Intensity Of Molecular Emission Research Articles

The first molecules in the intergalactic medium and halos of the Dark Ages and Cosmic Dawn

We study the formation and destruction of the first molecules at the epochs of the Dark Ages and Cosmic Dawn to evaluate the luminosity of the protogalaxy clumps (halos) in the molecular lines. The cosmological recombination is described using the RecFast model of an effective three-level atom, while the chemistry of the molecules is examined using the relevant basic kinetic equations. We then studied the effect of collisional and radiative excitation of molecules on the intensity of molecular emission in both warm and hot halos. Using the Planck data on the reionization of the intergalactic medium at z ∼ 6−8, we evaluated the upper limits of the light energy density for four models of thermal light from the first sources that appeared in the Cosmic Dawn epoch. Assuming that in the halos, the light energy density may essentially be even higher, we estimated the impact of the light from the first sources (the first light) on the formation and destruction of the first molecules in them as well as between them. We show that the molecules H2 and HD are destroyed by photodissociation processes shortly before the full reionization in the inter-halo medium, in the medium of both types of halos and for all models of the first light. At the same time, the number density of helium hydride ions, HeH+, shows essentially more complicated dependences on the kinetic temperature of halos and the models of the first light. These features characterizing the abundance of molecules also determine the intensity of the halos luminescence during their evolution. Furthermore, we calculated the evolution of the brightness temperature of the individual halo in the rotational lines of H2, HD and HeH+ molecules relative to the temperature of the cosmic microwave background at redshifts corresponding to the Dark Ages and Cosmic Dawn epochs. It does not exceed the microkelvin, but its detection may be an important source of information about the physical processes taking place at the beginning of the formation of the first stars and galaxies at the epochs of the Dark Ages and Cosmic Dawn.

Imager observation of concentric mesospheric gravity waves over Srinagar, Jammu and Kashmir, India

Using the NARL airglow imager in the Indian subtropical station of Srinagar, Kashmir, India, we report the characteristics of the concentric deformed circular pattern of gravity waves detected at ∼85 km height. OH molecular emission intensities from the height of ∼85 km as observed by the imager in the wide band optical filter of centre wavelength of 840 nm show concentric deformed circular gravity waves drifting northwestward. Using Atmospheric Infrared Sounder (AIRS) image at the centre wavelength of 8.1 µm, deep convective activity around the imager site in the lower atmosphere is recognized as the source mechanism of the observed concentric gravity waves in the mesosphere. The determined phase speed, direction and period of these concentric gravity waves (CGWs) is ∼47 m/s, 150° north of east and ∼10 min (intrinsic period ∼8 min) respectively. At heights of ∼97 km [OI (1S)] and ∼250 km [OI (1D)], these concentric gravity waves are sporadically visible depending on the possible vertical movement of airglow layer height. The dissipated portions of these concentric gravity waves get converted into turbulence at these heights. Using anelastic gravity wave dispersion relation, decreasing horizontal wavelength from the centre of concentric gravity waves is explained. This result is novel in the sense that it disagrees with most of the earlier interpretations of such observations.

Influence of target temperature on AlO emission of femtosecond laser-induced Al plasmas

The influence of the target temperature on the molecular emission of femtosecond laser-induced breakdown spectroscopy (LIBS) was investigated experimentally. An Al target was ablated to produce laser-induced plasma. The Al target was uniformly heated to a maximum of 250 °C. The measured molecular emission was AlO (Δν = 0) from the femtosecond LIBS of the Al target. The measurements indicated that the molecular emission of AlO increased as the temperature of the Al target increased. In addition, a two-temperature model was used to simulate the evolution of the electron and lattice temperature of the Al target with different initial temperatures. The simulated results showed that the electron and lattice temperatures of Al irradiated by the femtosecond laser increased as the initial temperature of the Al target increased; also, the simulated ablated depth increased. Therefore, an increase in the initial Al target temperature resulted in an enhancement in the spectral signal of AlO from the femtosecond LIBS of Al, which was directly related to the increase in the size of the ablated crater. The study suggested that increasing the temperature of the target improves the intensity of molecular emission in femtosecond LIBS.

