Third-order Recombination Research Articles

Script Independent Document Analysis for Forensics

Abstract: The main objective of this research is to utilize ink analysis for the identification of forgeries in handwritten documents, particularly checks. The completion of this study involves the application of motif feature extraction techniques, including Peano scan motif, Directional local motif, and third-order recombination between RGB planes. Following Method 1, the Peano scan motif is employed. To detect ink forgeries, 112 check images were examined, each written with fourteen different pens. A MATLAB function is applied to extract features for each of the mentioned approaches. The Weka application is utilized for both testing and training to validate the accuracy of the techniques. Typically, motif approaches like Peano scan motif, Directional local motif, and third-order recombination are used for identifying comparable items in databases, such as content-based picture retrieval systems. What sets this project apart is its innovative use of ink level forgery detection. The recombination approach, involving modified color planes and the previously mentioned Peano scan motif method, introduces a novel aspect to the study.

Tracking carrier and exciton dynamics in mixed-cation lead mixed-halide perovskite thin films

Mixed-cation lead mixed-halide perovskites simultaneously possess structural stability and high power conversion efficiency. A thorough study of both carrier and exciton dynamics is needed to understand the photophysical properties that underpin its superior photovoltaic performance. By utilizing a broadband transient absorption spectroscopy, we observe the carrier and exciton dynamics in a FA0.85Cs0.15Pb(I0.97Br0.03)3 (FCPIB) perovskite by simultaneously resolving the carrier and exciton contribution to the transient change of the absorption spectra, from which the carrier density and exciton oscillator strength can be determined. Our data reveal a quick and significant conversion of the photogenerated carriers to excitons, on top of the usual carrier recombination process. Moreover, the decay of carrier density shows a change of kinetics from a second-order recombination at high pump fluence to a third-order recombination at low pump fluence. Our analysis utilizes band anharmonicity, presents an independent determination of electronic temperature and quasi-Fermi energy, and reveals an interesting interplay among the processes of carrier cooling, exciton formation/decay and carrier recombination, all as a function of time after photoexcitation. Our work demonstrates the use of pump fluence as a knob to tune the relative populations of carriers and excitons in halide perovskite materials.

Ultrafast Carrier Recombination and Transient Lattice Temperature Changes in 25 nm Thin Hydrogenated Amorphous Silicon Films

Hydrogenated amorphous silicon (a-Si:H) represents an important material for optoelectronic and photovoltaic applications. Fundamental knowledge regarding its charge carrier dynamics and thermalization behavior after photoexcitation is therefore required. Here, we provide a detailed broadband UV–vis–NIR transient absorption study of 25 nm thin a-Si:H films on glass upon pumping at 390, 400, or 650 nm, covering the wavelength range 300–1600 nm. Photoexcited carriers relax in the extended states within a few hundred femtoseconds and recombine very quickly. In contrast to a previously suggested bimolecular recombination mechanism for carrier densities larger than 5 × 1018 cm–3, we unambiguously identify Auger-type third-order recombination with the rate constant k3 = (2.3 ± 0.6) × 10–29 cm6 s–1, which is extracted from the absorption decay in the NIR region. The released recombination energy leads to a fast lattice heating which is indicated by a fast rise of absorption in the UV–vis region. This spectral fe...

Mismatch of non-geminate recombination in polymer TQ1/fullerene blends employing different techniques

The non-geminate recombination was investigated in TQ1:PC61BM:PC71BM (poly[[2,3-bis(3-octyloxyphenyl)-5,8-quinoxalinediyl]-2,5-thiophenediyl]:[6,6]-Phenyl-C61-butyric-acid-methyl-ester:[6,6]-Phenyl-C71-butyric-acid-methyl-ester) bulk heterojunctions employing the extraction of the photogenerated charge carriers by linearly increasing voltage (photo-CELIV) and integral Time-of-Flight (ToF) techniques. The shapes of photo-CELIV and ToF transients point out purely non-reduced Langevin recombination while the decay of the photogenerated charge carrier density measured with photo-CELIV technique indicates reduced third-order recombination. A clear discrepancy could be explained by spatially separated holes and electrons during the delay time while employing photo-CELIV method.

Recombination coefficients of GaN-based laser diodes

We measure the charge carrier recombination coefficients of InGaN quantum wells by analyzing the dynamical properties of (Al,In)GaN laser diodes emitting in the violet spectral range. Relaxation oscillations and turn-on delays are fitted to a rate equation model including a charge carrier density dependent recombination rate. Using optical gain spectroscopy we can directly determine the injection efficiency of the devices and thereby separate the effect of charge carrier leakage from that of carrier recombination. We find a third-order recombination coefficient of (4.5±0.9)×10-31cm6s-1 which is in agreement with theoretical predictions for phonon- and alloy-disorder-assisted Auger scattering.

