Fast-flow System Research Articles

1 kHz Oscillation of short-pulse CO2 laser pumped by longitudinal discharge without pre-ionization

Commonly, a gas laser pumped by a pulsed discharge requires a pre-ionization system to form a uniform discharge at a high repetition rate like 1 kHz. In this paper, however, a longitudinally excited CO2 laser without any pre-ionization system operated at a repetition rate of 1 kHz. The discharge tube was made of an alumina ceramic tube with an inner diameter of 8 mm, an outer diameter of 16 mm and a length of 80 cm, and two metallic electrodes attached to the two ends of the tube, and did not have a pre-ionization system or a fast gas flow system. The CO2 laser produced short pulses with a spike pulse width of 200 ns, a pulse tail length of 150 μs, a spike pulse to pulse tail energy ratio of 1:112, a laser energy of 35.2 mJ, and a circular Gaussian-like beam at a repetition rate of 1 kHz, a CO2/N2/He gas mixing ratio of 1:1:5, a gas pressure of 4.6 kPa and an input energy of 738 mJ to the circuit generating fast, high-voltage pulses. The dependence of the laser energy on the repetition rate, the CO2/N2/He gas mixing ratio, and the input energy was investigated.

Longitudinally excited short-pulse CO2 laser with large discharge tube without preionization

A longitudinally excited CO2 laser with a large discharge tube having an inner diameter of 16 mm and a length of 80 cm produced short laser pulses with an energy of 38.1 mJ at a repetition rate of 700 Hz. The CO2 laser did not have a preionization system or a fast gas flow system. The dependence of the laser output and discharge voltage on the repetition rate, the gas pressure and the structure of the discharge tube in 1:1:4 and 1:1:2 mixtures of CO2/N2/He gas was investigated. At a repetition rate of 300 Hz or more, the laser energy decreased as the repetition rate increased. The 1:1:4 mixture of CO2/N2/He gas produced a higher laser energy than the 1:1:2 mixture of CO2/N2/He gas. At a repetition rate of 300 Hz or less, the laser beam profile was doughnut-shaped. At a repetition rate of 400 Hz or more, the center of the laser profile had a high energy. At a high repetition rate, the fast discharge may have collected in the center of the discharge tube. Moreover, an increase in the repetition rate decreased the discharge formation time and the energy of a pulse tail part of the laser pulse waveform.

Disproportionation Channel of the Self-reaction of Hydroxyl Radical, OH + OH → H2O + O, Revisited.

The rate constant of the disproportionation channel 1a of the self-reaction of hydroxyl radicals OH + OH → H2O + O (1a) was measured at ambient temperature as well as over an extended temperature range to resolve the discrepancy between the IUPAC recommended value (k1a = 1.48 × 10-12 cm3 molecule-1 s-1, discharge flow system, Bedjanian et al. J. Phys. Chem. A 1999, 103, 7017) and a factor of ca. 1.8 higher value by pulsed laser photolysis (2.7 × 10-12 cm3 molecule-1 s-1, Bahng et al. J. Phys. Chem. A 2007, 111, 3850, and 2.52 × 10-12 cm3 molecule-1 s-1, Altinay et al. J. Phys. Chem. A 2014, 118, 38). To resolve this discrepancy, the rate constant of the title reaction was remeasured in three laboratories using two different experimental techniques, namely, laser-pulsed photolysis-transient UV absorption and fast discharge flow system coupled with mass spectrometry. Two different precursors were used to generate OH radicals in the laser-pulsed photolysis experiments. The experiments confirmed the low value of the rate constant at ambient temperature (k1a = (1.4 ± 0.2) × 10-12 cm3 molecule-1 s-1 at 295 K) as well as the V-shaped temperature dependence, negative at low temperatures and positive at high temperatures, with a turning point at 427 K: k1a = 8.38 × 10-14 × (T/300)1.99 × exp(855/T) cm3 molecule-1 s-1 (220-950 K). Recommended expression over the 220-2384 K temperature range: k1a = 2.68 × 10-14 × (T/300)2.75 × exp(1165/T) cm3 molecule-1 s-1 (220-2384 K).