Influence of distance between target surface and focal point on CN emission of nanosecond laser-induced PMMA plasma in air

Laser-induced breakdown spectroscopy (LIBS) is a technique for spectral composition analysis of materials containing atomic and ionic emission lines, as well as a few molecular emission bands. Here we focused our study on molecular emission from CN (B2∑+→X2∑+) based on LIBS method. Polymethyl methacrylate (PMMA) was ablated by employing a Nd:YAG laser system in air under atmospheric pressure. In the ultraviolet range, the molecular emission intensities of CN violet bands were observed with a spectrometer equipped with an intensified CCD detector. The effect of distance between sample surface and focal point (DTSFP) on the intensities of molecular emission was studied in detail. The results showed that the molecular emission intensities of CN violet bands exhibited a strong dependence on the DTSFP. As the surface of the PMMA sample approached the focal point gradually, the emission intensity of CN increased at first and then dropped down. In addition, vibrational temperature of CN molecule was also calculated. The vibrational temperature showed the similar change in the emission intensity, while the position at the maximum vibrational temperature was inconsistent with the position at the CN intensity.

Effect of lens focusing distance on AlO molecular emission from femtosecond laser-induced aluminum plasma in air

This paper investigated the effect of lens focusing distance (LFD) on optical emission from femtosecond laser-induced breakdown spectroscopy (LIBS) of Al in air. The measurements showed that the emission intensities of Al (I) line and AlO molecular band strongly depended on the LFD. Along with the change in the LFD, two extreme emission intensities appeared in Al (I) line and AlO (0-0). It was due to self-focusing, defocusing, refocusing effects during femtosecond laser propagation in air. That is to say, there were two convergent points. The spectral intensity of Al (I) line at first focus point was higher than that at second focus point. However, the spectral intensity of AlO (0-0) at second focus point was higher compared with that at first focus point. For molecular emission of femtosecond LIBS, the second focus point is more suitable for generation of AlO molecule. In addition, the plasma temperature was also calculated. The temperature at first focus point was higher than that at second focus point. Therefore, the mechanism of weaker molecular emission at first focus point is due to higher plasma temperature. This research will be beneficial to optimize the spectral intensity of molecular emission in the future femtosecond LIBS.

Comparison subpolar mesopause OH(6-2) temperature over Yakutia with the calculated data of NRLMSISE-00 model for 1999-2015

The analysis of changes in temperature of mesopause region based on fluctuation measurements of rotational temperature and intensity of molecular emission of hydroxyl OH (6-2) excited at ∼87 km altitude is presented. Observations were carried out at the Maimaga station (63°N, 129.5°E), at a distance of 120 km to the north from Yakutsk. Measurements were conducted with a digital infrared spectrograph. The temperature was determined from the distribution of the emission intensity in the different branches of the molecular hydroxyl band. Comparison OH(6-2) temperature with the calculated data of NRLMSISE-00 model was defined based on the data received from 1999 to 2015. 2320 midnight temperature values of hydroxyl OH (6-2) suitable for comparison were obtained at the Maimaga station over 16 years of measurements. The NRLMSISE-00 model describes temperature changes at the height of the mesopause region from October to April within the experimental fluctuations with a seasonal temperature variation of ∼ 35 K, deviations from the experimental values are no more than 7 ± 4 K. A correlation analysis was performed to compare the rotational temperature OH (6-2) and the NRLMSISE-00 model calculations. When the number of observations at the station Maimaga more than 180 days (about six months) correlation coefficient R> 0.7. This means that the NRLMSISE-00 model accurately describes the temperature changes of the subauroral mesopause.

Femtosecond Laser-Induced Breakdown Spectroscopy Studies of Nitropyrazoles: The Effect of Varying Nitro Groups.

The technique of femtosecond laser-induced breakdown spectroscopy (FLIBS) was employed to investigate seven explosive molecules of nitropyrazole in three different atmospheres: ambient air, nitrogen, and argon. The FLIBS data illustrated the presence of molecular emissions of cyanide (CN) violet bands, diatomic carbon (C2) Swan bands, and atomic emission lines of C, H, O, and N. To understand the plasma dynamics, the decay times of molecular and atomic emissions were determined from time-resolved spectral data obtained in three atmospheres: air, argon, and nitrogen. The CN decay time was observed to be longest in air, compared to nitrogen and argon atmospheres, for the molecules pyrazole (PY) and 4-nitropyrazole (4-NPY). In the case of C2 emission, the decay time was observed to be the longest in argon, compared to the air and nitrogen environments, for the molecules PY, 4-NPY, and 1-methyl-3,4,5-trinitropyrazole. The intensities of the CN, C2, C, H, O, and N emission lines and various molecular/atomic intensity ratios such as CN/C2, CN(sum)/C2(sum), CN/C, CN(sum)/C, C2/C, C2(sum)/C, (C2 + C) / CN, (C2(sum) + C)/CN(sum), O/H, O/N, and N/H were also deduced from the LIBS spectra obtained in argon atmosphere. A correlation between the observed decay times and molecular emission intensities with respect to the number of nitro groups, the atmospheric nitrogen content, and the oxygen balance of the molecules was investigated. The relationship among the LIBS signal intensity, the molecular/atomic intensity ratios, and the oxygen balance of these organic explosives was also explored.

