“…σ (E e ) is the apparent cross section of the relevant electron impact process. The cross sections for excitation from the ground state and transition from metastable states to the 2p levels have been measured [14,15]. If the EEDF is assumed to be Maxwellian, then ln g p is linear with E e , and (2) turns out to be…”
Section: Resultsmentioning
confidence: 99%
“…Here, the definition of r is given by (5). In (11), the second term on the right-hand side of (7) has been neglected because the cross section of the excitation from 1s 3 is much smaller than that from 1s 5 [15] and the population of 1s 3 is approximately a factor of five less than the population of 1s 5 atoms. From (11), it can be found that the emission at 640.2 nm can be divided into two parts: excitations from the ground state and the 1s 5 level, and that is the reason why the light intensity at 640.2 nm shows a typical bi-exponential decay in the afterglow.…”
Experimental results of time-resolved optical emission intensities of atomic neon lines (585.2 and 640.2 nm) in a pulsed, low pressure (10–95 mTorr) inductively coupled afterglow neon plasma are presented. It is found that the light intensity at 585.2 nm decays exponentially but at 640.2 nm shows a typical bi-exponential decay after the rf power is turned off. Since the population of these two excited levels is generated by inelastic collisions between electrons and atomic neon (1s5 metastable and ground state), the evolution of these two emission lines can also be estimated by a simple collisional–radiative (CR) model which uses time-dependent results of EEPF and the concentration of 1s5 atoms, both of which can be measured by using optical absorption techniques and a Langmuir probe. It is found that the measured evolution of the emission intensity at 640.2 nm has an excellent agreement with that from the model, over a long time interval after the rf power is turned off (from 20 to 150 µs), as long as the measured EEPF is used instead of an assumed Maxwellian.
“…σ (E e ) is the apparent cross section of the relevant electron impact process. The cross sections for excitation from the ground state and transition from metastable states to the 2p levels have been measured [14,15]. If the EEDF is assumed to be Maxwellian, then ln g p is linear with E e , and (2) turns out to be…”
Section: Resultsmentioning
confidence: 99%
“…Here, the definition of r is given by (5). In (11), the second term on the right-hand side of (7) has been neglected because the cross section of the excitation from 1s 3 is much smaller than that from 1s 5 [15] and the population of 1s 3 is approximately a factor of five less than the population of 1s 5 atoms. From (11), it can be found that the emission at 640.2 nm can be divided into two parts: excitations from the ground state and the 1s 5 level, and that is the reason why the light intensity at 640.2 nm shows a typical bi-exponential decay in the afterglow.…”
Experimental results of time-resolved optical emission intensities of atomic neon lines (585.2 and 640.2 nm) in a pulsed, low pressure (10–95 mTorr) inductively coupled afterglow neon plasma are presented. It is found that the light intensity at 585.2 nm decays exponentially but at 640.2 nm shows a typical bi-exponential decay after the rf power is turned off. Since the population of these two excited levels is generated by inelastic collisions between electrons and atomic neon (1s5 metastable and ground state), the evolution of these two emission lines can also be estimated by a simple collisional–radiative (CR) model which uses time-dependent results of EEPF and the concentration of 1s5 atoms, both of which can be measured by using optical absorption techniques and a Langmuir probe. It is found that the measured evolution of the emission intensity at 640.2 nm has an excellent agreement with that from the model, over a long time interval after the rf power is turned off (from 20 to 150 µs), as long as the measured EEPF is used instead of an assumed Maxwellian.
“…1b , examples from electron-impact excitation are presented. Specifically, the recommended values of the (1s-2p) cross-section for atomic hydrogen 16 are displayed together with a lognormal fit ( R 2 > 0.996) as well as measurements 17 for excitation out of the neon metastable level ( R 2 > 0.96). Examples of molecular dissociation into neutral metastable fragments are illustrated in Fig.…”
Section: Resultsmentioning
confidence: 99%
“… Figure 1 Ionization, excitation and dissociation by electron impact: comparison of measurements with lognormal fits (R 2 values in the legends). ( a ) Ionization : inert (He, Ne, Ar, Kr, Xe) 12 and 2 nd row atoms (C, N, O 13 ; F 14 ); ( b ) Excitation : H 16 and Ne 17 ; ( c ) Dissociation of H 2 O into O( 1 S) 18 and OH(X) 19 fragments. The cross section for O( 1 S) has been multiplied by a factor of 100 to aid comparison.…”
Quantum physics is undoubtedly the most successful theory of the microscopic world, yet the complexities which arise in applying it even to simple atomic and molecular systems render the description of basic collision probabilities a formidable task. For this reason, approximations are often employed, the validity of which may be restricted to given energy regimes and/or targets and/or projectiles. Now we have found that the lognormal function, widely used for the probability distribution of macroscopic stochastic events (as diverse as periods of incubation of and recovery from diseases, size of grains, abundance of species, fluctuations in economic quantities, etc.) may also be employed to describe the energy dependence of inelastic collisions at the quantum level (including ionization, electron capture and excitation by electrons, positrons, protons, antiprotons, etc.), by allowing for the relevant threshold energy. A physical interpretation is discussed in this article by analogy with the heat capacity of few-level systems in solid state physics. We find the generality of the analysis to extend also to nuclear reactions. As well as aiding the description of collision probabilities for quantum systems, this finding is expected to impact also on the fundamental understanding of the interface between the classical and quantum domains.
“…The difficulties of preparing a metastable-atom target for laboratory collision experiments and the necessity of detecting very low-level excitation signals have made these measurements particularly challenging. With the development of new techniques, cross sections for excitation out of metastable levels have been reported for He, Ne, Ar, and experiments for Kr are underway [1][2][3]. In this paper we focus our attention primarily on Ar.…”
Methods for measuring cross sections for electron-impact excitation into the 2p levels (Paschen's notation) out of the metastable levels of argon are described. The results of the cross sections and their relation to the corresponding cross sections for excitation out of the ground state are explained by a multi-pole field model. Applications to plasma diagnostics are discussed.
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