Spectroscopic flame temperature measurements and their physical significance—IV Importance of the transition probability factor

A comparison of flame temperatures measured by the well-known spectroscopic “slope” method for Fe thermometric species residing in an isothermal, optically-thin environment shows that a range of 150°K is obtained when several different sets of recommended transition probabilities are used for the determinations. A similar lack of self-consistency is also shown by the temperatures obtained from two groups of Fe lines when the same set of transition probabilities is employed. These uncertainties have not been generally recognized.     

Inductively coupled plasma-optical emission spectroscopy : Excitation temperatures experienced by analyte species

Spatially resolved, radical excitation temperature distributions experienced by analyte species injected into the axial channel of a toroidally shaped, inductively coupled argon plasma are presented. Typical axial temperatures experienced by the thermometric species (FeI) ranged from 6500 K to 5500 K in the analytical zone of 15–25 mm above the load coil. A comparison of temperatures calculated with different sets of transition probabilities is also given.     

Spectroscopic flame temperature measurements and their physical significance—II: Results from flame model calculations

Apparent temperatures have been calculated for several theoretical flame models representing typical laboratory flames. These apparent temperatures correspond to those temperature values which would have been measured by the line reversal, emission-absorption, two-line and slope methods if the theoretical models correspond to real flames. It is shown that differences as large as 800 K may arise between the measured values and the average or weighted average temperatures. Moreover, temperatures measured by the same technique and thermometric species but with different spectral lines may differ by as much as 200 K even if no other errors are involved, such as uncertainties in the transition probabilities. Physical interpretations that go beyond these uncertainties flatter the actual experimental situations and are not justified.     

微波等离子体增强辉光放电光源激发温度的研究

研究了一种改进型的微波等离子体增强辉光放电光源在光谱分析中的应用，对其重要的参数指标－激发温度进行了较为较细的考察。结果表明引入微波等离子体后辉光放电的激发温度明显高于单纯辉光放电时的激发温度。     

Transition probabilities for some infrared O I spectral lines—Application for determining excitation temperatures in low temperature plasmas

Intensities of selected spectral transitions of neutral oxygen emitted from a wall-stabilized arc have been measured. Applying reliable transition probability data taken from literature, Boltzmann plots have been constructed and the temperatures of the plasma have been obtained. At arc plasma conditions ensuring partial local thermal equilibrium, transition probabilities for 4 O I spectral lines from the near infrared spectral range have been obtained. These new results, together with data for two other studied O I spectral lines taken from the National Institute of Standards and Technology data base, are proposed as a suitable set of transition probabilities applicable for diagnostics of low temperature plasmas.     

Spectroscopic flame temperature measurements and their physical significance—V. Experimental determination of relative transition probabilities for 43 Fe I lines in the 3450–3950 Å wavelength region

Relative transition probabilities, as measured by the atomic emission spectroscopic technique, have been redetermined for 43 lines of Fe I under experimental conditions that in principle should yield accurate values. The Fe free-atoms are formed in a high temperature environment that has been shown to be isothermal and optically thin under the experimental conditions employed. The temperature of the iron atoms was measured by the reversal method, and the emission measurements were made so that the values obtained were strictly proportional to the line radiances. The high degree of correlation of the values reported with those obtained by the hook method is indicative of the overall reliability of these sets of data.     

Spatial distribution of the temperature and the number densities of electrons and atomic and ionic species in an inductively coupled RF argon plasma

A survey of the literature shows that the values found for the excitation parameters (temperature and electron number density) in an inductively coupled radio-frequency argon plasma at atmospheric pressure (ICP) depend on the plasma configuration and the measuring procedure. The present study proposes a novel method for measuring excitation temperatures that does not require a knowledge of transition probabilities. The experimental work concerns measurements of the spatial distributions of the temperature, the number densities of the electrons and various atomic and ionic species in a low-power (～0.5 kW) ICP for analytical purposes operated at either of two extreme carrier gas flow rates. Observations were made at three different heights above the induction coil. At high flow rate (～51/min) the familiar hollow configuration of the plasma is demonstrated by off-axis maxima for the temperature and the number densities of electrons and atomic species at all observation heights. At low flow rate (～1 l./min), the radial atom number density distributions are parabolically shaped and constricted to a smaller channel at all observation heights. The authors conclude from the results that both the plasma configurations are not in a state of complete local thermal equilibrium at observation heights used for analytical work (i.e., above the coil).     

