Silicon ions are normally detected at altitudes above 100 km and within sporadic E layers. Traces have rarely been observed within the more permanent metallic layer near 93 km. This is surprising since silicon is an important constituent of chondritic meteorites, which ablate material in this region to provide a primary source of the metallic species observed there. Evidence is presented that Si(+)ions form SiO2(+) at the lower altitudes, and exist in this ionic state prior to recombination. A rocket launched from El Arenosillo, Spain on 3 July 1972, at 0743 LMT, during the predicted period of the Beta Taurids meteor shower, passed through a continuous belt of metallic ions that began near 85 km, ended near 115 km, and exhibited an order of magnitude increase in the form of a layer near 114 km. Si(+)was measured in and below the ledge down to 103 km. It showed a rapid decrease below this height. Radiative association is offered as a primary mechanism for SiO2(+) production

Goldberg, R. A.

English

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SILICON IONS BELOW 100 KM:
A, CASE FORO Si2
'(NASA-Tt-X-70751) SILICON IONS BELOW 100 N74-32790
km: A CASE FOR Si02(+) (NASA) 14 p HC
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Preprint
SILICON IONS BELOW 100 KM: A CASE FOR SiO2+
Richard A. Goldberg
Upper Atmosphere Branch
August 1974
GODDARD SPACE FLIGHT CENTER
Greenbelt, Maryland
SILICON IONS BELOW 100 KM: A CASE FOR SiO2 +
Richard A. Goldberg
Upper Atmosphere Branch
ABSTRACT
Silicon ions are normally detected at altitudes above 100 km and within
sporadic E layers. Traces have rarely been observed within the more
permanent metallic layer near 93 km. This is surprising since silicon
is an important constituent of chondritic meteorites, which ablate mate-
rial in this region to provide a primary source of the metallic species
observed there. In this work, we present evidence that Si + ions form
SiO 2 + at the lower altitudes, and exist in this ionic state prior to re-
combination. A rocket launched from El Arenosillo, Spain on 3 July
1972, at 0743 LMT (X = 57. 10), during the predicted period of the (
Taurids meteor shower, passed through a continuous belt of metallic
ions that began near 85 km, ended near 115 km, and exhibited an order
of magnitude increase in the form of a layer near 114 km. Si was
measured in and below the ledge down to 103 km. It showed a rapid
decrease below this height. A comparison of the isotopic ratio for
nickel, [ 6 0 Ni] / [58 Ni ),with the measured ions shows too large a ratio
for the ions below 100 km, suggesting contribution to 60 + from other
sources. A prime candidate is SiO 2+ , since Si + is observed to de-
crease in the region where the ratio becomes too large. No evidence
for SiO + (44 ) is present in the data, indicating that Si+ forms SiO2+
either directly or through SiO+ in a short lived state. Radiative
association is offered as a primary mechanism for SiO 2 + production and
yields a calculated reaction rate of 2 x 10- cm secI .
iii
PRECEDING PAGE BLANK NOT LM
ILLUSTRATIONS
Figure Page
1 Two observed distributions of positive ion species in the
daytime lower thermosphere over Thumba, India on 19
March 1970, illustrating the metallic layer near 93 km . . . . 6
2 Observed distribution of positive ion species in the lower
thermosphere over El Arenosillo, Spain during the 3
Taurids meteor shower on 3 July 1972. .... . . . . .. 7
3 Relative number abundances of ions (NASA 14.483 rocket
data) and neutral elements (chrondritic and crustal data)
normalized to Si + , Si = 100 ...... .......... 8
4 Comparison of measured ratio [60+]/[ 58 + ] to the known ratio
[60 Ni]/[ 58 Ni ] for nickel isotopes . . ..... . . . . . . 9
5 Comparison of the measured ratio ( [25 + ] + [26+ ] )/ [ 24 +] to
the known ratio ( [25Mg + [2 6Mg )/ [ 24Mg] for magnesium
isotopes ...................... 
...... 10
iv
SILICON IONS BELOW 100 KM: A CASE FOR SiO2+
by Richard A. Goldberg
Numerous rocket-borne mass spectrometric measurements of ion composition
in the upper atmosphere have defined a metallic ion belt between 90 and 95 kilo-
meters as a reasonably permanent feature independent of location and time
(e. g. Young et al, 1967; Narcisi 1967; Johannessen and Krankowsky, 1972;
Aikin and Goldberg, 1973). Figure 1 illustrates this layer as observed at the
daytime equator by Aikin and Goldberg (1973). The data have shown the domi-
nant species within the layer to be Fe + and Mg with reduced quantities of Na+,
Al +, K, Ca +, Ni + , and other metal ions. These constituents are believed to be
principally of extraterrestrial origin, deposited at these altitudes by meteoric
ablation. The remainder must be terrestrial, precipitated by natural and arti-
ficial processes. A thorough knowledge of the species' abundances can thereby
provide information concerning structure and evolution of certain extraterrestrial
bodies such as comets, and simultaneously assist study of the transport processes
responsible for bringing trace constituents of terrestrial origin into the upper
atmosphere.
