AFCRL-64- 948

Ionospheric Research

Contract AF19(628)-4014

Scientific Report

on

"Ionospheric Processes and Nitric Oxide"

by

Marcel Nicolet

December 20, 1964

Scientific Report No. 228

(Project 5710, 8605, Task 860502)

"The research reported in this document has been sponsored by theAir Force Cambridgtc Research Laboratories, Office of AerospaceResearch, Bedford, Massachusetts under Contract AF19(628)-4014and, in part, by the National Science Foundation under Grant GP-2914.

"This research sponsored by Defense Atomic Support Agency,Waahington, D. C. , under Sub-Task 7.0010,

Ionosphcre Rcsearch Laboratory

Approved for Distribution

A. H. Waynaick, Directot, 1. R. L.

The Pennsylvania State University

College of Engineering

Department of Electrical Engineering

Table of Contents

Page

Abstract ................ .............................

1. Introduction ................. ........................ 1

2. Ionic Reactions and Ionization Equilibrium . . . . 3

3. Nitric Oxide and Atomic Nitrogen ......... ............ 7

4. Ionospheric Conditions in Various Ionospheric Layers 10

5. Total Production of Nitric Oxide ............. 15

6. Nitric Oxide and the Airglow Continuum ........... .... 20

7. Conclusions ................. ........................ 23

References ................... .......................... 25

ABSTRACT

Analysis of ionic processes in the ionosphere leads to the

conclusion that nitric oxide and its ior are produced by a reaction

between nitrogen molecules and molecular oxygen ions. Such a

process implies a substantial increase of nitric oxide in the E layer

to a value greater than the photochemical concentration. In the lower

N+ + ions produced by cosmic rays are transformedD egon 2 an 2

into NO+ ions. A quantitative estimate shows that these concLusions

are consistent with observational data in the chemosphere and

ionosphere and also suggests the explanation of the night airglow

continuum.

__ _ -P 111 • - - I -"

1. Introduction

The theory of the origin oi the D "egion in L., ,rest ial

ionosphere proposed'by Nicolet and Aikin [19601 indicates that it results,

in its lower part, from cosmic rays ionizing molecular oxygen and

nitrogen and from solar Lyrman-a' ionizing nitric oxide during quiet

solar conditions. The contribution of solar X-rays at wave-lengths

less than 10 A depends on solar activity. The minimum-to-maximum

variation of intensity is a factor of several hundred in the 2-8 A band

[Friedman, 19631. Recent observations by Aikin et al. [19641

definitely show that the role of the 2-10 A band is unimportant for

sufficiently quiet solar conditions. The X-ray effect occurs for the

slightly disturbed sun ard is predominant during flare conditions.

However, if the origin of the normal D region is well known,

the problem of its structure is far from being understood due to the

lack of information concerning its ionic composition The vertical

distribution of its electronic and ionic densities is only approximately

known [Bourdeau, 1Q62; Belrose. 1964; Sagalyn az~d Smiddy. 19641

Consequently, the present knowledge of the daytime and night-time D

region still depends on the theoretical investigations of the physical

processes involving positive and negative ions

An excellent analysis of the present knowledge made recently by

Reid r19641 shows how the role of negative ions is important. The

uncertainty concerning the extent to which laboratory measurements can

be applied to the formation of the D region is clearly seen in a review of

the negative ion reactions by Branscomb [1964). It appears, however,

that the presence of only one ion, namely 02 , subject to photodetachment

by visible radiation is not sufficient to explain the behavior of the D

region. The existence of NO2 which has an electron affinity of 92 kcal

[Farragher et al., 19641, corresponding to photodetachment by

ultraviolet radiation, is almost certain since it can be formed from a

reaction with any atomic negative ion, or by reaction with nitric oxide

as follows:

NO + 0 2 NO? + O + 82 kcal.

A recent discussion of the various positive and negative ionic

processes by Whitten and Popoff [19641 shows how ambiguities may

arise from the use of arbitrary rate coefficients to explain ionospheric

data. Nevertheless, it appears difficult to avoid the conclusion that the

dissuciative recombination at room temperature for diatomic ions is of- 7 3 -1

the order of 10 cm sec Thus, Biondi [19641 gives

.7 3 -1 7 -2.# (2 O. 5) 0. 5). x 10 0 cm "sec

(2.8 * 0. 5) x 10 cm sec a = (2.0 * 0.5) x cm secN2

Taking an average value of the dissociative recombination

coefficient aD - 2 x 10 cm sec for all diat,'mic ions may give the

correct order of magnitude of electron-ion recombination rate

coefficients. Better precision cannot be claimed from an analysis of

aeronomic processes without an exact knowledge of the vertical distribu-

tion of electrons and ions. As far as mutual neutralization resulting from

ion-ion recombination is concerned, a value of the same order

Ci= 2 x 10-7 cm 3sec' for 0 + + 0 and NO + NO 2 may be adopted2 22-8l 3 -1

without any experimental evidence. Other values such as a 10 cm sec

may be possible but a very precise aeronomic study of the lower D region,

-3

which is produced by cosmic rays, is needed in order to determine the

effective recombination of positive ions.