FTIR spectra of NaTe and KTe and ab initio calculations of the electronic structure of these molecules

Gas phase emission spectra of the hitherto unknown radicals NaTe and KTe have been measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which tellurium vapor in argon carrier gas was passed through a microwave discharge and mixed with sodium or potassium vapor in an observation tube. Excitation of the radicals mostly occurred by near-resonant E-E energy exchange from added metastable oxygen O2(a1Δg). Like for the previously studied LiTe molecule, for both radicals two systems of blue-degraded bands were measured in the range 4500–8500 cm−1. They were assigned to the transitions A2Σ+(A1/2) → X12Π3/2(X13/2) and A2Σ+(A1/2) → X22Π 1/2(X21/2). For all four subsystems vibrational analyses were performed which yielded ground state splittings of 2265.39(13) cm−1 (NaTe) and 1544.19(11) cm−1 (KTe) as well as A2Σ+ state energies of 7935.98(9) cm−1 (NaTe) and 6404.71(11) cm−1 (KTe) and vibrational constants of the X13/2, X21/2 and A1/2 states of both molecules. The 0-0 bands of both sub-transitions of NaTe were measured at high spectral resolution and rotationally analyzed.In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential curves for the low-lying states of NaTe and KTe and also electric dipole transition moments connecting them.

Storage dynamics, hydrological connectivity and flux ages in a karst catchment: conceptual modelling using stable isotopes

Abstract. We developed a new tracer-aided hydrological model that disaggregates cockpit karst terrain into the two dominant landscape units of hillslopes and depressions (with fast and slow flow systems). The new model was calibrated by using high temporal resolution hydrometric and isotope data in the outflow of Chenqi catchment in Guizhou Province of south-western China. The model could track hourly water and isotope fluxes through each landscape unit and estimate the associated storage and water age dynamics. From the model results we inferred that the fast flow reservoir in the depression had the smallest water storage and the slow flow reservoir the largest, with the hillslope intermediate. The estimated mean ages of water draining the hillslope unit, and the fast and slow flow reservoirs during the study period, were 137, 326 and 493 days, respectively. Distinct seasonal variability in hydroclimatic conditions and associated water storage dynamics (captured by the model) were the main drivers of non-stationary hydrological connectivity between the hillslope and depression. During the dry season, slow flow in the depression contributes the largest proportion (78.4 %) of flow to the underground stream draining the catchment, resulting in weak hydrological connectivity between the hillslope and depression. During the wet period, with the resulting rapid increase in storage, the hillslope unit contributes the largest proportion (57.5 %) of flow to the underground stream due to the strong hydrological connectivity between the hillslope and depression. Meanwhile, the tracer-aided model can be used to identify the sources of uncertainty in the model results. Our analysis showed that the model uncertainty of the hydrological variables in the different units relies on their connectivity with the outlet when the calibration target uses only the outlet information. The model uncertainty was much lower for the “newer” water from the fast flow system in the depression and flow from the hillslope unit during the wet season and higher for “older” water from the slow flow system in the depression. This suggests that to constrain model parameters further, increased high-resolution hydrometric and tracer data on the internal dynamics of systems (e.g. groundwater responses during low flow periods) could be used in calibration.

Limit Energy Theorem for Gas Flow Systems

The paper presents a review of research dealing with the limit energy theorem for fast gas flow systems (FGFS’s) [19, 21, 23, 24, 38] where no mechanical work is performed. FGFS’s include gas-discharge lasers and plasmatrons, chemical gas reactors, vortex tubes, acoustic systems, various gas mixing devices, astrophysical objects, etc. The analysis shows that these flow systems do not belong to the Carnot class. In contrast to the Carnot cycle efficiency, the efficiency of energy conversion in FGFS’s depends on the properties of the working medium, and the conventional FGFS cycle is essentially irreversible. For the chosen class of FGFS’s, the theorem yields a more strictly formulated second law of thermodynamics. Implications of the theorem for various fields of physics and engineering are discussed.

Theoretical and experimental study of the electronic states and spectra of LiSb

Gas phase emission spectra of the hitherto unknown free radical LiSb were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which antimony vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. A number of blue-degraded bands observed in the range 6200–7800 cm−1 are assigned to transitions from four excited states A21, A30+, A40− and a2 to the X10+ and/or X21 components of the X3Σ− ground state. The 0–0 bands of six transitions were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses have yielded the spectroscopic parameters of all six states.In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential energy curves and spectroscopic constants for the low-lying states of LiSb as well as electric-dipole transition moments and radiative lifetimes.

