First measurement of electron-cyclotron emission spectra from PLT

The frequency spectrum of electron-cyclotron radiation from the PLT-device has been measured by observing in a vertical direction. The line profiles of 2ω_ce and 3ω_ce are broad and show a central intensity dip. An interpretation is given in terms of reflections on the vacuum vessel and self-absorption.     

An experimental investigation of partial LTE for lower excited levels of Ar(I) in a wall-confined,argon arc plasma

This paper contains experimental results on partial LTE in the lower excited levels of Ar(I). The experiments were performed in a well-confined argon arc source. The population densities were obtained from self-absorption measurements of the lines. Plasma parameters were determined spectroscopically; measurements included the electron density (from the H_β line width) and the electron temperature (from the Boltzmann plot for higher excited levels of Ar(I)). The results show that the levels 1s₅ to 1s₅ are in Saha-Boltzmann equilibrium for electron densities above 3 × 10¹⁶ cm^-3.     

Auger spectroscopy of polyethylene and poly (ethylene oxide)

The X-ray excited Auger spectra of polyethylene and poly(ethylene oxide) have been corrected for Auger electron energy losses due to interactions with the solid and compared to the corresponding spectra of gas phase molecular analogs. The corrected polyethylene spectrum is an extrapolation of trends observed in the spectra of gas phase alkanes from CH₄ through C₆H₁₄. The O(KVV) spectrum of poly(ethylene oxide) is similar to that of methyl ether, consistent with similar nearest neighbor environments for the oxygen atoms in the two materials. In contrast, the C(KVV) spectrum of poly(ethylene oxide), a material which contains C-C bonds, is better approximated by the spectrum of ethane (H₃C-CH₃). A comparison of the polyethylene Auger spectrum with the spectra of the normal alkanes and with a self-fold of its X-ray excited valence band photoemission (single hole) spectrum indicates the presence of correlated two-hole final states in the case of polyethylene.     

Measurement and analysis of the far infrared absorption spectrum of the gaseous mixture H2-CH4

The collision-induced absorption of H₂-CH₄ mixtures was measured from ∼20 to 900 cm^-1 at 195 and 297 K. By subtracting the absorption due to H₂-H₂ and CH₄-CH₄ collisions from that of the mixture, the absorption due to H₂-CH₄ collisions was obtained. This spectrum was analyzed using the BC model line shape to provide a way of estimating the far-i.r. spectrum of H₂-CH₄ for various concentrations of H₂ and CH₄. Theoretical spectral moments were computed with different potential functions and compared with experimental values.     

Indirect and direct optical transitions in the self-absorption spectra of SbI3 single crystals

The long-wave self-absorption edge of SbI₃ single crystals in the 293–95 ° K temperature range and their reflection spectrum inside the self-absorption band at room temperature were investigated. The absorption associated with indirect and direct interband transitions was isolated. The principal parameters characterizing indirect and direct optical transitions were determined.     

Line positions and intensities for the ν1 + ν2 and ν2 + ν3 bands of H2O

The intensities of about 90 lines of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O have been measured using a Fourier transform spectrum of natural water vapor. The constants involved in the rotational expansion of the transformed transition moment operators corresponding to these bands have been determined through a fit of these line intensities. The constants obtained are used to compute the whole spectrum of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O providing reliable line positions and intensities. For lines involving perturbed levels a comparison is given with the results obtained for H₂¹⁶O and it is shown that the results for one isotopic species cannot be transferred directly to another one.     

