Ground-state Ne Atoms Research Articles

Quenching of [formula omitted] and [formula omitted] states by collisions with [formula omitted] atoms

The cross sections and rate constants for quenching 4 He(2 1 S) , 4 He(2 1 P) , 3 He(2 1 S) and 3 He(2 1 P) states by collisions with ground state Ne atoms are measured by a time-resolved method in a He–Ne electron beam excited plasma at low pressure. These rate constants at T g =600 K are: k 4 He(2 1 S) =(1.6±0.2)×10 −10 , k 4 He(2 1 P) =(3.4±2.5)×10 −10 , k 3 He(2 1 S) =(1.6±0.2)×10 −10 and k 3 He(2 1 P) =(5.7±1.2)×10 −10 cm 3 s −1 . The cross sections derived from the rate constant are σ 4 He(2 1 S) =(8.4±0.8)×10 −16 , σ 4 He(2 1 P) =(1.8±1.3)×10 −15 , σ 3 He(2 1 S) =(7.1±0.9)×10 −16 and σ 3 He(2 1 P) =(2.6±0.5)×10 −15 cm 2 , respectively. The diffusion coefficient of 3 He(2 1 S) in 3 He is estimated to be D 3 He(2 1 S)− 3 He =1.9D 4 He(2 1 S)− 4 He , based on comparison with 4 He . A time-dependent collisional radiative model for an e-beam sustained He–Ne plasma is developed and the predicted line intensity of NeI λ=6328 A ̊ line is compared with the experimental data. The influence of different processes involved in population and depopulation dynamics of He(2 1 S) state are evaluated.

Potential energy curves and dipole transition moments to the ground state of the system Ar*(3p54s, 3P, 1P)+Ne

Relativistic core-potential calculations have been carried out on Ω states resulting from the interaction of Ar*(3p54s, 3P, 1P) with ground state Ne atoms. The results yield the correct asymptotic limits for the atomic states of Ar while shallow minima (700–800 cm−1) at large internuclear distances, 7–8 bohr, are obtained for the excited states. Dipole transition moments between pairs of states have been calculated and strong radiative transitions are predicted from excited states to the ground state. The 1(I) state, correlating with the metastable P23 state of Ar is found to have a small dipole transition moment at short and intermediate nuclear distances leading to a radiative lifetime for this state of 8.3 μs.

Exciton Self-Trapping and Lattice Defect Creation in Rare Gas Solids and Other Insulators

We have studied the possible creation of stable lattice defects induced by exciton self–trapping (STE) in solid neon. Generally speaking, the STE–bubbles accompanied with a plastic deformation are found to be at lower energies than a pure STE–bubble. Those with two vacancies in the first atomic shell have the lowest energy. Some of the vacancy–interstitial atom pairs escaped mutual annihilation as the electronic sub–system returned to the ground state, thereby stable lattice defects resulted. The emission energy changes of lattice defect–associated STE have been evaluated and are found to be in reasonable agreement with observed data. Much has been learned recently on the role of the STE in radiation damage creation of ionic halides. We have made a brief comparison of the ionization induced defect formation processes in the two types of materials. In both cases, the excited electron is the prime driver of the process. In solid neon the excited electron is directly attracted to the localized hole on Ne, but repelled by the ground state Ne atoms. In the halides the excited electron is attracted to the Madelung potential at an anion site instead. In rare gas solids, the Frenkel pair is a purely structural defect in the lattice with the electronic subsystem in its ground state. In ionic halides, the pair of F center and H center is not only an interstitial atom–vacancy pair in the halogen sublattice, but also represents an electronically excited state. Because of this difference the way the created Frenkel defects are stabilized in the two types of material is distinct.

Electron excitation cross sections for the metastable and resonant levels of Ne(2p53s).

