Electron impact effect on solar C0 molecule destructio

Sarychev, A. P.

Sitnik, G. V.

English

NASA Technical Reports Server

13 
National A e r o n a u t i c s  and Space Administration 
Goddard Space"Pl5ght C e n t e r  
Contract No.NAS-5-12487 
C 
ST -SP -ACH -10794 
THE ROLE OF ELECTRON IMPACT IN THE DESTCTION 
OF CARBON MONOXIDE MOLECULES ON T 
-. A. P .  Saryehev 
& G. F. Sitnik 
(USSR) 
8 JANUARY 1969 
https://ntrs.nasa.gov/search.jsp?R=19690006181 2020-03-12T08:21:29+00:00Z
ST-SP-ACH- 10794 
THE ROLE OF ELECTRON IMPACT IN THE DESTRUCTION 
OF CARBON MONOXIDE MOLECULES ON THE SUN* 
Astronomicheskiy Zhurnal 
Tom 45, No.6, 1303-1305 
Izdatel'stvo "NAUKA", 1968 
I 
by A. P. Sarychev 
& G. F. Sitnik 
SUMMARY 
The rate is estimated of carbon monoxide (CO) molecule dissociation 
by electron impacts in the upper layers of the solar photosphere on the 
basis of the results of experiments on the collision of electrons with mole- 
cules obtained in [ 2 - 4 1 .  Comparison of this rate with those of photodisso- 
ciation and dissociation at collisions with hydrogen atoms, computed in [l], 
shows that the electron collision plays practically no significant role in 
the destruction of CO molecules on the Sun. 
* 
* *  
Analysis is pursued in this paper of mechanisms of CO molecules' decay 
in the transitional layer between the Sun's photosphere and chromosphere. 
elementary processeso:CO destruction were investigated in [ 13 : the thermal dis- 
sociation at collisions with hydrogen atoms and the photodissociation. 
established by way of comparison of these reaction rates that dissociation at 
radiation absorption is somewhat more effective that the decay under the influ- 
ence of hydrogen atom impacts. Besides photons and hydrogen atoms, free elec- 
trons are also part of actively acting components of solar atmosphere on mole- 
cules. The present work is devoted to ascertaining the role of electron impact 
in the destruction of CO molecules on the Sun. 
Two 
It was 
The dissociation of molecules into neutral atoms as well as ions can be 
the result of inelastic collisions of electrons with molecules. In experiments 
on dissociation into atoms one is compelled to meet with difficulties in de- 
tecting andidentifying the neutral products of the reaction, but the dissociative 
*ROL' ELEKTRONNOGO TJDARA V RAZRUSHENII MOLEKUL CO NA SOLNTSE 
2 
ionization is quite successfully studied by the method of retarding (counter) 
potential and the method of mass-spectrography. In particular, the following 
processes are revealed during the bombardment of carbon monoxide by electrons 
(the numerals standing to the left show the minimum kinetic energy required 
for reaction onset) [2, 31: 
9.6 ev CO + e -+ C + O'Y 
20.9 ev CO + e -+ C+ + 0' + e, 
22.8 ev 
23.2 ev 
60 + e -+ C" + 0 + 2e, 
CO f e -+ C' + O+ + e. 
It is easy to see that among the above written four reactions, the first 
is the most advantageous. 
capture of the electron by CO molecule, has been investigated in detail by 
Schultz [4]. 
he succeeded in determining the effective capture cross section d as a function 
of electron's kinetic energy E. The dependence d(E)  has a peak, characteristic 
in form for resonance processes, whereupon the maximum value, 
is reached at E = 10.1 ev. The knowledge of d(E)  allows us to compute the rate 
of CO dissociation by means of electron capture, or, to be mqre precise, the 
reaction rate factor a, entering into law of reagents' concentration variation, 
is 
This reaction, which is the process of dissociative 
In the aggregate of careful experiments with an electron beam, 
CT = 1.6 lo-'' cm2 
--  a N ( C O ) N ( e ) ,  dll' ( C O )  
dt 
where N(C0) and N(e) are respectively rhe concentrations of CO molecules and 
electrons, is the time. If we assume the Maxwellian distribution of electrons 
by velocities and consider that the velocities of molecules are negligibly small 
by comparison with those of electrons, we have 
E 
IiT 
W 
a =4(2nrn,)-''2(kT)-'/* i E o ( E ) c x p  (-- - - )dE;  
0 
(5) 
me being the mass of the electron, T -the temperature and - k the Boltzmann cons- 
tant. Substituting the values of U(E)  from the graph of [l] into formula (5) 