有自吸收现象时谱线强度与物质浓度的关系

谱线强度(I)与物质浓度(C)之间的定量关系是定量光谱分析的物理基础。由于实际光源中的谱线或多或少地都有自吸收现象,所以在实际情形下,I与C的关系是较为复杂的。本文中应用迁移取样法进行铸铁中的硅的光谱分析,选择了适当的条件,使Si 2516多重谱线系中的Si 2519线在光源中不发生自吸收,因而可以用它的强度代表光源中的物质浓度,同时测定了多重谱线系中发生自吸收最严重的Si 2516线的定标曲线斜度b与物质浓度C的关系(b=klogC+β+1),从而得出I与C的关系式如下:logI=k/2(logC)²+(β+1)logC+α,这里β与α是试验条件下的两个常数;k是b与logI₂₅₁₉的关系直线的斜度。在理想的情形,当谱线没有自吸收时,b=1,k=0,所以logI与logC之间便有直线的关系;当谱线有自吸收时,谱线的强度与物质的浓度有抛物线的关系。这个关系式所描述的与在较大浓度范围内一般实验中所观察的一致。     

Line positions and intensities for the ν1 + ν2 and ν2 + ν3 bands of H218O

The intensities of about 90 lines of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O have been measured using a Fourier transform spectrum of natural water vapor. The constants involved in the rotational expansion of the transformed transition moment operators corresponding to these bands have been determined through a fit of these line intensities. The constants obtained are used to compute the whole spectrum of the ν₁ + ν₂ and ν₂ + ν₃ bands of H₂¹⁸O providing reliable line positions and intensities. For lines involving perturbed levels a comparison is given with the results obtained for H₂¹⁶O and it is shown that the results for one isotopic species cannot be transferred directly to another one.     

Dependence of the spectral width of the self-absorbed Sr 4607.33Åresonance line on Sr atomic density in a flame

Using a pressure-scanned Fabry-Pérot interferometer, we measured spectral profiles of the self-absorbed Sr resonance line at 4607.33Åemitted in a pre-mixed, laminar, shielded air-C₂H₂ flame at 1 atm for various Sr-solution concentrations. The dependence of the full width at one-half maximum (FWHM) on Sr atomic density in the flame was found to agree with a calculation based on the Voigt expression and Beer's law. It appears that one can derive the FWHM under optically thin conditions (i.e. at vanishing Sr atomic density) by linear extrapolation from measurements made at higher concentrations where the signal-to-noise ratio is good, but broadening due to self-absorption plays a role.     

Numerical study of overpopulation density for laser oscillation in recombining hydrogen plasmas

Overpopulation densities Δn_itij, which are defined as the differences between the population densities per unit statistical weight of the upper and lower excited levels i and j, are calculated as a function of the electron density n_e for various electron temperatures T_e in recombining hydrogen plasmas. Calculation have been made for line pairs with principal quantum numbers (2 ,3), (3, 4) and (4, 5). The effect of the ground-level population density n₁ on Δn_ij is calculated. In this calculation, the atom-atom collision and the self-absorption of the resonance lines are taken into account. The n₁-dependence of Δn_ij remains almost constant until the self-absorption becomes significant. The threshold condition for laser oscillation is discussed in relation to the calculated Δn_ij. Laser oscillation is possible for the line pair (2, 3) at an electron density and temperature higher than for the other pairs (3, 4) and (4, 5) when self-absorption is negligible.     

The reverse shift of the EPR line of paramagnetic centers coupled to species with a fast paramagnetic relaxation

The EPR spectrum of the spin 1/2 paramagnetic centers with a relatively slow relaxation is considered in the case when they are coupled via the Heisenberg exchange interaction to partners which have short times of the longitudinal and transverse paramagnetic relaxation. Under these conditions only the EPR line of paramagnetic centers with a relatively slow relaxation is detectable in experiment. The shape of this line is analyzed by solving numerically kinetic equations for the spin density matrix for simple model systems. Depending on a ratio between the exchange integral and the paramagnetic relaxation rates of partner spins, the EPR line shifts in opposite directions. For moderate relaxation rates, as the relaxation rates decrease, the EPR line shifts toward the gravity center of the total EPR spectrum. In the case of extremely fast relaxation, as the relaxation rates decrease, the reverse shift of the EPR line is expected, the line shifts away from the gravity center of the total EPR spectrum. This type of the non-monotonous line shift was experimentally observed for the monocrystal of [CuNd₂(C₄O₄)₄(H₂O)₁₆] · 2H₂O when relaxation rates were changed by temperature variation.     