The problem of charge transfer and ion-atom interchange

processes remains in a state of confusion. At the present time, using

laboratory measurements to obtairk aeronomic estimates of rate

coefficients is not a sufficiently accurate approach. N'-ny experimental

determinations do not as yet yield even order of magnitude values.

The purpose of the present paper is not, however, to review all

the information a'•dilable from laboratory experiments and aei-...:iic

calculations, but to consider certain new aspects of the problem of

nitric oxide production and related ionospheric studies The analyses

of recent spectrometric observations by Barth [19641 of nitric oxide and

the mass-spectronmetric studies by Narcissiarnd Bailey [19641 involving

only nitric oxide ions without molecular oxygen ions in the lower part of

the D region require a different method of approach. In view of the

importance of chemical reactions in the analysis of such problems,

reference is made to another paper Nicolet [1964].

2. Ionic Reactions and Ionization Equilibrium

The various ionic reactions have been recently consiwered

[Nicolet and Swider, 1963) and Fig. 1 gives a general idea of the

relationships between the various processes. Only the NO+ ion disappears

by dissociative recombination alone, while 0+ and N+ are subject to2 2

ion-atom interchange reactions or to charge transfer processes,

respectively. The atomic ion 0 is transformed into molecular ions by

ion-atom interchange reactions. The essential exothermic processes

-4-

which are considered here are as follows-

(,Y1 ) ; 0( 4S) + N 2( 1) NO+ ( 1 ) + N( 4S) + 25 kcal (1)

(y 2 ) ;O+(4S) +O 2 ( 3 Zq) 2 1 O(3P) + 35 kcal (2)

(y 3 ) ;O+(4S) + NO(I2r) N0( + + O( 3P) + 100 kcal (la)

4y4 ) ; 0+(4S) + NO( 2) -i O(2 ), + N( 4S) + 4 kcal (2a)

(25 ) ;O 2 1() + NO( 2T) NO + M-'O2(3 V + 45 kcal (3)

(Y6).;+O222H) + N( 4 S) NO+(I E) + 0(3 P) + ql kcal (4)

(-Y7 + ; 2 2) + N1 NO(+IT) + NO(2H) + 16 kcai (5)

+2 3 +41

(y 8 ); N 2 (7) + O( P) 0 +(4 i + N2 ( T) +45 kcal (6 a)+Y 3 +2 1

(y 9 ) ; N2( 2) + 02 ') '0( ) + N.'( I ) + RI kcal (6b)

Reactions (1) and (5) producing NO+ (v' < 3) and NO+ (v % 2),

respectively, may correspond to luminescent reactions Av I I near

4. 3k,. Av = 2 near 2.15, and Av - 3 near 1i,

The loss processes (1) and (2) of 0+ are the only ones ti, be

considered, and their rate coefficients V, and y, are about10 1 • -1 .+

cm sec Reaction (5) is a loss process of O with a low

-l *l 1 -1rate coefficidnt for which we adopt "7 10 cItl SeC rhe loss

rate of 0 by such a procesb is certainly negligible in the F layers, hut

cannot be neglected in the lower ionosphere [Nicolet and Swider. 1 9631.

It may compete with the dissociative recombination.

00) ; O +e - ' + 0 (7)0

NITRIC OXIDE REACTIONS

CHEMOSPHERE

NO + h v - I --O N +-O~NO

N * O(+M)-h I NO (+M) -) h h

1

N -NO - 0 + N,

IONOSPHERE

NO- h' -NO -e -NO NO N O

I i INO N N

4- 4-

1 I/0) h 0) 0-.0-

I I0) NO

/ NN+C+/- NO. 4N0 -0NO(

{00 " - 04 N0 4 1S•4,N;, N NO÷1•

"•14 "8

0,0

"N N "0 N" +"NO + rl)

N,~ ~ ~~+ NO + NO +N • ,•O ,!€ - N÷

• * NO} - "1) NO + N IV÷•r)

0 0""N - 0 0 NO+ ({

NN N "+ i""N N NO NO )

N I..I- ,-

-6-

which leads to oxygen atoms in 3P, ID and 1S states.

As far as the charge transfers (6) are concerned, they are+

ri..pid enough to be the essential loss processes of N in the D a-ad E

regions. The dibscciatlve recombination process

(a N2 + e -- N' + N" , .8)

which may lead to nitroge., atoms in 4S, 2D and 2P states, is relatiely

important only in the F region.

The dissociative recombination of NO+

(aNO) ; NO+ + e - N' + 0' (9)

is the only loss proceas of this ion. It may give nitrogen atoms in 4S

atd 2D states and oxygen atoms in 3P and 1 D states.