Ion-neutral chemistry plays a critical role in analyzing this problem, especially
since most of the rocket measurements to date have only provided ion informa-
tion. Silicon is a semi-metallic constituent that must be important because of
its high abundance. in meteoric materials (e. g. Mason, 1971) yet as an ion it is
distributed in a manner unexplainable in terms of its known chemistry. Above
100 km and primarily within the confines of mid and high latitude sporadic E(Es)
layers, metal ions are observed to dominate the ion structure (Istomin, 1963;
Young et al, 1967; Narcisi, 1967; Goldberg & Aikin, 1973) and here Si+ is usually
observed to be an important, if not dominant atomic ion. However, within the
permanent metallic ion layer below 95 km, Si + has rarely been observed. The
ion-neutral chemistry of silicon must therefore be unique, to permit its exis-
tence in a free ionic state above but not below 100 km. This work is concerned
with an investigation of this problem, made possible by the study of an unusual
metal ion structure recently observed during a meteor shower event.
The region between the permanent metallic ion layer near 95 km and the Es
layers above 100 km does not normally exhibit significant metallic ion structure
except during specific events such as a meteor shower. An example is that of
Goldberg and Aikin (1973), illustrated in Figure 2. These results were obtained
during the P Taurids meteor shower on July 3, 1972 at 0743 LMT (X = 57. 10)
with a rocket-borne quadrupole ion mass spectrometer launched from El
Arenosillo, Spain. Absolute ion magnitudes were obtained by normalization
procedures, using the measured total electron and ion densities determined by
1
Faraday rotation radio wave propagation and Gerdien probe experiments aboard
the same flight.
These data exhibit an Es peak near 114 km. The metal ions dominating this
peak are Fe + (56+), Si + (28+), and Mg+(24+). Identification of 28 + as N2 + is not
feasible because of the difficulty in explaining the presence of a short lived
molecular constituent within the peaked distribution. Here, the only constituents
present should be metal atomic ions, since only these possess sufficiently long
lifetimes to permit transport mechanisms to redistribute them into the narrow
ledge observed. Above the ledge, 28 + takes on the chemical equilibrium dis-
tribution predicted for N, +.
Under the metal ion ledge, metallic ions are observed in abundance to altitudes
below 93 km, the region where meteoric ablation is maximum. Si + is observed
to rapidly decay below 102 km, and at 93 km is a very minor atomic ion. The
high abundance of metallic ions between 95 and 105 km has also been observed by
Narcisi et al (1972) during a polar cap absorption (PCA) event and by Zbinden
et al (1973) during the Geminid meteor shower. Both results display a similar
profile for 28 +.
Figure 3 represents the relative number abundances of the metal ion species
when normalized to 28 + as silicon. The results within the layer are compared
to those obtained near 101 km. These results are further compared with the
neutral relative number abundances measured for the same constituents in
chondritic and crustal materials (converted from the weight abundances given
in Ahrens, 1965). The agreements obtained demonstrate the validity for iden-
tifying 28 + as Si + within and below the metallic ledge, and suggest most species
observed to be of extraterrestrial origin.
The rapid depletion of Si + below 100 km and its minor contribution within the
primary metallic layer shows the Si + chemistry to be more complicated than
that of the more common metallic constituents, e. g. Fe + and Mg +. As noted
by Brown (1973) in his recent review on metallic ion chemistry in the upper
atmosphere, production processes for Si + are not significantly different than for
other metal ions, unless silicon ablates from meteorites in a unique form cur-
rently unspecified. If we turn to loss processes for an explanation of the unique
Si' distribution, we must consider oxides (e. g. SiO + , SiO 2 +) since dissociative
recombination of these constituents is far more rapid than radiative recombina-
tion of Si +.
Information concerning SiO 2 +is available in the data of 14.483. SiO 2 + (60 +) has
the same mass as the nickel isotope 6 0 Ni+. By comparing the known isotopic
ratio of [ 6 0 Ni] /[ 5 8Ni] to the measured ratio of [60 + ] /[ 58 + ], as shown in
2
Figure 4, we find a trend leading to values well in excess of the nickel ratio
below 105 km, thereby suggesting a second contribution to 60+ (e. g. SiO2+).
This is of interest because the 60+ enhancement occurs at the very location
where Si+ begins to deplete.