Temperature and Pressure Dependent Rate Coefficients for the Reaction of Hg with Br and the Reaction of Br with Br: A Pulsed Laser Photolysis-Pulsed Laser Induced Fluorescence Study

A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and bromine atoms, Hg + Br + M --> HgBr + M (1) and the self-reaction of bromine atoms, Br + Br + M --> Br2 + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in nitrogen buffer gas and as a function of pressure (200-600 Torr) in helium buffer gas at room temperature. For reaction 1, kinetic measurements were performed under conditions in which bromine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both mercury and bromine. A temperature dependent expression of (1.46 +/- 0.34) x 10(-32) x (T/298)(-(1.86+/-1.49)) cm6 molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is a factor of 9 smaller than previously determined in a recently published relative rate study. For reaction 2 we obtain a temperature dependent expression of (4.31 +/- 0.21) x 10(-33) x (T/298)(-(2.77+/-0.30)) cm6 molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute bromine atom concentrations and other unidentified systematic errors we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature and buffer gas dependencies are consistent with the expected behavior for three-body recombination.

Temperature and Pressure Dependent Rate Coefficients for the Reaction of Hg with Cl and the Reaction of Cl with Cl: A Pulsed Laser Photolysis−Pulsed Laser Induced Fluorescence Study

A pulsed laser photolysis-pulsed laser induced fluorescence technique has been employed to study the recombination of mercury and chlorine atoms, Hg + Cl + M --> HgCl + M (1), and the self-reaction of chlorine atoms, Cl + Cl + M --> Cl(2) + M (2). Rate coefficients were determined as a function of pressure (200-600 Torr) and temperature (243-293 K) in N(2) buffer gas and as a function of pressure (200-600 Torr) in He buffer gas at room temperature. For reaction (1) kinetic measurements were obtained under conditions in which either mercury or chlorine atoms were the reactant in excess concentration while simultaneously monitoring the concentration of both reactants. An Arrhenius expression of (2.2 +/- 0.5) x 10(-32) exp{(680 +/- 400)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) was determined for the third-order recombination rate coefficient in nitrogen buffer gas. The effective second-order rate coefficient for reaction 1 under atmospheric conditions is much smaller than prior determinations using relative rate techniques. For reaction (2) we obtain an Arrhenius expression of (8.4 +/- 2.3) x 10(-33) exp{(850 +/- 470)((1)/(T) - (1)/(298))} cm(6) molecule(-2) s(-1) for the third-order recombination rate coefficient in nitrogen buffer gas. The rate coefficients are reported with a 2sigma error of precision only; however, due to the uncertainty in the determination of absolute chlorine atom concentrations we conservatively estimate an uncertainty of +/-50% in the rate coefficients. For both reactions the observed pressure, temperature, and buffer gas dependencies are consistent with the expected behavior for three-body recombination.

Kinetic Investigation of the Reaction Sr(1S) + O2 + He in the Temperature Range from 303 to 968 K

A kinetic study of the third-order recombination reaction Sr(1S) + O2 + He SrO2 + He has been carried out in a fast-flow reactor in the temperature and pressure range of respectively 303−968 K and 6−12 Torr. Strontium atoms were generated by thermal evaporation of strontium metal pellets and then monitored by atomic absorption spectroscopy (AAS). The Arrhenius plot shows a departure from linearity above 500 K. The modified Arrhenius expression taking into account a temperature dependence of the preexponential factor for the entire temperature range results in the expression k1Sr(He) = [(1.9 ± 0.3) × 10-23]T-1.7 exp[(−12.1 ± 0.8 kJ mol-1)/RT] cm6 molecule-2 s-1. The best representation of the temperature dependence is given by the polynomial fit log k1Sr(He) = −60.83 + 22.44(log T) − 3.89(log T)2. A lower limit to the bond energy of the SrO2(3A2) reaction product is estimated by means of the method based on the expression of the equilibrium constant and the theory of statistical mechanics. A value of D0 > 244 kJ mol-1 was obtained, which is in the range of the values derived from ab initio calculations.