An order of magnitude, at sufficiently low temperatures, for the

dissociative recombination coefficient such as

"aD = a"N2 = O2 = 'NO " 2 x 10 cm 3 sec -1 (10)

is only a sufficient approximation for illustrative purposes. A precise

aeroncrmic study requires a precision better than 20 percent.

The negative ions of first importance are the molecular ions 02

and NO 2 which must occur in the lower D region. A (not precise) value

for the recombination coefficient with positive ions can be obtained by

taking it equil to the dissociative recombination coefficient

a. = 1D = 2 x 10 cm sec -1 (1a)D

but not :,maller than

a > 10 8 cm 3 sec- (b)

-7-

If IN7, Io2, IO and INO are the phot>-ionization rate coefficient of NZ,22

02, 0 and NO, respectively, it is possible to write the general ionization

equations for equilibrium conditions. If X is the ratio of negative ions

to electrons, these rel3.ions are

n(N 2 ) INn+(N 2 ) 2 (12)

Yn (0) + y9nr(0 2 ) + (2N + Xai)ne

n(O) [10 + Y8 n+(N 2 )1 (13)n+(O) = (13)___ __ _

-yln(N,) + -y2 n( 02 ) + (Y3 + Y4 )n(NO)

++n(O 2) i0, + Y2 n +(0) + y9n +(N 2) I+ Y4 n +(0) n (NO)

+(0) = (14)2 Y5n(NO) + y6ii(N) + v7n(N2) + (a2 + X ai) ne

+ n(NO)[ INO +. y 3 n+(0) + y 5 n+(0 2 )] + y1 n(N,)n+(0) + [-Y6 n(N) + Y7 n(N 2 )n+(0 2 )}n (NO) =

(aNO + X ael)ne

(15)

3. Nitric Oxide and Atomic Nitrogen

As pointed out earlier, the ionic processes can play a role in the

production of nitrogen atoms and of nitric oxide. There is a production

of nitrogen atoms.

dn(N) n+ + + 2a n+(N ) . (1otit- ra NO n+(NO) n + Y In+(0) n 2 N2 n e

A production of nitric oxide comes from

-8-

dn(NO) 7 n(N 2 ) n+(O 2 ) (17)

These productions of N and NO by ionic reactions must be added

to chemical production [Nicolet, 1964] by

dn(N) = n(NO)JNO + 2n(N2 ) 1N 2 (18)

corresponding to the photodissociation of NO and N., and

dn(NO) - [b 1 n(O) + b7 n(O2 )] n(N) (19)

corresponding to the reactions

(b1 ) ; N + O(+ M) -- NO(+ M) + 150 kcal (20)

(b 7) ; N + 0 2 -- NO + 0 + 32 kcal. (21)

The common loss process

(b6) ; N +NO N 2 +O + 75 kcal (22)

combines with (20) and (21) as

dn(N) - [b nWn) + b6 n(NO) + b7 n(O)] n(N) (23)

and

dn(NOd = n(NO JN + b n(N) n(NO) (24)

Using the ionization equilibrium equations (12) to (15) which can

be applied to the D, E and F 1 layers, plus the chemical reactions, the

following expressions arc obtained for NO and N, neglecting the term

X ai n+(NO)ne

-9

•dtO + n(NO) [J + 'NO + b6 n(N) + (Y3 + Y4 ) n+(O) +Y 5 n+(

n(N) [b 1 n(O) + b 7 n(O 2 )j + Y7 n+(O2) n(N 2 ) (25)

dn(N) 7 * +( * n(.[) b n(O) + 6 n(NO) + b7 O = n(NO) [JNO + IN+ y4) n (0)

+ Y5n+(O2)] + n(N2) [2JN2 + 2y, n+(O) + Y7 n+(0 2 )1 + 2 N2 n+(N 2 ) ne

(26)

The conditions for the simultaneous variation of n(NO) and n(N) can

be conveniently written, from (25) and (26),

dn(NO) dn(N)d . + -C- + 2b 6 n(NO) n(N)

2n(N2[JN + Y7 n+(0 2 ) + y1 n+(0)] + 2a n (N 2) ne (27)

For equilibrium conditions, (27) leads to

b 6 n(NO) n(N) = n(N 2 ) [JN2 + Y7 n+(0 2 ) + yI n+(O)] + tN2 n +(N2) ne (28)

or

n(N) [b 1 n(O) + b 7 n(O 2 )= n(N 2 ) JN2 + y1 n (0)] +2

+ n(NO) [JNO + INO + (Y3 + Y4 ) n+ (0) + Y5 n+(O2)] (2-9)

The effect of ionic reactions on N and NO concentrations is easily

und,-rstood since the terms with the symbol gamma correspond to the

ionospheric production of atomic nitrogen or nitric oxide.

