Metastable Cross Sections Research Articles

Excitation into5p57plevels from the ground level and theJ=2metastable level of Xe

We present experimental cross-section measurements for electron-impact excitation from the ground level and from the $\text{Xe}(5{p}^{5}6s)\phantom{\rule{0.2em}{0ex}}J=2$ metastable level into levels of the $\text{Xe}(5{p}^{5}7p)$ manifold using the optical method. The magnitudes of cross sections for excitation out of the ground-state range from $(65--365)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}20}\text{ }{\text{cm}}^{2}$. Cross sections out of the ground level are also investigated for pressures ranging from 0.1--1.0 mTorr, and show moderate dependence (particularly at high energies) on pressure due to cascades from resonant levels. Cross sections for excitation out of the metastable level have peak magnitudes that are on average more than an order of magnitude larger than their ground-state counterparts. Furthermore, cross sections out of the metastable levels into the $\text{Xe}(5{p}^{5}7p)$ levels as a function of energy display a surprising variety of shapes which are discussed in relation to oscillator strengths. Together, the ground state and metastable cross sections measured in this work are expected to be useful for optical diagnostics of plasmas containing xenon.

Measurements of cross sections for electron-impact excitation into the metastable levels of argon and number densities of metastable argon atoms.

The technique of laser-induced fluorescence (LIF) has been applied to measure the cross sections for electron-impact excitation into the metastable levels of argon atoms as well as the number densities of the argon metastable atoms produced by electron excitation. A monoenergetic electron beam excites the ground-state atoms into the 3${\mathit{p}}^{5}$4s $^{3}$${\mathit{P}}_{0}$${,}^{3}$${\mathit{P}}_{2}$ metastable levels (1${\mathit{s}}_{3}$ and 1${\mathit{s}}_{5}$ in Paschen's notation) and a pulsed laser pumps the atoms of a metastable level to a level in the 3${\mathit{p}}^{5}$4p configuration (2p in Paschen's notation). The transient LIF from the 2p level is shown to be proportional to the apparent cross section of the metastable level and to the metastable number densities so that measurements of LIF enable us to determine both metastable cross sections and number densities. Methods for absolute calibration are described. We obtain both the apparent and direct excitation cross sections for each of the two metastable levels for electron energies from threshold to 200 eV and the results are compared with previous experimental and theoretical works. The pulsed LIF technique is also used to determine the disappearance rates of the metastable atoms after the electron beam is turned off. Two distinct decay modes are found and the observed behaviors are consistent with calculations based on diffusion theory.

A laser-induced fluorescence study of resonance structure in the electron impact excitation functions of metastable neon and helium

The technique of laser-induced fluorescence (LIF) following electron impact excitation is used to examine the neon 3P0 and 3P2(M/sub /J) and the helium 21S metastable cross sections near threshold. In each case resonance structure is observed. The branching ratio of resonance features into the two neon metastable channels is discussed.

Metastable excitation measurements in CO and N2by high-resolution electron impact, using a low work function detector

High-resolution electron impact has been used to measure the excitation functions of the metastable states in CO and N2. A low work function detector has been used and this has enabled the lowest metastable states of CO and N2, a 3 Pi and A 3 Sigma u+ respectively, to be included in the measurements. This ability to observe the lowest-lying metastable states and the high sensitivity of the measurements has allowed much new structure to be observed in the metastable excitation functions of these molecules. The modified Rydberg formula has been used to obtain tentative classifications of the higher-lying resonances. The measurements also provide information about the shape of the total metastable cross sections in CO and N2.