Infrared processes in the Jovian auroral zone

ICARUS 7~, 399-408 (1988)

Infrared Processes in the Jovian Auroral Zone SANG J. KIM Code 633, National Space Science Data Center, Goddard Space Flight Center~NASA, Greenbelt, Maryland 20771 Received J a n u a r y 12, 1987; revised D e c e m b e r 7, 1987

A theoretical model of vibrational excitation and deexcitation processes of CH4 and H2 on the Jovian auroral zone is presented. The emission intensities of the v3 and v4 bands of CH4 are calculated assuming electrons as bombarding particles, and compared with Voyager 1 IRIS observations. It is shown that the thermal emission of the CH4 band dominates over the nonthermal emission that is directly or indirectly caused by particle bombardments. © 1988 Academic Press, Inc.

INTRODUCTION

Strong 10-t*m infrared emission of hydrocarbons on the Jovian auroral zone has been observed from the ground (Caldwell et al. 1980, 1982) and from Voyager 1 IRIS (Infrared Interferometer Spectrometer) (Kim e t al. 1985). This infrared auroral activity is the most energetic phenomenon (>10 ergs/sec cm 2) compared with other auroral activities: extreme ultraviolet aurora ( - 1 0 ergs/sec cm 2) (Broadfoot et al. 1979, Yung et al. 1982), and X-ray aurora ( - 1 0 -4 ergs/sec cm 2) (Metzger et al. 1983). There were attempts to understand the 10-/~m auroras in terms of electron precipitation and to predict intensities of 2-/~m H2 quadrupole lines and 3 - / ~ m C H 4 bands using theoretical particle precipitation models (Kim and Maguire 1985, Kim 1985). Recently Trafton et al. (1987) reported an apparent detection of the $1(1) line of H2, a quadrupole line at 2.12 ~m. Although they missed the auroral hot spot at hni(1965) = 180°, they could find -6o- emission of the Sl(1) line at hni (1965) = 220 ° that is about 14% of the predicted value of Kim and Maguire. There are several unanswered scientific questions about these auroral phenomena: (1) What kind of magnetospheric parti-

cles are responsible for these auroras? Several possible energy sources have been speculated about, including electrons (Yung et al. 1982), protons (Goertz 1980), and oxygen and sulfur ions (Metzger et al. 1983, Gehrels and Stone 1983). Ions have been the favored theory for the energy source during the last few years. However, electrons have never been unambiguously ruled out as the candidate (Herbert et al. 1985). (2) Are the particles causing the IR aurora or indirect energy transfer from H2 processes at higher altitudes also responsible for the UV and X-ray auroras? Yung et al. (1982), analyzing IUE data, estimated the electron energy spectrum to be in the range of 1-30 keV. However, these electrons may not produce the 10-~m thermal IR emission of hydrocarbons because these energetic electrons cannot reach the major hydrocarbon layers in the stratosphere of Jupiter. For example, 30-keV electrons can reach about 2-/~bar level where the number densities of hydrocarbons decrease exponetially (see Fig. 18 of Broadfoot et al. 1981). (3) An observation requiring explanation is the discovery of CzH4, C3H4, and possibly C6H6 in the Voyager 1 IR spectra of Jupiter's north polar region (Kim et al.

399 0019-1035/88 $3.00 Copyright © 1988by AcademicPress, Inc. All rights of reproduction in any form reserved.

400

SANG J. KIM

1985). To date, there is no convincing energetic particle chemistry for the enhancement of these molecular abundances.