-1 0-

4. Ionospheric Conditions in Various Ionospheric Layers

Equations (12) to (15) lead to the general ionization for steady

state conditions

n(N2 11N 2+ n(O) 10 + n(O 2 ) 10 + n(NO) I NOn2 N2 I2 N

n{n+(N2 )[ N + Xai ] +n+(09[a0 + X& +n+(NO)[ NO +k>aii} (30)n N2 aO2 ia

All loss processes of electrons occur by molecular recombination

through ionic reactions.

The essential characteristics of the loss processes for N+ ions2

is the competition between charge transfer and dissociative recombination.

The absence of N ions in the E layer is due to the effect of charge2

transfer. Assuming that the N2+ loss in the D region by dissociative

recombination ib inappreciable compared with other processes, (12)

becomes

n+ + (+9 n(0)] = X n(N2 ) N (31)) Y8 2 2

where X = 1. The parameter 0 < X < 1 reaches its minimum value

in the F 2 layer; it can be taken as unity in the D and E layers and is still

about I in the F 1 layer. This leads to a simplification of (30) for the

lower ionospheric layers where we are considering the behavior of

production of NO and NO+. (30) can be conveniently written as follows:

X. n(N2) IN2 + n(O) Io + n(0 2 ) 102 + n(NO) INO =

ne {n+(O,) [ ao + kai + n+(NO) [aNO + x a (32)ne n(Oz)[ •2

where X = 1.

It is natural to compare (32) with the ionization equation (15)

related to NO+:

ne n+(NO) [aNO + Xa] n+(O2) [Y 6 n(N) + -Y7n(N2)] + n+(O) y1 n(N 2 )

n(NO) [INO + Y3 n+ (0) + Y5 n+(OQ)] (33)

At sufficiently high altitudes the first term ou the right of (33)

certainly becomes negligible and the presence of NO + ions depends on the

direct photoionization and especially on the reactions involving the

atomic oxygen ion. An attempt at determining the concentration of NO+

in the F region must be made on the basis of such an interpretation. In

the E layer, where atomic oxygen ions do not play an important role+ +

and where the NO concentration is comparable to that of 02 , the reaction

between Oý and N2 cannot be considered as a negligible process. The

direct photoionization of NO by Lyman-a is certainly the essential NO

ionization process in the D region, particularly during quiet solar

conditions when the X-ray ionization is inappreciable. However, the

penetration of Lyman-a into the lower D region is limited by molecular

oxygen, and the ionization produced there is due to cosmic rays. Under

such conditions, (33) becomes

ne n+ (NO) [aNO + k a.] = n+(O 2 ) [Y 5 n(NO) + Y6 n(N) + Y7 n(N 2 )] (34)

and since atomic nitrogen does not exist in sufficient quantity,

nn +(NO) Y7 n(N 2 ) + Y5 n(NO)

n+( 2) aNO + X ai

-12-

which is the proper ionization equation to apply below the region where

Lyman-a ionizes NO.

Taking aNO + xai = XO2 ka. in the general equation (32) and

representing the production processes by q, we write:

q (+ ) (aD+Xai) n . (36)

Introducing (.6, in (35), the following ratio is obtained

+n (NO) = y7 n(N2 ) + Y5n(NO)

n (0 2) [(aD + Xai)q/(l +X) X)

if NO+ is the principal ion.

At 60 kmn, where only ionization by cosmic rays occurs during

the normal daytime and night-time conditions, n+ (NO) >> n +O2 2),ad

(36) is equivalent to

q = (a D + Kai) n+(NO)ne = [a.• + aD/X][n+(NO)j2 (38)

-2 .- 3 -1With a cosmic ray production of not less than 5 x 10 ions cm sec ,

the time to reach equilibrium conditions is always less than one hour.

Exact ionospheric conditions cannot presently be determined-16 * 1

since the rate coefficient Y7 is not known. A value Y7 = 10 may

be adopted if 0+ has to be eliminated in the lower D region. This2

process has not been observed in the laboratory due to its low absolute

value and it is difficult to determine how it varies with temperature.

Nevertheless, it seems that it is the process which can make the

observational results of Narcisi and Bailey [19641 understandable. The

absence of 0+ at 65 km with a ratio l(NO+ )/n+ (O) greater than 50 below2

75 km and a rapid decrease to less than 5 near the mesopause require

- 13 -

processes other than that due to dissociative recombination, It is

difficult to see how the X ray production, as compared with the Lyman-a

intensity, could favor such a vertical ionic distribution.

In the E layer, it could be claimed, however, that the process

between 02 and N is negligible and, hence, that it is not responsible

for th,-, presence of NO+. Nevertheless, such a conclusion is premature.