The rotationally-resolved absorption spectrum of formaldehyde from 6547 to 6804 cm

The room temperature absorption spectrum of formaldehyde, H₂CO, from 6547 to 6804 cm⁻¹ (1527-1470 nm) is reported with a spectral resolution of 0.001 cm⁻¹. The spectrum was measured using cavity-enhanced absorption spectroscopy (CEAS) and absorption cross-sections were calculated after calibrating the system using known absorption lines of H₂O and CO₂. Several vibrational combination bands occur in this region and give rise to a congested spectrum with over 8000 lines observed. Pressure broadening coefficients in N₂, O₂, and H₂CO are reported for an absorption line at 6780.871 cm⁻¹, and in N₂ for an absorption line at 6684.053 cm⁻¹.     

Spatial and Temporal Characterization of Distilled Water Plasma Using Laser-Induced Breakdown Spectroscopy: Effect of Self-Absorption on Plasma Parameters

The spatiotemporal evolution of the plasma induced by interaction of an Nd-YAG laser pulse with the surface of distilled water is described. The temporal evolution from 200 ns after the plasma creation to 2200 ns of the H _α and H _β lines is reported. Supposing the local thermodynamic equilibrium, the two plasma parameters, electron density and temperature, are determined, including the influence of the self-absorption on its measurements. The spatial evolution of the H _β intensity and of the electron density is given.     

New line intensity measurements for C2H2 around 7.7 μm and HITRAN format line list for applications

Absolute intensities of 467 lines are measured in 9 bands of the 7.7 μm spectral region of the ¹²C₂H₂ molecule, with an average accuracy of 5%. For each band, the vibrational transition dipole moment squared and Herman-Wallis coefficients are obtained in order to model the rotational dependence of the transition dipole moment squared. These results are used to calculate a line list for atmospheric or astrophysical applications. Merged in the line list set up in a previous work for the 8 strongest bands around 7.7 μm [5], these new data give now a quasi-exhaustive view of the ¹²C₂H₂ spectrum in the involved spectral region.     

Microwave study of the submillimeter spectrum of the H2O?HF dimer

The study of the rotational spectrum of the H₂O?HF dimer in the equilibrium gas phase in the range 180-350 GHz by continuously frequency scanning microwave spectrometer with backward-wave oscillator and acoustic detection of absorption is described. The results of analyzing of the most intense spectral series are given. The assignment of some spectral series observed earlier is corrected. Data on the Coriolis interaction between the ground and excited vibrational states are obtained and spectroscopic constants of the dimer are significantly refined.     

Calibration-free laser-induced plasma analysis of a metallic alloy with self-absorption correction

Identification and concentration measurement of constituent elements of a metallic alloy is demonstrated by calibration-free laser-induced breakdown spectroscopy (CF-LIBS) according to a special peak intensity-based model and considering the self-absorption effect. In this procedure, which is based on the line pair ratio method, the effect of line widths, though needs to be theoretically considered, may be approximately ignored. This is mainly true for the multiplet lines, but this property, in the case of some generic spectral lines in a measured spectrum, can be sometimes regarded. Initially, the optical penetration depth and therefrom self-absorption coefficient of each selected spectral line is calculated using the experimental (self-absorbed) intensity of the line. Then, the true (non-self-absorbed) intensity, which is basis of the conventional CF-LIBS calculation, is obtained through a recursive algorithm implemented by the MATLAB programming. In the experimental examination, the recorded spectrum reflects that the metallic alloy is consisted of gold, copper and silver. The concentration of elements is calculated with and without regarding self-absorption correction using 27 trios of spectral lines related to the elements. The average concentrations signify that the measurement error relative to the certified value for the concentration of the gold is modified from 3.56 % in the normal way to 0.34 % after applying self-absorption correction.     

