussed. In the phenomenological model of four moving sources, the neutron energy distribution shape at emission angles above 30° is well reproduced with the temperature parameters for all sources that are almost independent of the type and the energy of incident nuclei. Using the developed model, we estimate the mean neutron multiplicity and the energy removed by neutron emission.     

Experimental determination of the nu5 cis-bending vibrational frequency and Renner-Teller structure in ground state (X2Piu) C2H2+ using laser induced reactions

The spectrum of the nu(5) cis-bending vibration of ground state (X(2)Pi(u)) C(2)H(2)(+) has been recorded applying the method of laser induced reactions in a low-temperature 22-pole ion trap. It is obtained by counting the number of products of the reaction C(2)H(2)(+) (v(5) = 1) + H(2)--> C(2)H(3)(+) + H as a function of the laser wavelength. The vibronic transitions Delta-Pi and Sigma-Pi with their corresponding spin-orbit and Renner-Teller substructure have been observed. Using a perturbative analysis, the vibrational frequency has been determined to omega(5) = (710 +/- 4) cm(-1) and the Renner-Teller parameter epsilon(5) is on the order of 3 x 10(-2).