Thus, finding in observational data [Holmes, et al., 19641 that

n +(NO) = n+ (02) in the daytime E layer, equation (33) at 100 km

leads to

ne n +(NO) aNo = 10 5 x 5 x 10 4 x2x1- 7 =00c- 3 sc-1nn~NOaN =l0 xx ~x 2x I0 = 1000 cm sec

(39)

As a result, we are led to consider that a process like 0+ + N2 --. NO + + N

or n(NO) INO is, in fact, important. If n(NO) is 108 cm"3 or less, the

-3 -1direct photoionization is then less than 50 cm sec The best

attempt at determining a production of more than 100 NO+ ions cm -3sec l

at 100 km would be to consider a very small concentration of 0+ ions.

The X-ray production would always be the essential process

To obtain information on the existence of the reaction process

0+ 4 N --- NO + +O, it is perhaps necessary to consider night-time2 2

conditions in the E layer In view of the observational results obtained

for the night-time E layer (Holmes et al. , 1964]. we may put forward

the hypothesis that the ratio n (NO) > n+ (0) depends on the ion-

interchange process, i. e.

nyn(NO)yn(N,) + y n e0 -1 (40)•/Sn(O)+ Y7 i- + O e - sc(0

13 12 - a -16 -15 3 -IWith n(N 2 )_ 10 to !0 cm and 10--l to 10 cm sec

- 14 -

considera.tion must be given to the process involving 0+ and N However,2 2'

it is scarcely worth pursuing this at the present time since rocket and

laboratory experiments are not yet sufficiently developed. The

uncertainties are necessarily very great since the rate coefficients are

not as yet determined and since the observational results are inadequate.

It would be unwise to abandon either of the processes under discussion

yln+ (0) or (y5 + y7 ) n+ (0,.) because of lack of accord with cne or another

particular result.

It is worth pointing out that, if the dominant process during day-

time conditions for NO + ions is ion-atom interchange with atomic oxygen

ions, the problem of explaining the whole situation becomes almost-7 3 -1

impossible. For example, assuming aNO = 0O2 = 2 x 10 cm sec32

and 105 electrons cm- at 100 kin, equation (32) leads to

a2ne = q = 2000 electrons cm sec-1 (41)

which is an acceptable value for the electronic production at this height

level. On the other hand, (33) can be conveniently written as follows

an+(O2 )ne q - y1 n(N 2 ) n+ (0) (42a)

and

on +(NO) n yl n÷(N,) n + (0) . (42b)

In order to attain a ratio n+ (NO)/n+(O2 ) + ( , it would be

necessary to assume that the electron production by atomic oxygen is at

least 50 percent of the total production at 100 kmn. Such a requirement

cannot be accepted since the photoionization of 02 and N2 cannot be less

important than that oi atomic oxygen at 100 km. and below. Obviously,

- 15 -

the recombination coefficient of NO + should be less than that of 0 +2

to relate the production of nitric oxide ions only to the presence of

atomic oxygen ions.

The charge transfer 0 + N + cannot play an important role in2

the production of atomic oxygen ions at relatively low altitudes; the

N + concentration is too low in the lower E layer to be sufficient to2

produce the ionic density which is needed.

At present, it appears that the ion-atom interchange of 0 +2

cannot be excluded and the following equation can be written in the E

layer and D region where negative ions are not important,

a n + (NO)n n + (0 0 n (NO) + n(N + n (NO) (43)NO e 2' [ Y5 'Y7 2)1 'NO

5. Total Production of Nitric Oxide

An attempt to determine the absolute concentrations of nitric

oxide and atomic nitrogen in the D and E regions is difficult since the

ionospheric rate coefficients are not known, However, starting from

(28) and (29), the NO concentration is given by a quadratic equation which

may be conveniently written as follows

b n(O) + b n(00n (NO) I b- 7

n (N [i N + -V I n (0) + _Y7 n (0 2))

n(N ff i + yln + (0)] + n(NO)rJ +1 + (-Y + -Y )n + (0) + -yr n +2 N 2 NO NO 1 4 3 (01))

(44)

- 16 -

If we consider that the production of nitrogen atoms from N2 is

important, we obtain

b n(O) + b 7 n(O 2 ) + Y7 n+(0) (4n(NO) - b6 I+ _ __ 1(45)62 + Yin+(0) J

+ n+O

The limit, with y, n (0) > Y7 (a) corresponding to the

F region, is

*b n(O) + b 7 n(O 2 )n (NO) - ____ (46)

b6

since the ion-atom interchange process in which 0+ is involved increases

rapidly with altitude. n *(NO) corresponds to the photochemical

equilibrium value given by [Nicolet, 1964]

n(NO) b n(O) + b7 n(O 2)-M b 6bn(N) + JNO + INO

with the following requirement

"n(N) > NNO + INO - 2.5 x 104 4 sec-I (48)b6

For example, such conditions can be applied at 150 km in the F 1 layer

where

n(N,) [Y , n+(O) + 1 N (I-X)1

"n(N) :2 (49)1) n* (NO)

which shows that the production of nitrogen atoms is essentially due to

the ion-atom interchange process.