1981). Completion of the theoretical model, including all the minor molecules, is deferred to future works. In order to calculate the number of vibraThis paper is one contribution to solving tional-rotational excitation states of CH4 these outstanding questions. A theoretical and H2, a nonrelativistic electron energy model for vibrational excitation and deexdeposition program originally developed by citation processes of CH4 and H2 is dePeterson et al. (1973) was modified. This scribed assuming electrons as bombarding program apportions the incoming electron particles. The emission intensities of the u3 energy in various excitations, ionizations, and v4 bands of CH4 are calculated and and dissociations of CH4, H2, H, and He. compared with the Voyager 1 IRIS obserRelative populations for all states are comvation. The consequence of proton or ion puted following the complete energy degprecipitation on the auroral zone will be radation of the primary electron, and all discussed in future works. generations of secondaries form during OBSERVATIONS ionization events. In the calculation, a continuous-slowing-down approximation was Voyager 1 IRIS data were used to obtain used for the energy of incident auroral the excessive flux of the u4 band of CH4 in electrons. An updated cross-section compithe north polar IR auroral zone. Selection lation for electronic transitions, dissoof the hot spot data was described elseciative excitations, dissociative ionizations, where in detail (Kim et al. 1985). Figures 1-3 of Kim et al. were utilized to estimate vibrationsl and rotational excitations of the amount of the excessive CH4 u4 flux CH4 and H2 (Tables I-A and I-B), and over the north polar auroral zone. The IR excitations and ionizations of H and He hot spot covers the area of about 2.2 x 108 was prepared for the input parameters in km 2 (Caldwell et al. 1987). Within this area the electron deposition program. The detemperatures are not uniform; therefore, tailed description of the analytical paramethe particle precipitation flux and energy ters for the cross sections is presented in range may not be uniform. In this paper, Appendix A. Given these cross sections, the number however, the IRIS spectra were averaged densities of CH4 and Ha in certain excited over the hot area, and an average effect on states can be calculated when all the precipthe auroral zone was considered. The esitating electrons are degraded locally. For timated averaged excessive flux of the u4 the application of this program to auroral band of CH4 is 9.6 --+ 0.5 ergs/cm 2 sec sr, electron precipitation in a hydrostatic atwhich is about the same as the result of mosphere, Eq. (3) of Heaps et al. (1973) Caldwell et al. (1980). was employed. Then the volume excitaTHEORETICAL CALCULATIONS tions rate of the certain states of CH4 and AND RESULTS H2 at certain altitudes was estimated by Only four major constituents are in- adopting Eq. (4) of Heaps et al. For an upper atmosphere temperature cluded in the model, H2, H, He, and CH4, assuming that the effects of other minor structure (2.0 x 10 -3 to 1.0/~bar), an equahydrocarbons on the radiative transfer pro- torial result from stellar occultation data in cesses are negligible. C2H2 has been ex- Fig. 18 of Broadfoot et al. (1981) was cluded from the model because at the l- adopted since no realistic auroral temperambar level its mixing ratio is about 3 x 10-8 ture profile is available now, and the model compared to 2 × 10-3 for CH4, and at 10 in this paper is not very sensitive to the p~bar the C2H2 mixing ratio is about 10 times temperature profile in this pressure range. less than that of CH4 (Broadfoot et al. For the middle stratosphere (10-100/xbar),

JOVIAN INFRARED

401

AURORAS

T A B L E I-A H2

W

W

f~

J = 0-2 1-3 2-4 3-5 4-6 5-7

0.044 0.074 0.102 0.131 0.158 0.183

0.476 0.476 0,476 0,476 0.476 0.476

Rotational states 0.6 0.6 0.6 0.6 0.6 0.6

v = 0-1 0-2 0-3

0.53 1.06 1.59

1.20 1.40 1,40

Vibrational states 2.0 2.0 2.0

F

B IE,(Lyman) C 117,,(Werner)

13.013 12.465

Electronic excited states C 13.013 0.325 12.465 0.300

a 3~h 3X~3Eft(4so') b 3~+ f 3~(1) f 3E~+(2) c 317. d 311, k 3II, g 3~p 3~g+ i 317g r 31Ig j sag s 3Ag v 311e

11.890 13.980 14.500 10.000 13.360 14.470 11.870 13.970 14.680 13.980 14.690 14.010 14.700 14.030 14.690 14.670

11.890 13.980 14.500 10.000 13.360 14.470 11.870 13.970 14.680 13.980 14.690 14.010 14.700 14.030 14.690 14.670

Lyman series Werner series

H{

/i

/3

v

16.00 16.00

0.85 0.85

1.464 1.464

1i

K

KB

16.00

2.07

0.0

fl

v

0.000394 0.001430 0.000226 0.000193 0.000010 0.000003

0.95 0.95 0.95 0.95 0.95 0.95

3.0 3.0 3.0 3.0 3.0 3.0

0.032 0.0034 0.000366

1.0 1.0 1.0

3.0 3.0 3.0

0.3107 0.3923

0.850 0.850

1.464 1.464

0.125 0.0005 0.0003 0.5 0.0051 0.0026 O. 16 0.0065 0.0005 0.0007 0.0003 0.0005 0.0013 0.0039 0.0002 0.0047

3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0

1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0 1.0

3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0 3.0

Rydberg states 8 C -0.20 0.08

0.31 0.31

F*

A.F.

n

A.F.

n

A.F.

n

1.77 2.23

0.0 0.0

3 3

0.0 0.0

4 4

0.0 0.0

5 5

Fs

F~

Ts

TA

TB

7.07

-7.7

1.87

1000.