Kinetics of the reactions of CH3O and CD3O with NO

The kinetics of the reactions of CH3O and CD3O with NO have been studied using a discharge flow reactor. CH3O and CD3O were detected using laser-excited fluorescence (LEF) near 300 nm. Total rate coefficients for the reaction of CH3O with NO were measured as a function of temperature (220–473 K) and pressure (0.75–5.0 Torr) of He or Ar. Total rate coefficients for the CD3O + NO reaction were measured at ca. 294 K over the pressure range 0.75–5.0 Torr He. Using molecular-beam mass spectrometry, the CH3ONO yield of the CH3O + NO reaction was measured at 297 K (0.5 and 1.0 Torr) and 223 K (1.0 Torr), showing that disproportionation to H2CO + HNO is the major channel at low pressures. These results were combined to obtain the following expressions for the disproportionation and low-pressure recombination rate coefficients.For the CH3O + NO reaction, kDISP=(1.3 ± 0.4)× 10–12 exp[(250 ± 100)/T] cm3 s–1, kIII0=(1.8 ± 1.3)× 10–29(T/300)–(3.2 ± 0.5) cm6 s–1For the CD3O + NO reaction at 294 ± 2 K kDISP=(3.0 ± 0.4)× 10–12 cm3 s–1 and kIII0=(2.5 ± 0.4)× 10–29 cm6 s–1 While the uncertainty associated with the measured rate coefficients is ca.± 15%, the product channel-specific rate coefficients obtained from these expressions are less certain, ca.± 50%.Using MBMS, the CH3NO2 yield of the CH3+ NO2 reaction was measured at 297 K (0.5 and 1.0 Torr) and 223 K (1.0 Torr). Combined with the previously reported rate coefficient, these results indicate a low-pressure, third-order recombination rate coefficient of (6 ± 2)× 10–29 cm6 s–1 in He at 297 K.

Temperature dependence of the absolute third-order rate constant for the reaction between K + O 2 + N 2 over the range 680–1010K studied by time-resolved atomic resonance absorption spectroscopy

We present a direct kinetic study of the third-order recombination reaction K+O 2+N 2→KO 2+N 2 across the temperature range 680–1010K. K(4 2S 1 2 ) was generated by pulsed irradiation and monitored by time-resolved atomic resonance absorption spectroscopy in the “single shot mode” in the presence of O 2 and N 2 using the Rydberg transition at λ = 404 nm ( K(5 2P J) ← K(4 2S 1 2 ) ). While the resulting data for k 4 can be empirically expressed within this temperature range by the form k 4(680–1010 K) = (6.63 ± 0.66 × 10 −23)( T K ) −2.6±0.28 cm 6 molecule −2 s −1, a full extrapolation based on the unimolecular rate theory of Tröe was carried out in order to extend the data to flame temperatures (2000K), given the importance of potassium additives in flame inhibition. The full extrapolation across the range 200–2000K can be expressed to within 10% by (k 4/cm 6 molecule −2S −1)=−0.2558 [ln( T K )] 2+1.361 ln( T K )−66.14 These results are compared with data derived from measurements on a fast flow reactor which show a much smaller temperature dependence and indicate an extrapolated value for k 4 at flame temperatures significantly higher than derived from the present investigations.

The temperature dependence of the yellow glow from active nitrogen

A discharge flow/shock tube has been used to investigate the change in emission, in the temperature range 300–1200 K, for the ν= 6, 10, 11 and 12 levels of N2(B3Πg) in discharged nitrogen. For each level the emission decreased with temperature and empirical equations are given to describe the behaviour. The results are interpreted qualitatively in terms of the Thrush mechanism modified to include the N2(W3Δu) state. The general decrease is attributed to the fall in the third-order recombination rate constant; the detailed differences between levels are correlated with the varying energy spacings between the vibrational levels of the N2(B3Πg) and N2(W3Δu) states. A second peak in the emission traces, attributed to the early arrival of the contact surface, is observed at much longer times than those during which the main measurements are made. It is observable only because of the inverse temperature dependence of the emission and so our experimental methods offer a unique way of studying contact surface and boundary layer processes.

Band-to-band Auger Recombination in Silicon and Germanium

High concentrations of electrons and holes in silicon and germanium have been achieved by optical injection by a giant pulse ruby laser. The kinetics and spectral distribution of the recombination radiation during and after the injection pulse have been analyzed by a theoretical model which takes into account the heating of the sample by the laser pulse as well as the decrease of the band gap which is due to the high carrier concentration. The decay of the recombination radiation signal shows that a third-order recombination process (band-to-band impact or Auger recombination) is predominant at high concentrations. The value of the Auger recombination coefficient γ3 ≃ 10-31 - 4 × 10-30 cm6/s is obtained for silicon in the temperature interval 300 K-800 K.

