Molecular Line Intensities Research Articles

RF plasma investigations for plasma-assisted MBE growth of (Ga,In)(As,N) materials

We have investigated N incorporation in Ga(As,N) grown by radio frequency (RF) plasma-assisted molecular beam epitaxy in a wide range of N 2 flow rate and RF power. Atomic and molecular emission line intensities of nitrogen plasma have been measured by optical spectroscopy. For low N 2 flow rates, the reactive nitrogen species that mostly incorporate are nitrogen atoms whereas for higher flow rates excited molecular nitrogen incorporation seems to prevail. For low N 2 flow rates, the N density in the plasma has been related to excited atomic and molecular species emission lines, leading to the determination of the dissociation rate which was found to increase above 0.6 for high RF powers. Finally, impurities related to the N source have been detected in Ga(As,N), especially oxygen, responsible for non-radiative recombination centres, whose atomic emission line has been identified in the plasma emission spectrum. These results are crucial to further control N incorporation in (Ga,In)(As,N) materials and improve crystal quality.

Influence of N-O chemistry on the radiative emission from a direct current nitrogen plasma jet

In this work we have studied experimentally the influence of N-O chemistry on radiative emissions from a small DC plasma torch at 1 atm. The plasma torch has been designed for the atomizer of an on-line atomic absorption spectrometer, which is used for the detection of vaporized metals in various process gas flows. The plasma torch was burning in pure nitrogen and an oxygen bearing sample gas was introduced into the plasma jet. The temperature of the plasma jet was determined spectroscopically to be around 2000 K. At this temperature the equilibrium UV radiation of excited atoms or molecules is negligible, but molecules and atoms are effectively excited by collisions with metastable nitrogen molecules formed in the plasma. The emission spectra of the plasma jet were measured in the wavelength range 200-400 nm in various gas mixtures. In pure nitrogen the second positive system of N2was observed, the intensity of which exceeded the estimated radiation at thermal equilibrium even by 1013 times. With a trace amount of oxygen-containing species, such as O2, CO2 or H2O, very intense γ-band radiation of NO was observed. The intensities of the lines were calculated to be around 109 times greater than corresponding equilibrium intensities. High intensities were also observed in atomic resonance lines of several metals. The intensity of the Cu line at 324.75 nm was 5×103 higher than the estimated equilibrium emission at given conditions. Correspondingly, the emission intensity of Pb line at 283.3 nm was around 5×105 and Cd line at 228.8 nm around 2×107 times more intense than at thermal equilibrium. Our study indicated that the rate of the collisional excitation of metal atoms by metastable nitrogen molecules was roughly the same for all the studied metals. When larger amounts of O2 or H2O were introduced into the plasma jet, the emission intensity of molecular lines and atomic lines of metals decreased drastically. We showed that radiative emissions do not interfere with absorption measurements provided that the percentage of O2 in the plasma jet is above 5 vol% or of water vapour above 2 vol%.

Experimental study of a supersonic low-pressure nitrogen plasma jet

A supersonic nitrogen arc plasma jet expanded in a low-pressure test chamber is studied. Radial measurements of temperatures and densities are performed in the expanding region over various sections from the nozzle exit. Nitrogen is highly dissociated in the arc chamber and the plasma is far from equilibrium. Electron temperature and density, as well as gas velocity, are measured by means of parallel and crossed electrostatic probes. Measurements of selected atomic and molecular line intensities are performed in the 250–850 nm spectral range to obtain number densities of various N2, N2+ and N excited levels. The rotationally resolved emission spectrum from the (0–0) band of the N2+ first negative system (B2Σ+u→X2Σ+g) is analyzed and compared to synthetic spectra to evaluate the rotational temperature within the flow field. The kinetic scheme of ionic recombination of N+ and N2+ is examined. A recombination path of the N2(C3Πu) electronic state via the N2(C″5Πu) state is proposed for the N(2D0)+N(4S0) nitrogen recombination.

Ratios of molecular hydrogen line intensities in shocked gas - Evidence for cooling zones

Column densities of molecular hydrogen have been calculated from 19 infrared vibration-rotation and pure rotational line intensities measured at peak 1 of the Orion molecular outflow. The run of column density with energy level is similar to a simple coolng zone model of the line-emitting region, but is not well fitted by predictions of C-shock models current in the literature.

Spectroscopic analysis of independent discharges in molecular gases

The schematic of the feed system and the structure of the discharge device is described in detail in [5]. The geometric dimensions of the discharge region are 2.7  4  40 cm. Preliminary ionization is achieved with the radiation of spark discharges positioned beyond a grid anode. The voltage on the capacitor can vary over the range of 12-35 kV. The discharge device allows one to obtain a volumetric discharge in COs, N2, He, and in their mixtures for the pressures of (0.i-i)'i0 s Pa. The spectra are recorded with an ST~-I spectrograph. It is necessary to have 25-100 pulses for normal darkening of the RF-3 photographic film (depending on the conditions of the experiment). The behavior of the intensity of individual molecular bands and spectral lines over time is observed with an MDR-2 monochromator, F~U-39 (or FEU-79) photomultiplier, and a dual-beam $8-2 oscillograph. Simultaneous recording of the signal with the F~U and the voltage pulse in the discharge enables one to determine the time at which the discharge pulse is formed in the spectrum of one or another line. The dimensions of the discharge region in the direction of the optical axes of the monochromator and the objective of the spectrograph are equal to 4 and 40 cm, respectively. A miniature image of the discharge region is projected onto an input slit in the spectrograph perpendicular to the plane of the electrodes. This method of measurement allows one to obtain intensity distributions for the recorded spectral lines in the direction of the anode-cathode [4] and, when the image is rotated by 90 ~ , in the direction perpendicular to the direction of the voltage of the electric field. In order to eliminate the illumination of regions pertaining to the cross section of the discharge region under investigation, a system of slotted diaphragms is used. An additional mirror is used for taking into account the optical depth of the plasma for vibrational transitions when conducting relative measurements of the excited states of the molecules. A qualitative analysis of the spectrograms for discharges in pure gases of C02, N2,

24MgH+ in the solar photospheric spectrum

The24MgH+ (A1Σ+ −X1Σ+) molecular lines have been identified in the photospheric spectrum. The rotational excitation temperature determined from the analysis of molecular line intensities of24MgH+ is found to be of the order of 4850 K which corresponds to the photospheric temperature of the Sun. The CNDO/2 dipole moments of24MgH+ for internuclear distance range: (1.3–2.1) A in theX1Σ+ state can be approximated byM(R)=4.92+1.33R. Estimations for the spontaneous emission Einstein coefficients (Av′ v″) and the absorption oscillator strengths (fv′ v″) for the (1, 0), (2, 0), and (2, 1) transitions in theX1Σ+ state of the24MgH+ ion are also made.

Determination of the rotational excitation temperature in solar type stars

The OH molecular spectrum has been identified in three solar type stars, β Com, β CVn, and κ Cet. The rotational excitation temperature from molecular line intensities of OH has been determined for these stars. The observations in high resolution were made by use of the IUE satellite.

Molecular orbitals and line intensities in the X-ray photoelectron spectrum of ClO −4

The Gelius—Siegbahn model for calculating cross sections for photoionization of electrons from molecular orbitals is discussed and a new method for determining atomic orbital cross sections is indicated. As an illustration the X-ray photoelectron spectrum of ClO − 4 in LiClO 4 is compared with that of O 2− in MgO and Cl − in LiCl.