D.B. Kokh

Absolute calibration of the efficiency of a VUV-monochromator/detector system in the range 110 - 450 nm

For determining the efficiency of a vacuum-UV monochromator with a multiplier type PMT-142 in the range 110 - 450 nm two different methods for absolute and six methods for relative calibrations were used. The results of all relative calibrations except for one agree to within an accuracy close to the experimental error in the range of their mutual overlap. The accuracies of the relative efficiency curves were found to be 18, 14, 7, 3, 6 and 10% for the ranges 110 - 120, 120 - 140, 140 - 250, 250 - 350, 350 - 400, and 400 - 450 nm, respectively. Absolute calibrations were performed at 147 and nm with an accuracy of 8% in both cases. The differences in the grating illuminations at the monochromator applications and in the calibration were taken into account. The influences of the accuracies of all operations necessary for the absolute calibration on the overall calibration error were thoroughly analysed. If there are significant differences between the geometries of the system illumination during calibration and during application, they may be the main source of error.

Spectroscopic determination of the cold electron population in very low pressure ECR discharges in N2/He mixtures

We describe a spectroscopic study of the electron distribution functions (EDFs) in two types of electron cyclotron resonance (ECR) discharges at very low pressure: a discharge in a simple magnetic mirror trap (ECRD) and a discharge in a sheared minimum-B-trap used as ion source for multiply charged ions (ECRIS). The discharges were run in mixtures of helium and nitrogen at about 7?mPa. Special attention was paid to electrons with kinetic energies below 10?eV. Their contributions were attained by a quantitative analysis of the vibrational structures in the emission spectra of nitrogen, the analysis of processes of step-wise excitation or an analysis of the rotational populations of nitrogen. The models for evaluating the EDFs are discussed in detail. Besides collision processes in the volume of the discharge processes occurring at the chamber walls contribute significantly to the particle balance and are included in the model. In all cases considered low energy electrons contribute more than 90% to the electron population of the discharges. For every discharge EDFs are measured for two benchmark conditions at low and high discharge power. For the ECRIS other conditions are covered by a measurement of the plasma potential, which turned out to be below 30?V for the conditions considered. This low value is a good indicator for the presence of low energy electrons. The plasma potential was obtained from a retarding field analysis of the energy of ion beams extracted from the plasma.Besides the EDFs, our study yields insight into the important collision and wall processes in these low-pressure discharges, including the first observation of rotational cooling of desorbing N2 molecules in an ECRIS.

A comparative study of the electron distribution function in the positive columns in and /He dc glow discharges by optical spectroscopy and probes

We compare to the probe method a spectroscopic method for determining in plasmas the electron distribution function (EDF) over a wide energy range. For a test of the radiative-collisional model we use to describe the plasma radiation, the measured vibrational distributions of (C-B) and (B-X) were compared with calculated ones using our model and EDFs measured by Langmuir probes. From this comparison we obtain a value for the rate constant for vibrational relaxation at the walls. In a second step we invert the system of model equations for obtaining the EDF from measured line intensities. From the vibrational structure of the emission spectra of the nitrogen molecule the EDF is obtained in the energy range of 1.5-4.5 eV. From the relative intensities of the emission of nitrogen molecules and helium atoms the EDF for electron energies above 11 eV is derived. In the region between these ranges the EDF is interpolated. The results agree within the limits of the experimental errors with the EDF measured directly by the probe.

Study of the covalent and triplet ionic-pairing states of the fluorine molecule with the MRDCI method

The results of nonempirical calculations of the electronic structure, spectroscopic constants, and potential-energy curves for the covalent and triplet ionic-pairing states of the F2 molecule are presented. It is shown that the covalent 13Πu state is weakly bound, with the depth of the potential well of this state being of about 0.05–0.2 eV. The effect of the spin-orbital interaction on the ionic-pairing states, which can result in the perturbation of the Ω=0+ and Ω=1 components of the 3Σu− and 3Πu states, is analyzed. It is demonstrated that the lasing observed at λ ≈ 157 nm is caused by the transitions between the ionic-pairing state 23Πg and the weakly bound covalent state 13Πu.

SPECTROSCOPIC DETERMINATION OF COLD ELECTRONS IN ELECTRON CYCLOTRON RESONANCE DISCHARGES WITH HIGHLY CHARGED IONS

A spectroscopic method based on the analysis of molecular and atomic spectra of nitrogen was used for the determination of electron distribution functions (EDFs) in electron cyclotron resonance (ECR) discharges run in nitrogen. EDFs were determined for the plasma region seen by the VUV-monochromator. This region includes the hot core plasma surrounded by a less dense and not so hot halo plasma. The EDF between 1.5 and 4.5 eV was determined from the vibrational distribution of excited molecular states of nitrogen, and that in the energy range above 8.5 eV was evaluated from the intensities of different emission lines and bands of NI and N2. The shape of the EDF in the energy range between 4.5 and 8.5 eV was interpolated by using the electron density measured with Langmuir probes and normalizing the EDF to the same density. Due to the low gas pressure of 2×10−5 Torr vibrational relaxation processes on the discharge chamber wall had to be taken into account. In the wavelengths range 30–400 nm the emission sp...

Electric dipole moment function of the beta 1(3P2)toA 1 3Pi transition in ICl

The optical-optical double-resonance technique has been used for measurements of emission spectra from separate vibrational levels of the 1(3P2) state of ICl (v´ = 12 and 14) populated via the A 1 3 state. The electric dipole moment function of the A transition has been determined over the range of the internuclear distance of 0.29-0.39 nm by means of simulation of the emission spectra from the state.