Catchment‐scale conceptual modelling of water and solute transport in the dual flow system of the karst critical zone

AbstractHydrological and hydrochemical processes in the critical zone of karst environments are controlled by the fracture‐conduit network. Modelling hydrological and hydrochemical dynamics in such heterogeneous hydrogeological settings remains a research challenge. In this study, water and solute transport in the dual flow system of the karst critical zone were investigated in a 73.5‐km2 catchment in southwest China. We developed a dual reservoir conceptual run‐off model combined with an autoregressive and moving average model with algorithms to assess dissolution rates in the “fast flow” and “slow flow” systems. This model was applied to 3 catchments with typical karst critical zone architectures, to show how flow exchange between fracture and conduit networks changes in relation to catchment storage dynamics. The flux of bidirectional water and solute exchange between the fissure and conduit system increases from the headwaters to the outfall due to the large area of the developed conduits and low hydraulic gradient in the lower catchment. Rainfall amounts have a significant influence on partitioning the relative proportions of flow and solutes derived from different sources reaching the underground outlet. The effect of rainfall on catchment function is modulated by the structure of the karst critical zone (e.g., epikarst and sinkholes). Thin epikarst and well‐developed sinkholes in the headwaters divert more surface water (younger water) into the underground channel network, leading to a higher fraction of rainfall recharge into the fast flow system and total outflow. Also, the contribution of carbonate weathering to mass export is also higher in the headwaters due to the infiltration of younger water with low solute concentrations through sinkholes.

Theoretical and experimental study of the electronic states and spectra of KBi and KSb

Gas phase emission spectra of the hitherto unknown free radicals KBi and KSb were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth or antimony vapor in argon carrier gas was passed through a microwave discharge and mixed with potassium vapor in an observation tube. For KBi, two systems of blue-degraded bands observed in the range 5800–7700cm−1 are assigned to the transitions A3Π (A20+)→X3Σ−(X10+, X21). Nine bands of the A20+→X10+ and three bands of the A20+→X21 system were measured at high spectral resolution and rotationally analysed. The rotational and vibrational analyses yielded the spectroscopic parameters of the X10+, X21, and A20+ states. For KSb, in the range of the sensitive Ge detector, only one sequence of bands was measured near 6880cm−1. By analogy with the previously observed spectra of NaSb and NaAs these bands were identified to be the Δv=0 sequence of the a2→X21 transition of KSb. Some very weak bands observed at low resolution in the range 3800–5200cm−1 are assigned to the transitions A3Π (A21)→X3Σ −(X10+, X21).To aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain potential energy curves for the low-lying states of KBi and KSb, vibrational constants, equilibrium internuclear distances, and also electric dipole transition moments connecting the states.

Experimental and theoretical study of the electronic states and spectra of NaAs

Gas-phase emission spectra of the hitherto unknown free radical NaAs were measured in the NIR region with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which arsenic vapor in argon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Seven transitions from all five Ω components of the low-lying A3Π and a1Δ excited states (A12, A21, A30+, A40−, a2) to the X10+ and/or X21 components of the X3Σ− ground state have been observed and analysed. With the help of parallel relativistic configuration interaction calculations all observed spectral features could be assigned and analyzed.

Experimental and theoretical study of the electronic states and spectra of SbNa

Gas-phase emission spectra of the hitherto unknown free radical SbNa were measured in the NIR region with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which antimony vapor in argon or neon carrier gas was passed through a microwave discharge and mixed with sodium vapor in an observation tube. Seven transitions from five low-lying excited states A12, A21, A30+, A40−, and B2 to the X10+ and/or X21 components of the X3Σ− ground state have been observed and analyzed.In parallel to the experiments, relativistic configuration interaction calculations of potential energy curves, vibrational constants, bond lengths, transition moments and radiative lifetimes were carried out to aid in the analysis of the experimental data.

Electronic states and spectra of BiH

Emission spectra of bismuth monohydride (BiH) radicals excited by energy transfer from O2(a1Δg) or NF(a1Δ) or by a DC discharge in a mixture of bismuth vapor and hydrogen in a fast-flow system were studied in the wavenumber range from 4000 to 25000cm−1 with a Fourier-transform spectrometer. The X21→X10+ transition between the spin components of the X3Σ− ground state was remeasured at high spectral resolution and signal/noise. Six bands of the Δv=0 and +1 sequences near 4950 and 6600cm−1 have been observed. The low-J lines of these bands are split into up to 10hfs components due to magnetic hyperfine structure splitting of the X21 levels. In addition to the previously observed electric dipole lines, weak magnetic dipole lines show up in the Δv=0 but not in the Δv=+1 bands. The intensities of the Δv=+1 bands are about a factor of 10 higher than expected from Franck–Condon factors indicating that the electric dipole transition moment μX2–X1 shows a strong dependence on internuclear distance. Near 5450cm−1, the 0-0 and 1-1 bands of the transition a2→X21 from the hitherto unknown first excited state a1Δ(a2) to the upper component of the ground state have been observed. The lines in these bands show the magnetic hfs splitting of both the a2 and X21 states. In the visible range near 21300 and 16300cm−1, the 0-0 and 1-1 bands of the b0+→X10+ system and the 0-0 band of the b0+→X21 transition likewise have been measured at high resolution. The lines of the latter band also show the hfs splitting of the X21 state. Least-squares fits have yielded rotational and vibrational constants of the X10+, X21, a2, and b0+ states as well as hfs parameters of the X21 and a2 states and the electronic energy of the hitherto unknown a1Δ(a2) level.