The reader is cautioned to note that this result has been extracted from data
obtained near the sensitivity limit of the instrument. This also accounts for
the absence of data points below 100 km, where 60+ was not clearly discern-
able. Figure 5 offers a comparative plot for the measured ratios of ([ 2 5 + ] +
[ 2 6+] )/ [ 24+ ] as referenced to the known relative abundance of the magnesium
isotopes. In this case the scatter of measured data is tightly bound to the
theoretical line throughout the entire altitude range where measurement was
possible. This result is offered to demonstrate the scatter expected, and lend
credence to the [60 + ]/[ 58 + ] curve.
If, in fact, the data does provide a measurement of SiO2+ , then we arrive at a
magnitude of 2 cm-3 near 100 km. Swider (1969) has suggested SiO 2 formation
by the process.Si+ + 02 N2SiO2+ N2 with a rate coefficient ki = 10-30 cm6
sec: . This would then be followed by dissociative recombination SiO2+ + e
Si + O, with a rate k 2 = 3 x 10-7 cm 3 sec-1 . An equilibrium value for SiO2 +
of 0. 1 cm-3 is calculated for 100 km, suggesting need of a larger value for
k1 /k 2 than that used. On the other hand, assuming Swider's numbers to be
correct, this low value for SiO 2+ implies that either 60+ contains an additional
unknown component, or that another SiO 2+ source is present. If we postulate
this source to be the product of radiative association, i. e. Si+ + 02 -f SiO2
+ + h,
then we calculate a rate k 3 of 2 x 10-16 cm 3 sec-1 for this process.
The above equilibrium system seems feasible since Fehsenfeld (1969) has
found SiO + + O -- Si+ + O, to be exothermic, implying that SiO + production.
through the reverse process is not likely. The absence of SiO + (44+) within the
metallic ion region observed on this rocket flight, or for that matter, in any
other metallic ion data obtained by this observer, appears to concur with the
laboratory result.
In conclusion, we -have interpreted an excess abundance of 60+ ions measured
near 100 km to be caused by the presence of SiO 2+. The results, although
somewhat marginal due to the sensitivity restrictions of the detector, appear
valid. Furthermore, the unusual metallic ion distribution present on the day
of the measurement provided a unique opportunity for the silicon problem to be
studied. The results suggest that below 100 km Si+ is rapidly depleted by two
and three body reactions with 0,, forming SiO2+ which then recombines.
Further measurements under similar conditions should be conducted to deter-
mine the validity of the results suggested here, especially to establish the
importance of radiative association, which has a reaction rate too small for
laboratory verification.
3
REFERENCES
Ahrens, L. H. (1965) Distribution of the Elements in Our Planets, p. 97,
McGraw-Hill, New York.
Aikin, A. C. and R. A. Goldberg (1973) Metallic Ions in the Equatorial Iono-
sphere, J. Geophys. Res., 78, 734-745.
Brown, T. L. (1973) The Chemistry of Metallic Elements in the Ionosphere
and Mesosphere, Chem. Rev., 73, 645-667.
Fehsenfeld, F. C. (1969) Si + and SiO+ Reactions of Atmospheric Importance,
Canadian J. Chem., 47, 1808-1809.
Goldberg, R. A. and A. C. Aikin (1973) Comet Encke: Meteor Metallic Ion
Identification by Mass Spectrometer, Science, 180, 294-296.
Istomin, V. G. (1963) Ions of Extraterrestrial Origin in the Earth's Ionosphere,
Space Research, 3, 209-220.
Johannessen, A. and D. Krankowsky (1972) Positive-ion Composition Measure-
ment in the Upper Mesosphere and Lower Thermosphere at a High Latitude
During Summer, J. Geophys. Res., 77, 2888-2901.
Mason, B. (1971) Introduction in Handbook of Elemental Abundances in Meteorites
ed. by B. Mason, Gordon and Breach Science Publishers, New York.
Narcisi, R. S. (1967) Processes Associated with Metal-ion Layers in the E
Region of the Ionosphere, Space Research, 8, 360-369.
Narcisi, R. S., C. R. Philbrick, D. M. Thomas, A. D. Bailey, L. E. Wlodyka,
D. Baker, G. Frederico, R. Wlodyka, and M. E. Gardner (1972) Positive
Ion Composition of the D and E Regions During a PCA in Proceedings of
COSPAR Symposium on Solar Particle Event of November 1969 ed. by J. C.
Ulwick, REP. AFCRL-72-0474, Air Force Cambridge Research Labora-
tories, Bedford, Massachusetts.
Swider, W., Jr. (1969) Processes for Meteoric Elements in the E Region Planet.
Space Sci., 17, 1233-1246.