Measurements of transition probabilities for two N I infrared transitions and their application for diagnostics of low temperature plasmas

Spectra emitted from a wall-stabilized arc, running in a gas mixture of helium, argon, nitrogen, oxygen and traces of hydrogen have been studied. Intensities of selected spectral transitions of neutral nitrogen and oxygen have been measured. Applying the Boltzmann plot method and using a reliable set of O I transition probabilities of spectral lines, originating from levels considerably spread in excitation energies, the temperatures of arc plasmas have been determined. Line intensities of two N I infrared transitions, originating from doubly excited terms 3p′ ²F^o and 3p′ ²G have been measured. In order to obtain the corresponding transition probabilities (A_ki) for these lines, intensities of other N I infrared lines, with well known transition probabilities (taken from recently published data by Wiese and Fuhr [W.L. Wiese and J.R. Fuhr, Improved critical compilations of selected atomic transition probabilities for neutral and singly ionized carbon and nitrogen, J. Phys. Chem. Ref. Data 36 (2007) 1287–1345] from National Institute of Standards and Technology — NIST) have been measured. For evaluation of the transition probabilities the temperatures obtained from the above mentioned O I Boltzmann plots have been used. The results agree satisfactorily with older data found in literature. The new A_ki values for transitions involving the doubly excited levels, together with A_ki values taken from the above mentioned NIST source (used for determination of the new A_ki values), are proposed as a convenient set for determining temperatures of plasmas containing nitrogen atoms.     

Glass transition temperature of glucose, sucrose, and trehalose: an experimental and in silico study

Isothermal-isobaric molecular dynamics simulations are used to calculate the specific volume of models of different amorphous carbohydrates (glucose, sucrose, and trehalose) as a function of temperature. Plots of specific volume vs temperature exhibit a characteristic change in slope when the amorphous systems change from the glassy to the rubbery state. The intersection of the regression lines of data below (glassy state) and above (rubbery state) the change in slope provides the glass transition temperature (T(g)). These predicted glass transition temperatures are compared to experimental T(g) values as obtained from differential scanning calorimetry measurements. As expected, the predicted values are systematically higher than the experimental ones (about 12-34 K) as the cooling rates of the modeling methods are about a factor of 10(12) faster. Nevertheless, the calculated trend of T(g) values agrees exactly with the experimental trend: T(g)(glucose) < T(g)(sucrose) < T(g)(trehalose). Furthermore, the relative differences between the glass transition temperatures were also computed precisely, implying that atomistic molecular dynamics simulations can reproduce trends of T(g) values in amorphous carbohydrates with high quality.     

Atomic transition probabilities for selected Yb II lines emitted from a ferroelectric plasma source

The relative intensities of several hundred emission lines of Yb II between 200 nm and 900 nm were obtained with the use of ferroelectric plasma source. These relative intensities obtained for lines from 21 energy levels have been used to determine the line branching fractions, which have then been combined with accurate experimental radiative lifetime measurements to give absolute transition probabilities for 111 Yb II lines. The obtained values were compared with theoretical and experimental data taken from available literature.     

A spectroscopic study of laser-induced tin–lead plasma: Transition probabilities for spectral lines of Sn I