Experimental and theoretical study of the electronic states and spectra of BiLi

Gas phase emission spectra of the hitherto unknown free radical BiLi were measured in the NIR range with a Fourier-transform spectrometer. The emissions were observed from a fast-flow system in which bismuth vapor in argon carrier gas was passed through a microwave discharge and mixed with lithium vapor in an observation tube. Two systems of blue-degraded bands observed in the range 6900–9800cm−1 are assigned to the transitions A3Π(A20+)→X3Σ−(X10+, X21). The Δv=0, +1, and −1 sequences of both systems were measured at high spectral resolution. Rotational and vibrational analyses of 12 bands have yielded the spectroscopic parameters of the X10+, X21, and A20+ states including a hfs splitting parameter of the X21 state.In order to aid in the analysis of the experimental data, a series of relativistic configuration interaction calculations has been carried out to obtain spectroscopic parameters and potential curves for the low-lying states of BiLi and also electric dipole transition moments connecting them.

Near-infrared emission spectra of TeS, TeSe and Te2

Emission spectra of the radicals TeS, TeSe and Te2 in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The molecules were generated in a fast-flow system by reacting microwave-discharged mixtures of Tex, Sx, and/or Sex vapour and Ar carrier gas and excited by energy transfer and energy pooling processes in collisions with metastable oxygen O2(a1Δg). The b1Σ+(b0+)→X3Σ−(X10+,X21) electric dipole transitions of TeS and TeSe and the b1Σ+g(b0+g)→X3Σ−g(X21g) magnetic dipole transition of Te2 were measured at medium and high spectral resolution. A very weak emission at 3356cm−1 observed in the spectrum of TeSe was identified to be the 0–0 band of the hitherto unknown a1Δ(a2)→X3Σ−(X21) transition of the molecule. Analyses of the spectra have yielded a number of new or improved spectroscopic parameters of the molecules.

The b1Σ+(b0+) → X3Σ−(X10+, X21) and a1Δ(a2) → X3Σ−(X21) transitions of TeO

Chemiluminescence spectra of the TeO radical in the near-infrared spectral region have been measured with a high-resolution Fourier-transform spectrometer. The TeO molecules were generated and excited in a fast-flow system by reacting a microwave-discharged mixture of Tex vapor and Ar carrier gas with microwave-discharged oxygen. The b1Σ+(b0+)→X3Σ−(X10+, X21) transitions of TeO in the wavenumber range of 7800–11200cm−1 were reinvestigated at medium spectral resolution. A new sequence of bands observed near 4460cm−1 was assigned to the hitherto unknown a1Δ(a2)→X3Σ−(X21) transition of TeO. Vibrational analyses of the three band systems yielded the origins υe of the transitions and the vibrational constants of the X10+, X21, a2 and b0+ states of 130TeO.Also reported are some results of high-resolution measurements and rotational analyses of bands of the b0+→X10+ and b0+→X21 transitions of isotopically pure 130TeO carried out by one of us (K.D.S.) about 20years ago and hitherto published in a PhD thesis only.

CO2 laser drives extreme ultraviolet nano-lithography — second life of mature laser technology

AbstractIt was shown both theoretically and experimentally that nanosecond order laser pulses at 10.6 micron wavelength were superior for driving the Sn plasma extreme ultraviolet (EUV) source for nano-lithography for the reasons of higher conversion efficiency, lower production of debris and higher average power levels obtainable in CO2 media without serious problems of beam distortions and nonlinear effects occurring in competing solid-state lasers at high intensities. The renewed interest in such pulse format, wavelength, repetition rates in excess of 50 kHz and average power levels in excess of 18 kiloWatt has sparked new opportunities for a matured multi-kiloWatt CO2 laser technology. The power demand of EUV source could be only satisfied by a Master-Oscillator-Power-Amplifier system configuration, leading to a development of a new type of hybrid pulsed CO2 laser employing a whole spectrum of CO2 technology, such as fast flow systems and diffusion-cooled planar waveguide lasers, and relatively recent quantum cascade lasers. In this paper we review briefly the history of relevant pulsed CO2 laser technology and the requirements for multi-kiloWatt CO2 laser, intended for the laser-produced plasma EUV source, and present our recent advances, such as novel solid-state seeded master oscillator and efficient multi-pass amplifiers built on planar waveguide CO2 lasers.