At sufficiently low altitudes, the production of nitrogen atoms

- 17 -

from nitric oxide is important. Thus (44) is written

n 2 (NO) n * (NO) n(N 2 ) DJN 2 + vl n+(O) + y7 n+(O 2 ) (50a)

NO + 'NO + [v 3 + Y41 n+(O) + -5 n+(O 2 )

and

n(N 2 ) 2 N + "I n+(C) + Y7 n + 102

n (NO) n*(NO) (50b)

JNO + INO

which leads to

n(NO) n* (NO) b 6 5 x10 5 * (S1T-- rN nN 05.(NO) 11NO +NO

Thus, the atomic nitrogen concentration would be, for such

conditions, less than that of nitric oxide where n*(NO) > 2 x 104 cmn3

This inequality is, in fact, satisfied everywhere as shown in Fig. 2. If

we consider again the conditions at 100 k-n where

* 6 -3 13jNO + INO 5 x 10-7 -1n(NO) -" 0bcm .n(N2)=101 -m.J +151 sec=

eauation (50b) leads to

n(NO) - 5 x 10 N + v1 n (O) + y7 n+(0 2 )I cm- 3 (12)

Any value of a rate coefficient in the bracket ot (S2) not less14 -I1 * 1NO1

than 4 x 10 sec *eads to n(NO) > n (NO)- 10 cm sec ; that is a

value greater than the photochemical value. If the rate coefficient

Y7 n+ (0,) reaches values between 10"11 and 10- Ic0 the nitric oxideco nra

concentration is between 2 x 10' and 5, x 1'cm sec -

- 18 -

.... I I I I

030

120

110

E100-

SCHEMOSPHERE IONOSPHERE

_j go(1) (2)

so,1- \\\ j\

70h _ _ _ _ _ _ _ _ _ _ _ _

I nP(NO):3x16'n(M) o3xide(M

10 ~ ve 10 1 10 010'CONCENTRATION (cm-3)

Fig. 2. Vertical distribution of nitric oxide. (1) Photoequilibriu-conditions in the chemosphere; (2) photoequilibrium conditionsin the ionosphere; (3) and (4) mixing conditions.

• , .• : ._ .. . . - . . - • r ., , : - . _ • : , . . o • . . . • . . .. . . . ... . . . . .. . .

- 19-

An attempt may be made to determi:ne the vertical distribution of

NO for photoionization equilibrium conditions. Due to the lack of infor-

mation concerning the ratio n +(NO)/n+ (0 2 between 85 km and 110 kin,

we assume that the electronic concentration increases from 2. 5 x 103 cm-3

at 85 km tn 104 cm-3 at 90 km -nd I x 105 at 100 km with a rate coefficient

-16 -1 instead of Y7 n+ sec With such a hypothesis an

approximate form of the vertical distribution can be obtained. Fig. 2

illustrates the effect of the production of NO by the reaction beiiween

0+ and NO. The two curves above 85 km show the vertical distribution02

of nitric oxide, as a function oi chemical reactions and ion-atom interchange

process during daytime conditions.7 -3

The average value of n(NC) is about 10 cm- and, with a thickness13

of about 30 kin, the total content is not less than 5 x G13 molecules-2 14 -2

cm . Since Barth [1964] gives 1. 7 x 1014 cmr above 35 kmn, it is

best at present to regard the proposed solution as the possible

mechanism. However no definite statements are possible in such

aeronomic problems without prior knowledge of •he appropriate

coefficients.

Aa was mentioned above, the mesospheric problenii of nitric

oxide indicates that the density distribution depenL'. on equilibr'arn

conditions near the mesopause. Variations will occur depe ding on

X-ray effects; particularly during high solar activity conditions. No

attempt will be made here to illustrate this since we would then be forced

into adopting all rate coefficients based on laboratory measurements ds

being applicable o- of choosing aeronomic parameters which are as yet

unknown. The curves with n(NO) = 3 x 10-9 n(M) and 3 x 10°8 n(M)

- 20 -

shown in Fig. 2, indicate that a very large change may occur in the

upper mesosphere. The change from chemical equilibrium conditions

to mixing conditions is very marked. Obviously the actual situation

is very complicated since the life-time of NO is not short between 65

and 85 krn. In treating nonequilibrium cases we have to consider

different ionization conditions (intensity and duration) in order to relate

the equilibrium concentrations to the rate of production o- NO, NO+ and

0. In any case, the use of recent laboratory measurements for02•

nitric oxide reactions results in values of NO between 10 and 100 times

the value adopted by Nicolet and ýAikin in the mesosphere.