In this paper, we present transition probabilities for 97 spectral lines of Sn I, corresponding to transitions n(n = 6,7,8)s → 5p², n(n = 5,6,7)d → 5p², 5p³ → 5p², n(n = 7)p → 6s, determined by measuring the intensities of the emission lines of a Laser-induced breakdown (emission) spectrometry (LIBS). The optical emission spectroscopy from a laser-induced plasma generated by a 10 640 Å radiation, with an irradiance of 1.4 × 10¹⁰ Wcm^− 2 on an Sn–Pb alloy (an Sn content of approximately 20%), in vacuum, was recorded at 0.8 µs, and analysed between 1900 and 7000 Å. The population-level distribution and corresponding temperature were obtained using Boltzmann plots. The electron density of the plasma was determined using well-known Stark broadening parameters of spectral lines. The plasma under study had an electron temperature of 13,200 K and an electron number density of 2 × 10¹⁶ cm^− 3. The experimental relative transition probabilities were put on an absolute scale using the branching ratio method to calculate Sn I multiplet transition probabilities from available radiative lifetime data of their upper states and plotting the Sn I emission spectrum lines on a Boltzmann plot assuming local thermodynamic equilibrium (LTE) to be valid and following Boltzmann's law. The LTE conditions and plasma homogeneity have been checked. Special attention was paid to the possible self-absorption of the different transitions. The experimental results obtained have been compared with the experimental values given by other authors.     

Atmospheric pressure,radio frequency,parallel plate capacitively coupled plasma—excitation temperatures and analytical figures of merit

Electronic excitation (T_exc) and rotational (T_rot) temperatures were determined for a parallel plate capacitively coupled rf plasma operating at atmospheric pressure. T_exc was calculated from the slope of the Boltzmann plot using Fe and He as the thermometric species and Pb excitation temperature was calculated using the two line method. Over a power range from 100 W to 250 W, excitation temperatures are 3255–3900 K for He, 3540–4500 K for Pb, and 4300–4890 K for Fe. The rotational temperature was measured using both OH and N₂⁺ molecular spectra and the values are in the range of 828–911 K and 845–956 K respectively over a power range of 75–275 W. Signal-to-noise ratios, signal-to-background ratios, and absolute detection limit for lead (0.33 ng) and silver (24 pg) are also reported.     

A novel method for estimation of transition temperature for polymorphic pairs in pharmaceuticals using heat of solution and solubility data

A novel method for thermodynamic stability studies of polymorphic drug substances has been developed. In order to estimate the transition temperature for an enantiotropic polymorphic pair, a formula for calculating the temperature at which the solubilities of each polymorph become equal has been derived with heat of solution and solubility as the variables. This formula is based on the assumption that van't Hoff plots (logarithmic solubility versus reciprocal of absolute temperature plots) of each polymorph show a straight line (heat of solution is independent of temperature) whose slope can be expressed as a function of heat of solution. The transition temperatures for seratrodast, acetazolamide and carbamazepine polymorphic pairs calculated by the formula were in good agreement with the results of previous studies. Furthermore, the calculated transition temperature for the indomethacin polymorphic pair was above the melting point, an unrealistic temperature range, suggesting that these polymorphs are monotropically related. Since this formula requires solubility data at only one arbitrary temperature other than heat of solution data for both polymorphs in a polymorphic pair, the proposed method is much faster than the conventional method requiring solubility data at five or more different temperatures for the preparation of van't Hoff plots.     

Comparison of zinc and cadmium plasma parameters produced by laser-ablation

We report the measurement of the zinc and cadmium plasma parameters produced by the fundamental, second, and third harmonics of the neodymium-doped yttrium aluminium garnet laser. The excitation temperature has been determined from the Boltzmann plot method, whereas the electron number density is estimated from the Stark broadened profile of several spectral lines. The temporal evolution of the plasma has also been investigated. Besides, we present experimental relative transition probabilities of the Zn (4s5s ³S₁ → 4s4p ³P_0,1,2) and Cd (5s6s ³S₁ → 5s5p ³P_0,1,2) triplets and compare our data with that listed in the National Institute of Standards and Technology database. The experiments have been performed in air but also in He, Ne and Ar atmosphere to study the effects of ambient gas environment on the emission intensity of the atomic and ionic lines and on the plasma parameters.     