ChemInform Abstract: Diisobutylaluminum Hydride Reductions Revitalized: A Fast, Robust, and Selective Continuous Flow System for Aldehyde Synthesis.

A continuous flow system for the multiparameter (flow rate, temperature, residence time, stoichiometry) optimization of the DIBALH reduction of esters to aldehydes is described. Incorporating an in-line quench (MeOH), these transformations are generally complete in fewer than 60 s. Mixing of the DIBALH and ester solutions was observed to be an exceptionally critical parameter for optimum results. This system thus provides general guidelines based on the structure of the ester for selective reduction of an ester without overreduction.

Analysis of Nascent Rotational Energy Distributions and Reaction Mechanisms of the Gas-Phase Radical-Radical Reaction O(3P)+(CH3)2CH→C3H6+OH

This paper reports on the gas-phase radical-radical dynamics of the reaction of ground-state atomic oxygen [O((3)P), from the photodissociation of NO(2)] with secondary isopropyl radicals [(CH(3))(2)CH, from the supersonic flash pyrolysis of isopropyl bromide]. The major reaction channel, O((3)P)+(CH(3))(2)CH→C(3)H(6) (propene)+OH, is examined by high-resolution laser-induced fluorescence spectroscopy in crossed-beam configuration. Population analysis shows bimodal nascent rotational distributions of OH (X(2)Π) products with low- and high-N'' components in a ratio of 1.25:1. No significant spin-orbit or Λ-doublet propensities are exhibited in the ground vibrational state. Ab initio computations at the CBS-QB3 theory level and comparison with prior theory show that the statistical method is not suitable for describing the main reaction channel at the molecular level. Two competing mechanisms are predicted to exist on the lowest doublet potential-energy surface: direct abstraction, giving the dominant low-N'' components, and formation of short-lived addition complexes that result in hot rotational distributions, giving the high-N'' components. The observed competing mechanisms contrast with previous bulk kinetic experiments conducted in a fast-flow system with photoionization mass spectrometry, which suggested a single abstraction pathway. In addition, comparison of the reactions of O((3)P) with primary and tertiary hydrocarbon radicals allows molecular-level discussion of the reactivity and mechanism of the title reaction.

Diisobutylaluminum Hydride Reductions Revitalized: A Fast, Robust, and Selective Continuous Flow System for Aldehyde Synthesis

A continuous flow system for the multiparameter (flow rate, temperature, residence time, stoichiometry) optimization of the DIBALH reduction of esters to aldehydes is described. Incorporating an in-line quench (MeOH), these transformations are generally complete in fewer than 60 s. Mixing of the DIBALH and ester solutions was observed to be an exceptionally critical parameter for optimum results. This system thus provides general guidelines based on the structure of the ester for selective reduction of an ester without overreduction.

ChemInform Abstract: FTIR Studies of Reactions Between the Nitrate Radical and Chlorinated Butenes.

The products formed in the reactions between the nitrate radical and 2-chloro-1-butene, 3-chloro-1-butene, 1-chloro-2-butene, and 2-chloro-2-butene were studied by FTIR spectroscopy. The experiments were performed in synthetic air in a glass/Teflon reactor and using N{sub 2}O{sub 5} as the NO{sub 3} source. The principal products formed with chlorobutenes, where the chlorine atom was substituted at a carbon participating in the double bond, were acid chlorides, aldehydes, and NO{sub 2}. The products formed from chlorobutenes with the chlorine atom substituted at a carbon next to the double bond were aldehydes, chlorinated carbonyl nitrate compounds, and NO{sub 2}. The reaction rate constant for the initial reaction step for 2-chloro-1-butene was determined to be 1.73 ({plus minus} 0.31) {times} 10{sup {minus}14} cm{sup 3} molecule{sup {minus}1} s{sup {minus}1} at 299 K by using a fast-flow system.