The essential conclusion is that there is a possibility of

explaining by one ionic process the predominance of NO + ions in the

lower D region and an excess of NO in the region of 100 km. It seems

that Barth's observations should be interpreted by con3idering a peak

in the vertical distribution of NO. Normalizing to his value of14 -2

1. 7 x 1014 molecules cm" for the column density of nitric oxide above

85 kin, the values of n(NO) in Fig. 2 should be multiplied by a factor

of only 3 to give the same total content.

6. Nitric Oxide and the Airglow Continuum

Several authors have suggested that

O + NO -" NO2 +Ihv (X > 3750 A) (53ý

contributes to the airglow continuum [Krassovsky, 1951; Bates, 1954;

Nicolet, 1955; Doherty and Jonathan, 1964]. It may correspond to the

continuum emission with a peak around 100 km observed by rocket

- 21 -

[Packer, 1961]. Adopting the absolute value of 6.4 x 10- 1 7cmnsec 1

obtained by Fontijn et al. [19641 with the following division:3. x1-17 3 -1

3.2 x 10 cm sec for X < 7?50 A and X > 7250 A, [Nicolet, 19641,

it is possible to make a comparisoi- with the observed value of the

airglow continuum. An approximate value of about 6 x 10 9 photons-2 -l

cm sec is given [Krassovsky et al. , 1962] for the spectral range

k k 4000 - 7000 A.

With the NO vertical distribution shown in Fig. 2 and approximate

concentrations of atomic oxygen ior night-time conditions, it is possible

to determine the general emission of the continuum. The result is

illustrated in Fig. 3 which gives the number of photons cm 3sec"I

between 75 km and 115 km. The total emission corresponds to9 - -I 09 -2 -I

3,4 x 109 photons cm sec or 1. 7 x 10 photons cm" sec for the

4000 - 7250 A range. Normalizing to the observed value, the

theoretical flu,- should be multiplied by a factor of about 3 to give the-2 -1

same number of photons cm sec This is the same factor which was

used to obtain the total number of NO molecules observed by Barth

[1964]. This may be pure coincidence. Nevertheless it corresponds

to an average value of 3 x 10-16 cm 3sec"I for the rate coefficient of the

reaction O + N2 -" NO + NO+ in the region of 100 km, If a steric

factor of the order of unity is assumed for this reaction, an activation

energy of about 6 kcal should be expected, i. e.

= -11 1 -6000/RT 3 -17.5 x 10"I T e cm sec (54)

ALTITUDE (kin)

---5 -

z S.

0

4'W .4

o z-o0 0

- 0!

-

67•

a

"- ?z -

- 23 -

7. Conclusions

An attempt has been made to deterrrine the ionic formation of the

D region by adopting an origin [Nicolet ard Aikin, 1960] due to the

simultaneous effects of cosmic rays in 'he lover D region with the

photoionization of nitric oxide by Lyman-a plus a variable contribution

from X-rays of X < 10 A fo: the main part of the D-region which is

below the mesopause level (near 85 kin). The charge transfer process

+transforming N into 0 + leads to a general deduction about processes2 2

involving 0+ ions and the determination of the ratio n+ (NO)/n+(O2 ).

By studying the vertical distriotaion of this ratio it has been shown that

all the 0+, and N + ions prod ced by cosmic rays in the lower D region2 2

(altitude < 70 km) art+ transformed into nitric oxide ions, i. e.

equation (38),

qc(N+, 0, (aD + Xai)n+(NO)ne = [a + •D/X][n+(NO)]2

(55)

In the main D region, there must be an increase of the ratio

n+(0 2 )/n+(NO) with height which is limited by the direct photoionization

of nitric oxide. Equations (32) and (33) can be simplified as

aNn +(NO)ne n(NO) INO + n +(O[0 n(NO) + \'7 n(0 2 )]

(56)

and

aNOn+(NO)ne + co2n+(O2)ne = n(N2) IN2 + n(O)I 0 + n(O 2 )10 2 +n(NO)I2 2n2 NO)

(57)

These two equations suggest that any disturbance due to an

- 24 -

increase of solar X-ray emission affects the ratio n+(O92/n+(NO) in a

complicated way since it always involves an increase of ionic reactions

containing molecular oxygen ions. A corresponding increase of NO

should be observed, particularly near the mesopause.

In the E layer, (57) remains a satisfactory expression for the

total ionization. However, the subsidiary effect of atomic oxygen ions

cannot be neglected, particularly in the upper part of the E layer, and

instead of (56), the more general equation (33) must be used,

ain + (NO)ne = n(NO)INo + n+(O 2 )[ Y5 n(NO) + Y7 nlN 2 )] + r+(O) [Ivn(N2 )-L Y3 n(NO;J

(58)

This ionization equation along with the general equation (44) giving

n(NO) shows that there must be an ion-atom interchange process between

0 +and N . The existence of such a reaction implies a substantial

increase of nitric oxide in the E layer compared with its photochemical

value. This idea has been elaborated upon in order to explain how,14 -2

above 85 kin, a total content of the order of 10 NO molecules cm

[Barth, 1964] and an emission of the order of 109 photons cm 2sec'l

[Krassovsky et al., 1962] in the continuum (X > 4000 A) of the night

airglow are related to ionospheric processes in the E layer.