Kinetics of collisional ionization of alkali metal atoms and recombination of electrons with alkali metal ions in flames

The rate constant k2 has been measured in flames of H2 + O2 + N2 for the ionization of alkali metal atoms M in collisions with flame species X in M+X→M++e−+X. Results are compared with every previously reported measurement of k2 in similar flames for each alkali metal. It is concluded that k2=(9.9±2.7)×10−9T1/2exp⁡(−V/RT), ml molecule −1 sec−1, where V is the ionization potential of the alkali metal atom and T the temperature. k2 does not depend on flame composition and is the same for each alkali to a good approximation.The third-order recombination rate constant k−2 for the reverse of (II) can be written as k−2=(4.1±1.1)×10−24T−1, ml2 molecule−2 sec−1. There is no significant dependence of k−2 on flame composition or on which alkali metal is considered. These facts enable the rates of the forward and reverse processes in (II) to be estimated in flames generally.

Third-order recombination reactions of NF2 radicals

The kinetics of elementary reactions of ground state NF2 radicals, produced by thermal dissociation of N2F4 in a low pressure flow system, were investigated at 293 K. The third order reaction (1) was characterized: NF2+ NF2+ M [graphic omitted] N2F4+ M;(1) values for k1,M(10–32 cm6 molecule–2 s–1) at 293 K were: k1,Ar=(1.26± 0.15); k1,He=(0.76± 0.15); k1,SF6=(2.93± 0.30); k1, 02=(0.98± 0.18).Reactions of Cl and Br 2Pfrac32; atoms with NF2 radicals in Ar carrier gas were also third order: NF2+ Cl + Ar [graphic omitted] NF2Cl + Ar; NF2+ Br + Ar [graphic omitted] NF2Br + Ar. At 293 K, k2,Ar=(2.7 ± 0.4)×10–31, k3,Ar=(1.0 ± 0.2)× 10–31 cm6 molecule –2 s–1. Second order rate constants at 293 K for the reactions NF2Cl + Cl, NF2Br + Br, were > 2 × 10–14 cm3 molecule–1 s–1. The stabilities of NF2Cl and NF2Br are discussed.

Bimolecular Reaction of N2O with CO and the Recombination of O and CO as Studied in a Single-Pulse Shock Tube

The reaction between N2O and CO was studied in a single-plus shock tube over the temperature range 1320°–2280°K, in mixtures of the reactants highly diluted with Ar. In the range of temperatures 1317°–1908°K the rate constant for the bimolecular reaction, N2O+CO→ lim 1N2+CO2, was found to be k1 = 1.1 × 1011exp(− 23 000 / RT) cm3mole−1·sec−1. From the rates of formation of CO2 above 1642°K, a constant for the nonradiative third-order recombination of O and CO was obtained (for the temperature range 1500°–3000°K), O+CO+Ar5→ lim 5CO2+Ar, k5 = 2.8 × 1012exp(+ 23 800 / RT) cm6mole−2·sec−1. The large negative activation energy so deduced is shown to be in full agreement with the low value for the activation energy previously observed for CO2 decomposition. An energy diagram was constructed on the basis of a recent CO flame study and results on the limiting high-pressure CO2 decomposition. The mechanisms for the radiative and the three-body recombination, and the dissociation of CO2, are discussed in terms of this energy diagram.

The kinetics of the thermal decomposition of trifluoroacetaldehyde

The thermal decomposition of trifluoroacetaldehyde has been studied at temperatures between 471� and 519�, and at pressures up to 180 mm. The main products of reaction are trifluoromethane and carbon monoxide in equal amounts; small amounts of hexafluoroethane and hydrogen are also formed. The experimental rate equation governing the observed kinetics is of the form Rate = k?[CF3CHO]3/2, where k? = 1012.2exp(-49000/RT) l.� mole-1 sec-1 A small surface effect is apparent, an increase in surface area causing an increase in rate. Inert gases, namely carbon monoxide and dioxide, increase the rate of decomposition, the experimental rate equation assuming the form Rate = (k'[CF3CHO]3 + k"[CF3CHO]2.2[M])� A mechanism is proposed which predict,^ the experimental form of the rate equation and involves initiation through a second-order energy transfer process followed by a radical chain mechanism, the length of which is 1200 with P(CF3CHO) = 200 mm. Termination is considered to be through the third-order recombination of trifluoromethyl radicals.

Mechanism of third-order recombination reactions

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