| |
 |
UNIVERSITY OF BUCHAREST
FACULTY OF PHYSICS Guest
2024-11-22 1:35 |
 |
|
|
|
Conference: Bucharest University Faculty of Physics 2003 Meeting
Section: Optics, Spectroscopy, Plasma and Lasers
Title:
Explanation of selective population of the 2p1 level of neon atoms in the case of M - effect in neon+ hydrogen and neon+oxygen gas mixtures
Authors:
L. Ciobotaru, P. Chiru, G. Musa
Affiliation:
National Institute for Lasers, Plasma and Radiation Physics, Bucharest
E-mail
Keywords:
Abstract:
In a number of previously published papers we reported the possibility of obtaining nearly monochrome radiation spectra using discharges in multiple gas mixtures at pressures in the range 10 ¡V102 torr. This effect of radiation monochromatisation was called the M-effect /1/-/15/.
In order to characterize this effect we introduced the M parameter defined as the ratio of the relative intensities of the radiation of two chosen wavelenghts, here lambda2 = 585.3 nm and lambda2 =614.3 nm, i.e.,
M = I (lambda1=585.3nm )/I (lambda2=614.3 nm) ( 1 )
Using this parameter, various recorded spectra can be compared and the value will be a measure of the the M-effect ¡§intensity¡¨.
Recorded spectra of a narrow gap (0.15 mm) PDP type discharge at 100 torr in Ne +1%Xe and also in (Ne+1%Xe)50%+(H2)50% are presented in figures 1 and 2, respectively.A dramatic change of spectra can be observed.
All these behaviours are closely related to the presence of the negative ions and therefore we concluded that the M-effect is due to the ion-ion recombination, a process wich has a large cross section /16/.
However, the ion-ion recombination can not explain why after the recombination process only the neon level 2p1 is filled while all other levels from 2p2 down to 2 p10 remain less populated.
In the present paper we finally give an explanation of the M-effect including selective population of the (2p1) level of neon .
Let us consider the three body reaction which can be written as:
Ne+ + H- + P Ne*( 2p1) + other products (1)
Where P is the third reacting particle, also in an excited state.
The probability of such a reaction depends strongly on the energy balance between the right and left side of the equation (1), respectively. The probability of reaction (1) will decrease quickly with the increase of the energy deffect ƒ´E.
The probability of Ne+ collisions with H- is high due to the coulombian attractive forces. The density of the hydrogen atoms excited on resonant level at hydrogen partial gas pressures of over a few torr corresponds to the densities of metastable atoms in low temperature plasmas. Indeed, the lifetime of H*(n =2) will be similar to that of the metastable atoms due to the capture of the radiation H at gas pressures higher than 10 torr.
This paper is dedicated to the final explanation of the M-effect.
Let us consider the energy balance for equations (1) . Energy deffect is ¡Ó 0.2 eV.
We must consider also the kinetic energy of negative-pozitive ion, gained due to the coulombian attractive forces.The added energy is arround 0.2 eV for interatomic distance
ra = 60 and 0.5 eV for ra = 26 .
The probability of having such a reaction where all reacting particles are in energetic states above the ground state is high only due to the high cross-section of the ion-ion recombination process. This process compensates the lower concentration of the third colliding particle (in metastable state).
The three-body reaction considered is more efficient ( as observed in our experiments ) at elevated pressures. Heavy particle collisions also explains why the optimum percentages of the gas mixture is arround 50% .
Explanation of the M-effect is now complete for neon+hydrogen and neon+oxygen gas mixtures.
|
|
|
|