and integrating numerically for T = 5000°K, we found the rate of CO molecules' 
decay as a consequence of reaction (1) in conditions of molecular layer of the 
3 
photosphere: 
We shall now show that the destruction of CO in the photosphere as a con- 
sequence of reactions (2) - (4) is insignificant by comparison with reaction 
(1). 
trons having energies much higher than the thermal energy, that is, of the 
"tai1"'of Maxwellian.distribution. For the temperature of T - 5000°K, the mean 
energy of electron's therma; motion constitutes only /2 kT = 0.65 w ,  while the 
initial potentials of the reactions are respectively E(1) = 9.6 ev, E(2)  = 20.9 
ev, E(3) = 22.8 ev, E(4) = 23.2 ev. The sharp curtailing, according to the 
Maxwell law, of the number of reacting electrons at transition from the disso- 
ciation threshold according to scheme (1) to threshold of (2) - (4), may be only 
This stems from the fact of the participation in reactions only of elec- 
3 
compensated by 
that reactions 
than the cross 
the increase of effective cross sectioss. For examples, in order 
(1) and (2) be identical, the cross section ~ ( 2 )  must be greater 
section a(1) - an2 by 
~ 
-N- 4 2 )  E(1) E ( 2 ) - E ( 1 )  M 10'' 
o ( l )  - E(.))  c's" I; 1' 
times (the given estimate is obtained from the condition of equality for these 
reactions of the values of a, determined by formula (5); for simplicity we 
considered here the cross sections as independent of the energy of the electron 
when the latter exceeds the dissociation threshold). Since there is no basis 
of any kind for expecting in reactlons (2) - (4) such high values of 6, we are 
compelled to recognize the dissociative capture of the electron (1) as the pre- 
dominant dissociation mechanism with molecule CO ionization in the photosphere. 
With respect to molecule CO dissociation by electron impact into neutral 
atoms 
C O + e + C + O + e  (7) 
direct data are not available. However, the small probability of process (7) 
may be qualitatively forecast by utilizing an analogy between 60 and N, mole- 
cules. These molecules are isoelectronic and quite similar in their physical 
properties. But, inasmuch as at N, bombardment by electrons the dissociation 
into neutral atoms was not experimentally observed [2], we conclude that the 
reaction (7) itself is apparently little probable. 
4 
Thus, wehave discussedall the pdssible variants of CO dissociation by. 
electron impact and ascertained that in conditions of molecular photosphere 
layer, the moSt active will be the dissociation by way of electron captuke. 
Therefore, the ra-te of reaction (l), provided by formula (a), will be close 
to the aggregate rate of CO decay under the action of collisions with electrons. 
In order to compare the rate of CO dissociation by electron impact with the 
photodissociation rates computed in 111: 
and the dissociations at collisions with hydrogen atoms: 
we shall substitute i n  formula (6) the value of electron concentration 
N(e) Z 10l2 cmW3 
in the region of the molecular layer 
= - 2.7. IQ-8N(CO) sec"' . 
e 
As may be seen from relations (8) - (lo), for one act of CO destruction 
by electron impact corresponds on the average about 
4.0 io--" 
I. A, dlr2 
2.7 ' 20-8 
acts of destruction by atomic hydrogen impacts and 
photodissociation acts. Consequently, in conditions of transition layer bet- 
ween the photosphere and chromosphere of the Sun the electron impact plays no 
practically noticeable role in the destruction of CO molecules. 
The Shternberg's State 
Astronomical Institute 
Received on 21 May 1968 
References follow. . / 
ST - SP - ACH - 10794 
REFERENCES 
5 
1. G. F. SITNIK, M. CH. PANDE. Astronom. Zh. - 44, 732, 1967 
2. H. S. MASSEY & E. H. S. BURHOP. Electronic and Ionic Impact Phenomena. 
3. 
4. G. J .  SCHULZ, Phys. Rev. 128, 178, 1962. 
London, 1952. 
J. 'D. CRAGGS & H. S. W. MASSEY. Handb. Physik, - 37, 314, 1959. 
CONTRACT No.NAS-5-12487 
VOLT INFORMATION SCIENCES, INC. 
1145 - 19th St.NW 
WASHINGTON D.C. 20036. 
Tel : 223-6700 (X-36) 
Translated by ANDRE L. BRICHANT 
on 8 January 1969 


The role of electron impact in the destruction of carbon monoxide molecules on the sun

Abstract

Similar works

Full text

Available Versions

NASA Technical Reports Server