Damir Veza

Satellite and diffuse bands of the KHg excimer

Abstract We present new spectroscopic evidence on the group of satellite bands in the quasi-static red wing of the potassium resonance lines broadened by mercury. The essential feature of the suggested qualitative model for their interpretation is the existence of an avoided crossing between the B 2 Σ 1 2 + and A 2 Π 1 2 electronic states. In addition to this, a very broad diffuse band with two peaks at about 617 and 624 nm was observed and interpreted as KHg excimer emission from higher excited states.

Interference and diffuse continua in the Rb2 spectrum

Argon-ion laser-induced fluorescence measurements of rubidium vapour have been performed in order to study the quasi-continuum emission of RB2 between 540 and 610 nm. By means of single longitudinal-mode excitations with 476.5 and 488 nm lines the authors found that this quasi-continuum band in the fluorescence spectrum consists of diffuse bands partly overlapped by the interference-type continuum, unresolved in previous experiments. This interference continuum appears at the longer wavelength end of the Stokes emission lines for a certain number of single longitudinal modes of 476.5 and 488 nm laser lines. The authors estimated the ground-state dissociation energy D0 (Rb2X1 Sigma g+)=4180+or-70 cm-1.

Detection limit and selectivity for lithium isotopes in continuous wave field ionization laser spectroscopy

Abstract We report the first analytical measurements of lithium isotopes by Doppler-free continuous-wave field ionization spectroscopy (CW-FILS). This technique combines stepwise laser excitation of analytes to long lived Rydberg states and subsequent ionization in an electric field spatially separated from the laser excitation region. The spatial separation of excitation and field ionization is achieved using a thermal atomic beam. An extrapolated absolute detection limit of about 20 fg for 7 Li and an isotope selectivity better than 4 × 10 13 for 6 Li/ 7 Li are obtained.

Time-resolved spectroscopy of a homogeneous dielectric barrier discharge for soft ionization driven by square wave high voltage

Helium capillary dielectric barrier discharge driven by the square wave-shaped high voltage was investigated spatially and temporally by means of optical emission spectroscopy. The finding of the previous investigation conducted with the sinusoidal-like high voltage was confirmed, i.e., the plasma in the jet and the plasma in the capillary constitute two temporally separated events. The plasma in the jet occurs prior to the discharge in the capillary and exists only during the positive half period of the applied high voltage. The time delay of the capillary discharge with respect to the discharge in the jet depended on the high voltage, and it was between 2.4 and 8.4xa0μs for the voltage amplitude change in the range from 1.96 to 2.31xa0kV, respectively. It was found that, compared to sinusoidal-like voltage, application of the square wave high voltage results with stronger (~6 times) He line emission in the jet, which makes the latter more favorable for efficient soft ionization. The use of the square wave high voltage enabled comparison of the currents (~1xa0mA) flowing in the capillary during the positive and negative high voltage periods, which yielded the estimation for the charge dissipated in the atmosphere ((4u2009±u200920xa0%)u2009×u200910−11xa0C) through the plasma jet.

Atmospheric helium capillary dielectric barrier discharge for soft ionization: broadening of spectral lines, gas temperature and electron number density

The capillary helium dielectric barrier discharge (DBD) operating at atmospheric pressure was investigated by means of optical emission spectroscopy with the aim to determine the dominant broadening mechanism of the helium spectral lines, gas temperature and electron number density. The dependence of emission profiles of helium 388 nm, 501 nm, 587 nm, 667 nm, 706 nm and 728 nm lines on discharge voltage, helium pressure and position along the DBD capillary was investigated. Also, the pressure and voltage dependence of the profiles of hydrogen H-alpha and H-beta lines was examined. The Lorentzian widths of the normalized helium line profiles were found to be constant with respect to the applied voltage and the position along the capillary. The dominant broadening mechanism for all investigated lines was identified to be due to collisions with ground-state helium atoms, with the Stark broadening being negligible. It was determined that the temperature of the gas was constant along the capillary and independent of the voltage applied on the DBD electrodes and that its value coincided with the room temperature. The measurements of the dependence of the Lorentzian width of hydrogen H-alpha and H-beta lines on helium pressure, combined with gas temperature determined in the experiment, yielded the following values for the broadening parameters due to broadening by neutral helium: γνHe(Hα) = 1.56 × 10−9 cm3 s−1 and γνHe(Hβ) = 3.16 × 10−9 cm3 s−1. From the analysis of the measured H-alpha and H-beta line profiles the upper limit of the electron number density in the investigated plasma was obtained as ne ≤ 1.4× 1012 cm−3.