Coherent laser spectroscopy of RF resonances in liquid

Four-photon polarization spectra of double distilled water subjected to a special treatment in a cavitation chamber and 20% aqueous solution of hydrogen peroxide were recorded in the range ±8 cm⁻¹. All recorded spectra contain narrow (< 0.3 cm⁻¹) resonances corresponding to the frequencies of the rotational spectrum of ortho and para spin isomers of the H₂O molecule. Numerical simulation of the spectra obtained made it possible to quantitatively estimate the contribution of the rotational spectrum to the coherent scattering signal. It was found that the contribution of the para spin isomer of the H₂O molecule to the rotational line spectrum decreases in an aqueous solution of the α-chymotrypsin protein. Apparently, this decrease indicates the selectivity of interaction of biopolymer molecules with different spin isomers.     

Line parameters of H2O around 0.8 μm studied by tuneable diode laser spectroscopy

The absorption spectrum of H₂O has been extensively studied over the past decades in the near-infrared and visible regions, but there remain significant discrepancies in the 10,000-12,500 cm⁻¹ range even for the most intense lines. We have studied 24 lines of H₂O using an external-cavity diode laser emitting in the 810-830 nm range, in order to measure absolute line intensities as well as air- and self-broadening coefficients. Comparisons were made with values obtained from the HITRAN database and also with other parameters from recent experiments or predicted calculations. It is suggested that neglecting the effects of H₂O collisional narrowing in radiative transfer calculations of the Earth's atmosphere may have a small but significant impact on the radiative budget of the Earth.     

Generation of supercontinuum radiation in conventional single-mode fibre and its application to broadband absorption spectroscopy

High-pulse-energy supercontinuum radiation with a width exceeding 900 nm in the near-infrared spectral region has been generated in conventional single-mode fibre. The fibre was pumped at 1064 nm which is in the normal dispersion regime, resulting in predominantly red-shifted spectral broadening. Supercontinuum pulse energies exceeding 450 nJ were obtained. The use of conventional fibre allows for inexpensive generation of near-infrared supercontinuum radiation, featuring high pulse energies and good spatial beam quality. This supercontinuum radiation was used to acquire high-resolution (15 pm) broadband absorption spectra of H₂O, C₂H₂ and C₂H₄ in the near-infrared spectral region (1340–1700 nm), using an optical spectrum analyser for detection. H₂O spectra were also recorded at high repetition rates, by dispersing the supercontinuum pulses and detecting the transmitted signal in the time domain. A spectral resolution of 38 pm was obtained employing the dispersed supercontinuum pulses, which is comparable to the H₂O line widths at ambient conditions. PACS 07.07.Df; 42.62.Fi; 42.79.Nv; 42.81.-i     

Line positions and strengths of magnetic dipole transitions of molecular oxygen from stratospheric emission spectra

Submillimeter emission spectra of the low stratosphere (24.5 km) between 30 and 110 cm^-1 have been used to determine line positions and strengths for many of the lines originating in magnetic dipole transitions of the homonuclear molecule O₂. Observed line positions are shown to be in excellent agreement with recently derived theoretical values. Line strengths for these lines, many of which have never been measured in the laboratory, have also been obtained from these spectra. Measurements were made by utilizing the equivalent blackbody envelope defined by the peaks of heavily saturated H₂O lines throughout the spectrum to determine equivalent widths from the O₂ lines. The resulting line strengths are found to be significantly higher than values calculated on the basis of recent theoretical work and, for those lines for which a comparison is possible, higher than previously obtained laboratory determinations. This general feature of the present data is vital not only for the establishment of basic molecular parameters for O₂, but also for the application of recent methods for H₂O and O₃ stratospheric concentration determination in which O₂ lines are used as an internal calibration of the balloon-borne instrumentation.