Temperaturmessungen am Argon-Niederstrombogen zur Bestimmung der Übergangswahrscheinlichkeiten von Si I-, Se I- und S I-Linien im nahen Vakuum-UV

The temperatures of scon-cooled argon-d.c.-arc under variousexperimental conditions have been measured. It is shown that the Ornstein-method can be applied in the vacuum-ultraviolet region because the optimum temperatures of the spectral lines in this region are very high. The temperature of the arc has been determined in respect to the electric current and the electrode distance. The temperature of the arc rises with increasing current, whereas by varying the distance of the electrodes a temperature maximum is observed which can be explained by the amount of power absorbed by the electrodes. The relative transition probabilities of several lines of Si I, Se I and S I in the vacuum-u.v. have been measured. Some of the values which had already been determined theoretically and experimentally by other authors agree very well with our results.     

Model for measuring excitation temperatures on a relative basis without transition probabilities

A variation of the conventional slope or two-line method is proposed for determining excitation temperature (T_exc) by atomic emission. T_exc is measured relative to some known reference value, which can be derived either from the emission source itself or from some reference line source of known temperature. Measurement of T_exc with a relative error of 1–10% should be possible for reasonable experimental uncertainties in T_ref and the measured line intensities. The proposed method is useful for some interesting and important experiments with emission lines for which the transition probabilities are either unknown or of questionable accuracy. Such experiments include measuring the dependence of T_exc on observation position or operating parameters, determining whether or not different emitting species have the same T_exc, and identifying possible deviations from a Boltzmann distribution of excited state populations within a particular emitting species.     

低功率微波等离子体炬（MPT）光源基本性质的初步研究

对低功率微波等离子体炬(MPT)光源基本性质进行了初步研究,采用“双线法”测定了有、无样品引入时光源中激发温度随观测高度的变化;测定了Zn、Cd、Mg的原子线和离子线发射强度随观测高度的变化;还研究了一些实验参数对等离子体激发温度的影响。     

Seven-dimensional quantum dynamics study of the H+NH3-->H2+NH2 reaction

Initial state-selected time-dependent wave packet dynamics calculations have been performed for the H+NH3-->H2+NH2 reaction using a seven-dimensional model and an analytical potential energy surface based on the one developed by Corchado and Espinosa-Garcia [J. Chem. Phys. 106, 4013 (1997)]. The model assumes that the two spectator NH bonds are fixed at their equilibrium values. The total reaction probabilities are calculated for the initial ground and seven excited states of NH3 with total angular momentum J=0. The converged cross sections for the reaction are also reported for these initial states. Thermal rate constants are calculated for the temperature range 200-2000 K and compared with transition state theory results and the available experimental data. The study shows that (a) the total reaction probabilities are overall very small, (b) the symmetric and asymmetric NH stretch excitations enhance the reaction significantly and almost all of the excited energy deposited was used to reduce the reaction threshold, (c) the excitation of the umbrella and bending motion have a smaller contribution to the enhancement of reactivity, (d) the main contribution to the thermal rate constants is thought to come from the ground state at low temperatures and from the stretch excited states at high temperatures, and (e) the calculated thermal rate constants are three to ten times smaller than the experimental data and transition state theory results.     

A rotational thermalization model for the calculation of collisionally narrowed isotropic raman scattering spectra - application to the SRS N2 Q-branch

A model for the calculation of collisionally narrowed isotropic. Raman scattering spectra is proposed. In this model, the rotational transition probabilities are calculated within the strong collision approximation, allowing the rotational energy transfer rates to be expressed in terms of the sole individual Q(J) line broadening coefficients. These transfer rates satisfy both detailed balance principle and unitarity of the scattering matrix in contrast with most of the previous approaches. Under further approximation concerning the rotational distribution of the collisional frequency, simpler expressions for transfer rates are deduced, which do not satisfy necessarily both unitarily and detailed balance. A simple analytical expression for the Q-branch profile is then obtained. An experimental study of the isotropic Q-branch for N₂ as a function of pressure has been conducted at room temperature by stimulated Raman spectroscopy (SRS). The Q-branch profiles calculated from the present model show a good agreement with SRS experiments, in particular when the lines overlap and when collisional narrowing takes place. This agreement is quite similar to that obtained by using a polynomial inverse energy gap law to describe the rotational energy transfer rates, and the results of these two models are closer for higher temperatures. The simple analytical expression mentioned above for the Q-branch profile, which is inaccurate at room temperature, becomes reliable at high temperature.