Wave numbers and Ar pressure-induced shifts of 198Hg atomic lines measured by Fourier transform spectroscopy

Wave numbers and argon-pressure-induced shifts of mercury emission lines were measured using a UV/visible Fourier transform spectrometer (FTS). The observations were made with electrodeless lamps containing isotopically pure 198Hg and argon buffer gas at pressures of 33 Pa (1/4 Torr), 400 Pa (3 Torr), 933 Pa (7 Torr) and 1333 Pa (10 Torr). Calibration of the FTS wave number scale was obtained from the four most prominent 198Hg lines (6p 3P2–7s 3S1 at 546.2 nm, 6p 3P1–7s 3S1 at 436 nm, 6p 3P0–7s 3S1 at 404.8 nm and 6p 3P2–6d 3D3 at 365.1 nm), enabling measurements of wave numbers and argon pressure shifts of other UV and visible mercury transitions with high accuracy. Our measurements provide new data for the wave numbers and pressure-induced shifts of 20 mercury lines. The wave numbers of mercury lines emitted from the 400 Pa (3 Torr) lamp can be used as standards for wavelength calibration in inductively coupled plasma (ICP) spectrochemical analysis or in experiments where medium-resolution monochromators are used. The pressure-induced shifts of the 198Hg emission lines are in reasonable agreement with theoretical predictions and could be of interest for validating calculations of mercury–argon interactions.

Atmospheric Helium Capillary Dielectric Barrier Discharge for Soft Ionization: Determination of Atom Number Densities in the Lowest Excited and Metastable States

The populations of the lowest excited helium states 2s 3S1, 2s 1S, 2p 3P0 J, and 2p 1P0 created in an atmospheric helium capillary dielectric barrier discharge were determined by means of optical emission spectroscopy. The emitted intensities of 388, 501, 587, and 667 nm lines were measured side-on and end-on with respect to the discharge axis. The comparison of optically thin side-on spectra with end-on spectra, which exhibited the absorption effects in the line kernels, enabled the determination of the average values of the number densities n1 in the considered He states along the plasma length L. The field of the theoretical profiles for a series of the n1L parameters pertinent to the experimental conditions was calculated for each line. By introducing the experimental data into the field of calculated curves, n1L corresponding to the particular state could be obtained. The measurements of the emission profiles were done as a function of the discharge voltage in the range covering homogeneous as well as filamentary DBD operation mode. Due to nonuniformity of the excited atom density distribution along the plasma, the values of n1 could be obtained only in the homogeneous operation mode where the nonuniformity was small. The following maximum values were found for the number densities in the investigated states: n1 av (2s 3S1) = (2.9 ± 1.1) × 1013 cm−3, n1 av (2s 1S) = (1.4 ± 0.5) × 1013 cm−3, n1 av (2p 3P0 J) = (1.1 ± 0.4) × 1013 cm−3, n1 av (2p 1P0) = (4.2 ± 1.6) × 1012 cm−3, and they represent the average populations along the plasma column in the capillary.

Pseudosonic wave detection in laser spectrometry

Abstract Frequency changes of plasma oscillations in the kHz range (pseudosonic waves) induced by resonant laser excitation of species in low-pressure dc discharges are used for detection of 21 Ne in pure Ne. The analytical capability and the limitations of this novel spectrochemical technique have been studied in noble gas discharges.

An experimental study on the influence of trace impurities on ionization of atmospheric noble gas dielectric barrier discharges.

While the influence of trace impurities in noble gas discharges is well established in theoretical work, experimental approaches are difficult. Particularly the effects of trace concentrations of N2 on He discharges are complicated to investigate due to the fact that for He 5.0 the purity of He is only 99.999%. This corresponds to a residual concentration of 10 ppm, thereof 3 ppm of N2, in He. Matters are made difficult by the fact that He DBD plasmajets are normally operated under an ambient atmosphere, which has a high abundance of N2. This work tackles these problems from two sides. The first approach is to operate a DBD plasmajet under a quasi-controlled He atmosphere, therefore diminishing the effect of atmospheric N2 and making a defined contamination with N2 possible. The second approach is using Ar as the operating gas and introducing propane (C3H8) as a suitable substitute impurity like N2 in He. As will be shown both discharges in either He or Ar, with their respective impurity show the same qualitative behaviour.

Time- and spatially resolved emission spectroscopy of the dielectric barrier discharge for soft ionization sustained by a quasi-sinusoidal high voltage

AbstractA helium capillary dielectric barrier discharge was investigated by means of time-resolved optical emission spectroscopy with the aim of elucidating the process of the formation of the plasma jet. The helium emission line at 706xa0nm was utilized to monitor spatial and temporal propagation of the excitation of helium atoms. The discharge was sustained with quasi-sinusoidal high voltage, and the temporal evolution of the helium atomic emission was measured simultaneously with the discharge current. The spatial development of the plasma was investigated along the discharge axis in the whole region, which covers the positions in the capillary between the electrodes as well as the plasma jet outside the capillary. The high voltage electrode was placed 2xa0mm from the capillary orifice, and the distance between the ground and high voltage electrode was 10xa0mm. The complete spatiotemporal grid of the development of the helium excitation has shown that during the positive half-period of the applied voltage, two independent plasmas, separated in time, are formed. First, the early plasma that constitutes the plasma jet is formed, while the discharge in the capillary follows subsequently. In the early plasma, the helium atom excitation propagation starts in the vicinity of the high voltage electrode and departs from the capillary towards the ground electrode as well as several millimeters outside ofxa0the capillary in the form of the plasma jet. After relatively slow propagation of the early plasma in the capillary and the jet, the second plasma starts between the electrodes. During the negative voltage period, only the plasma in the capillary between the electrodes occurs.n Graphical AbstractSpatiotemporal evolution of the helium excitation propagation in the He capillary DBD