Analysis of explosive and other organic residues by laser induced breakdown spectroscopy

With the aim of realizing a compact instrument for detection of energetic materials at trace levels, laser induced breakdown spectroscopy was applied on residues from nine explosives in air surroundings. Different potentially interfering organic materials were also analyzed. The residues were not uniformly distributed on an aluminum support and single-shot discrimination was attempted. For a single residue type, large shot-to-shot fluctuations of the line intensity ratios characteristic for organic samples were observed, which made material classification difficult. It was found that both atomic and molecular emission intensities, as well as their ratios, are strongly affected by an amount of the ablated support material, which mainly determines the plasma temperature. With respect to the spectra from the clean support, emission intensities of atomic oxygen and nitrogen are always reduced in the presence of an organic material, even if its molecules contain these elements. This was attributed to chemical reactions in a plasma containing carbon or its fragments. Hydrogen atomic emission depends strongly on the local humidity above the sampled point and its line intensity shows shot to shot variations up to 50%, also on a homogeneous sample. It is argued that shock waves generated by previous spatially and/or temporally close laser pulses blow away a relatively heavy water aerosol, which later diffuses slowly back towards the sampled point. C 2 and CN exhibit a peak emission behavior with atomic Al emission, and their variable ratio indicates an existence of different formation or removal mechanisms from the plasma, depending on the plasma parameters and on the composition of the organic residue. On the basis of these observations, an attempt is made to establish a suitable procedure for data analysis and to determine the optimal experimental conditions, which would allow for discrimination of explosives from other, potentially interfering, residues.

Spatially resolved temperature measurements in a furnace atomization plasma excitation spectrometry source

Spatially resolved atomic emission intensities from helium, and molecular emission intensities from OH and N + 2 have been measured in a furnace atomization plasma excitation spectrometry (FAPES) source. He I emission at 388.86 nm was used to monitor the spatial structure of the plasma in the source while increasing the radio frequency (r.f.) power applied to its center electrode. At higher r.f. power the He I emission intensity increased significantly while its spatial structure remained relatively unchanged. The He I emission was found to be most intense adjacent to the center electrode. Some less intense emission was observed adjacent to the graphite cuvette wall and some very weak emission was seen throughout the volume of the source. These observations suggest that the FAPES source operates as an r.f. glow discharge. Emission intensities from the OH (0-0) rotational A 2 Σ + → X 2 Π i and N + 2 (0-0) rotational B 2 Σ + o → 2 Σ = g bands were used to monitor the effects of increasing the r.f. power applied to the center electrode of the source. From these measurements, rotational temperatures for these molecules were calculated. The intensity measurements showed that there is a significant thermal gradient in the source with OH rotational temperatures ranging between 680 and 1050 K and N + 2 rotational temperatures ranging between 580 and 1920 K with 60 W r.f. power applied to the center electrode. At higher r.f. powers there is an increase in rotational temperatures and an increase in the dissociation of molecular species in the FAPES source. Lead excitation temperatures were calculated using the line ratio method by measuring the emission of the Pb I 280.119 and 283.306 nm lines at different r.f. powers. The temperature was found to increase monotonically with r.f. power over the range of 35 to 75 W.

Binary mobile phases for supercritical fluid chromatography with helium microwave-induced plasma detection

Microwave-induced plasma atomic emission detection is examined for supercritical fluid chromatograpiy detection with binary methanol/ carbon dioxide mobile phases. Spectra are obtained and compared with pure helium plasmas, plasmas with added carbon dioxide, and added binary mobile phases. Trends of molecular emission intensities and species were examined as functions of metianol/carbon dioxide composition ratios and supercritical fluid pressures. Adding carbon dioxide to the pure helium plasma reduced and/or eliminated molecular bands from OH and N 2 + while producing intense bands of CN, C 2 , NH, and N 2

Evaluation of the capacitively coupled helium microwave plasma as an excitation source for the determination of inorganic and organic tin

A capacitively coupled He microwave plasma (He CMP) with a tubular Ta electrode was investigated as an excitation source for atomic emission spectrometry. Spatial distributions of the He plasma support and Sn molecular emission intensities were obtained, and intense atomic emission was found in the plasma centre. The He excitation temperature was almost the same as that of the microwave-induced plasma. Analytical performance was evaluated for the determination of inorganic Sn followed by hydride generation and collection in a cold trap, and also for the speciation and determination of butyltin compounds by interfacing the He CMP with a gas chromatography system. Several experimental parameters were optimised, and the signal to background ratio, signal to noise ratio, reproducibility and limit of detection were obtained in each instance.