- 25 -

REFERENCES

AIKIN, A.C., J.A. KANE and J. TROiM, Some results of rocketexperiments in the quiet D region, J. Geophys. Res., 69, 1964.

BARTH, C.A., Rocket measurement of the nitric oxide dayglow,J. Geophys. Res., 69, 3301, 1964.

BATES, D.R., The physics of the upper atmosphere, Chapter 1Zin The Earth as a Planet, Ed. G.P. Kuiper, Univ. Chicago Press,Chicago, 1954.

BELROSE, J.S., Present knowledge of the lowest ionosphere, p. 3in Propagation of radio waves at frequencies below 300 kc/s,Pergamon Press, Oxford, 1964.

BIONDI, M.A., Electron-ion and ion-ion recombination, AnnalesG~ophys., 20, 5, 1964.

BOURDEAU, R.E., Ionospheric research from space vehicle,Space Science Rev., 1, 683, 1962.

BRANSCOMB, L.M., A review of photodetachment and relatednegative ion processes relevant to aeronomy, Annales Giophys.,20, 88, 1964.

DOHERTY, G., and N. JONATHAN, Laboratory studies of thechemiluminescence from the reaction of atomic oxygen withnitric oxide under atmosphere conditions, Disc. Faraday Soc.,35, 1964 (to be published).

FARRAGHER, A.L., F.M. PAGE and R.C. WHEELER, Electronaffinities of the oxides of nitrogen, Discus.. Faraday Soc. , 37, 1964.

FONTLIN, A., C.B. MEYER, and H.1. SCHIFF, Absolute quantumyield measurements of the NO-O reactions and its use as a standardfor chemiluminescent reactions, J. Chem. Phyrs., 40, 64, 1964.

FRIEDMAN, H., Ultraviolet and X-rays from the sun, Annual Rev.Astronomy and Astrophysics, 1, 59, 1963.

HOLMES, J.C., C.Y. JOHNSON and J.M. YOUNG, Ionospheri,.chemistry COSPAR meeting, Florence, May 1964. to be published.

KRASSOVSKY, V.I., Influence of water vapor and carbon monoxideand nitric oxide on the luminescence of the night sky, Dokl. Akad.Nauk., S.S.S.R., 78, 669, 1951.

KRASSOVSKY, V.I., N.N. SHEFOV, and V.I. YARIN, Atlas of theairflow spectrum, Planet, Space Sci., 9, 883, 1962.

- 26 -

NARCISSI, R. S. and A. D. BAILEY, Mass spectrometric measurementsof positive ions at altitudes from 64 to I 12 kilometers, COSPARmeeting, Florence, May 1964, to be published.

NICOLET, M., Nitrogen oxides and the airglow, J. Atm. Terr. Phys.,7, 297, 1955.

NICOLET, M., Nitrogen oxides in the chemosphere, J. Geophys. Ret;.,(in pr'ess).

NICOLET, M. , and A.C. AIKIN, The formation of the D region of theionosphere, J. Geophys. Res., 65, 1469, 1960.

NICOLET, M., atd W. SWIDER, Jr., Ionospheric conditions, Planet.Space Sci., 11, 1459, 1963.

PACKER, D.M., Altitudes of the rght airflow radiations, AnnalesGeophys., 17, 67, 1961; IAGA Symposium 1, 145, 1961.

REID, G.C., Physical processes in the D region of the ionosphere,Rev. Geophys., 2, 311, 1964.

SAGALYN, R.C., and M. SMIDDY, Rocket investigation of theelectrical structure of the lower ionosphere, Space Research IV, p.371, North-Holland Publ. Cy, Amsterdam, 1964.

WHITTEN, R.C., and I.G. POPPOFF, Ion kinetics in the lowerionosphere, J. Atm. Sc., 21, 117, 1964.

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V REPORT TflLE

ION03PHIERIC PROCESSES AND NITrRIC OXIDE

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Scientific Report No. 228S. AUTNOOVS) (Last maw, first Puv', LRiUO)

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13. ABSTRACT

Analysis of ionic processes in the ionosphere leads to theconclusion that nitric oxide andl its ion are produced by a reactionbetween nitrogen molecules and molecular oxygen ions. Stich aprocess implies a substantial increase of nitric oxide in theE layer to a value greater than the photochemical concentration.In the lower D region, N~ and 0+t ions produced by cosmic rays1 2are transformed into NO+ ions. A quantitative estimatte showsthat these conclusions are consistent with observationatl diata inthe chemosphere and ionosphere and also suggests theexplanation of the night airgiow continuum.

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ionospheric processes and nitricoxide

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