The electron excitation cross section both for the $^{3}\mathrm{P}_{2}$ and $^{3}\mathrm{P}_{0}$ metastable levels (1${s}_{5}$ and 1${s}_{3}$ in Paschen's notation) and for the mixed $^{3}\mathrm{P}_{1}$ and $^{1}\mathrm{P}_{1}$ resonant levels (1${s}_{4}$ and 1${s}_{2}$ in Paschen's notation) of the 2${p}^{5}$3s configuration of Ne have been measured. Apparent and direct excitation cross sections are reported for incident electron energies from threshold to 300 eV and are compared with results of different methods of measurements. Ground-state Ne atoms are excited by a monoenergetic electron beam to the 1s levels, and atoms in the 1s levels are pumped to the 2p levels of the 2${p}^{5}$3p configuration by means of a cw dye laser. The laser-induced fluorescence from the 2p level is utilized to determine the electron excitation cross section for the 1s level. Methods for absolute calibration of the cross sections are given.

Optical pumping of the 2p 53s 3P 0 State of 21Ne ( [formula omitted]): g factor and metastability exchange cross section

A C.W. multi-mode dye laser is used to obtain by optical pumping an orientation of the 2p 5 3s 3P 0 ( F = 3 2 ) state of 21Ne. A magnetic resonance experiment leads to the measurement of the g factor g ( 3 P 0) = 3.027 (8) × 10 −4 to be compared with the theoretical prediction (3.025(6) × 10 −4). One obtains also the metastability exchange cross section σ( 3 P 0) = 18.4 ± 4 A ̊ 2 for collisions between metastable ( 3P 0) Ne atoms and ground state Ne atoms. This result is compared with other measurements and theoretical evaluation.

Theory of inelastic collisions between low-lying excited- and ground-state Ne atoms

A quantum-mechanical study of low-energy inelastic collisions of excited- and ground-state Ne atoms has been undertaken. Close-coupling calculations of cross sections for the transitions $^{1}P_{1}\ensuremath{\rightarrow}^{3}P_{1}$, $^{1}P_{1}\ensuremath{\rightarrow}^{3}P_{2}$, $^{3}P_{1}\ensuremath{\rightarrow}^{3}P_{2}$, and $^{3}P_{0}\ensuremath{\rightarrow}^{3}P_{2}$ have been performed at collision energies below 3 eV. All cross sections exhibit a rapid falloff at low energies, reflecting barriers and repulsive walls present in the potential curves. Spin-orbit coupling is assumed to be the transition mechanism. Comparison with experimental data suggests that neglected rotational coupling might be important for some of the quite weak transitions at energies below about 0.1 eV.

Differential scattering of metastable neon on neon

Differential elastic scattering cross sections for a beam of metastable neon (Ne*) incident on ground-state Ne atoms have been measured in the centre-of-mass energy range 7-53 eV. Two peaks identified as rainbow maxima were observed at tau =E theta approximately=45 and 67 eV deg. Oscillatory structure identified as coherent scattering on a gerade-ungerade (g-u) pair of potential curves was also observed. Use of the calculated potentials of Cohen and Schneider (1974) and a semiclassical theory for g-u oscillations allows observed features in the cross section to be attributed to particular molecular states, but difficulties due to complicated interference between scattering on the relevant potentials preclude any unique determination of improved potentials without supplementary information.

Lens testing and construction

The cross sections and rate constants for quenching 4He(21S), 4He(21P), 3He(21S) and 3He(21P) states by collisions with ground state Ne atoms are measured by a time-resolved method in a He–Ne electron beam excited plasma at low pressure. These rate constants at Tg=600K are: k4He(21S)=(1.6±0.2)×10−10, k4He(21P)=(3.4±2.5)×10−10, k3He(21S)=(1.6±0.2)×10−10 and k3He(21P)=(5.7±1.2)×10−10cm3s−1. The cross sections derived from the rate constant are σ4He(21S)=(8.4±0.8)×10−16, σ4He(21P)=(1.8±1.3)×10−15, σ3He(21S)=(7.1±0.9)×10−16 and σ3He(21P)=(2.6±0.5)×10−15cm2, respectively. The diffusion coefficient of 3He(21S) in 3He is estimated to be D3He(21S)−3He=1.9D4He(21S)−4He, based on comparison with 4He. A time-dependent collisional radiative model for an e-beam sustained He–Ne plasma is developed and the predicted line intensity of NeI λ=6328Å line is compared with the experimental data. The influence of different processes involved in population and depopulation dynamics of He(21S) state are evaluated.