Young, J. M., C. Y. Johnson and J. C. Holmes (1967), Positive Ion Composi-
tion of a Temperature Latitude Sporadic E Layer as Observed During a
Rocket Flight, J. Geophys. Res., 72, 1473-1479.
4
Zbinden, P. A., M. A. Hidalgo, P. Eberhardt, and J. Geiss (1973), Positive
Ion Composition in the Lower Ionosphere During the Geminid Meteor Shower
and the Occurrence of a Winter Anomaly, paper presented at the 16th
Plenary Meeting of COSPAR, Konstanz, May, 1973.
5
125 ' '" " I I I I l I , 1 l[ I I II I fi, l
6UPLEG G32 30 Ni
40 23 2 8 16
120- NASA 14.425 39 .24
THUMBA, INDIA _.-
8:27 LMT - 23 NASA 14.424
MARCH 19, 1970 NASA 14.424
115 X=53.2' 2 THUMBA, INDIA
23 ------ Na+
-- 10:17 LMT
- 24 *--+ Mg 1
- - + MARCH 19, 1970
27 --- Al2- " X = 27.8"
110 28--- Si+,N 2
+  >24- 30 
... NO+
- 32a 02 16 16 - 0'A
E 39- K+ 40 23-----Na
40 - Ca+  27 23 24 - -Mg +
- 56 ----- Fe+  27 --- Al'
- Ni - TOTAL IONS 24 28--Si+ N2 +6 )L 30 ----- NO
39 1 23 A 28 32-O +
100- 40 2+ 307 2 39 -K
27 40 -Ca
- -L - -56 --- Fe+
"~*~ - N - TOTAL
95- 1, -IONS
56 -.. . 28 ;'23ST 16 1 24 32 30 N,
90 -/ 1 23. f
-,56
- . d . 39 & 
39 56 p40
L j 28 -
100 101 102 103 104 105 10-1  100 101 102 103 104 105 106
ION DENSITY (cm-3 ) ION DENSITY (cm-3 )
Figure 1. Two observed distributions of positive ion species in the daytime lower thermosphere
over Thumba, India on 19 March 1970, illustrating the metallic layer near 93 km.
24 14 28 '16 N
K 56 1 32
120 , 32
45
124 28115 . . ....... ..... 24
....... 
5658
3 9. 5 8 . .... .
339 3-o--
/1
23 2 Na
O D28 NSI
Sr30 i--- NwO-
4 45 ---- Sc+
1 -52 ----o Cr Ni
058 " "56 --- Fe "
24 , I
105
23 NASA 14.483 N2+,Si+
900 NO+
SJULY 3, 1972 -02+
407:43 LMT XCa+=57.1
58 4056 56Fe+
85 - 24-(
100 101 102 103 104 NASA 14.483
EION DENSITY (cm - 3 ) ARENOSILLO, SPAIN
shower on 3 July 1972.
7
ION ABUNDANCES NEUTRAL ABUNDANCES
NASA 14.483 (AHRENS, 1965)
ELEMENT 101 km 114 km CHONDRITES CRUST
Na 12 9.1 4.6 10.4
Mg 49 57 93.5 8.0
Si 100 100 100 100
K 0.81 0.38 0.37 5.3
Ca 3.6 1.2 5.5 10.4
Sc 1.0 0.35 0.003 0.005
Cr 3.4 1.77 0.92 0.02
Fe 149 158 70.9 10.0
Ni 4.2 4.7 3.6 0.13
Figure 3. Relative number abundances of ions (NASA 14.483 rocket data) and neutral elements
(chrondritic and crustal data) normalized to Si+ , Si = 100.
RELATIVE ABUNDANCE
115
X
x NASA 14.483
x
x [60Ni]/[58NI]
x
110 x
x
x
x
x
105 xE
x
M XI-t.
100-
95-
90
0 0.2 0.4 0.6 0.8 1.0
o60 5]/[8 + ]
Figure 4. Comparison of measured ratio [60+ ]/
[58+1 to the known ratio [6 0 Nil / [" Nil
for nickel isotopes.
9
RELATIVE ABUNDANCE
115 0
x
x
X
x NASA 14.483
110 x
[25Mg] + [26Mg1
X [24 Mg
x
105E x
W x
I--
I--
x
100-
X
X
x UPLEG
x
o DOWNLEG
95 x
90 I I
0 0.2 0.4 0.6 0.8 1.0
([25 +] + [26 +] )/[24+]
Figure 5. Comparison of the measured ratio
([25 +] + [26+] )/ [24 + ] to the known
ratio ([ 2 5 Mg] + [2Mg])/[2 4 Mg]
for magnesium isotopes.
10


Silicon ions below 100 km: A case for SiO2(+)

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