32.0

Ionization states J JB Jc 0.059

a constant temperature (230°K) of Drossart et al. (1985) was used. For the lower stratosphere (>1 mbar), a result obtained by inversion of spectral radiances was used (Kim et al. 1985). To obtain the thermal

0.0

0.0

structures between these pressure ranges, a linear interpolation was used. Figure 1 illustrates the Jovian infrared auroral processes caused by energetic electron precipitation. Possible ohmic dissi-

402

SANG J. KIM T A B L E I-B

W

v2 & v4 vl & v3

Lyrnan a Lyman/3 B a B/3 B 3' B 8 H(2s)-H(ls) CI(1657A) CI(1561A) CI(193 IA) CH

H~ CH~CH~ CH~H÷ CH + C+

W

0.162 0.374

0.006 0.011

Methane fl

F

/3

v

Vibrational states 0.02 0.02

0.176 x 10 7 0.591 x 10 7

1.000 1.000

1.000 1.000

11.89

One representative electronic state 10.00 0.6 0.109

1.000

3.000

21.90 21.90 21.90 21.90 21.90 21.90 15.56 27.58 28.08 28.00 21.82

28.64 28.63 23.53 23.86 24.06 24.38 15.56 41.20 38.14 32.42 31.82

Ionization states 1.40 1.40 1.25 1.275 1.29 1.315 1.40 1.85 1.85 1.85 1.40

1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000 1.000

3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000 3.000

lj

K

15.5 10.0 20.0 14.0 20.0 27.0 24.0

0.013 0.775 0.775 0.177 0.105 0.097 0.045

1.72 0.0592 0.335 0.0875 0.0382 0.0234 1.72 0.0432 0.0191 0.0138 0.731

Dissociative excitation states KB J JB Jc 0.0 0.0 0.0 0.0 0.0 0.0 0.0

1.00 1.00 1.00 1.00 1.00 1.00 1.00

pation--so-called Joule heating--due to currents driven by auroral electric fields was excluded. At the present time, proper models are not available for the Jovian auroral electric field, which can accelerate incident electrons. The most uncertain part of the model calculation is the energy flux spectrum of incident electrons on the auroral zone. Monochromatic electron energies of 5 to 100 keV were used for the demonstration of the model calculation. For total input energy flux, Yung et al. used 10 ergs/sec cm 2. This value may be the lower limit for realistic calculations because the energy required to produce the infrared auroral flux of the 7.8-/zm band of C H 4 alone is

0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0

Fs

FB

7~

TA

TB

20.0 39.5 39.5 10.5 11.3 10.0 6.50

0.0 0.0 0.0 0.0 0.0 0.0 0.0

19.0 16.0 12.5 16.5 19.0 19.0 19.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0

0.0 0.0 0.0 0.0 0.0 0.0 0.0

about 9-10 ergs/sec cm 2. Therefore, total incident electron fluxes of 10-100 ergs/sec cm 2 were used for the model calculation. For the c a 4 mixing ratio distribution, a result from a stellar occultation performed by the Voyager 2 Ultraviolet Experiment (Festou et al. 1981) for the high stratosphere (270-3430 km) and a result from an analysis of Voyager 1 IRIS spectra (Gautier et al. 1982) for the low stratosphere (80-150 km) were adopted. Obtaining the CH4 mixing ratio in the 150- to 270-km-altitude range, a linear interpolation of the above results was used. For the H distribution, a result in Fig. 12 of Waite et al. (1983) was adopted. Figure 2 shows results of the number

JOVIAN INFRARED AURORAS

2 MICRON H2 QUADRUPOLE EMISSION

UV AURORA

INCIDENT AURORAL ELECTRON

403

< XCTEH i2 v-v

10 MICRON THERMAL RADIATION

THERMALIZED ATMOSPHERE

[

EXCITED CH4* v -v: NONTHERMAL EMISSION

v-t:

VIBRATIONAL-VIBRA~ONAL ENERGYEXCHANGE VIBRA~ONAL-TRANSLATIONAL ENERGYEXCHANGE

FI6. 1. Excitation and deexcitation processes of H2 and CH4 on the Jovian auroral zone.

densities of CH4 (~'4), CH4 (u3), and H2(v = 1) as a function of altitude after an auroral electron precipitation. H e r e only H2(v = 1) was considered as an important vibrational energy reservoir for the infrared process excluding high vibrational states of H2. The reason for this simplification is as follows: (1) the n u m b e r o f Hz(v = 2, 3, 4 . . . . ) is at 600

I

I

least an order of magnitude less than that of H2(o = 1). This is consistent with a result shown by C r a v e n s (1984); (2) there are no near resonant vibration-vibrational energy exchanges between H2(v = 2, 3, 4 . . . . ) and important CH4 bands; (3) H2(v > 4) plays an important role in chemistry rather than the infrared process. Equilibrium

I

[

I H (v = 1) 2

500 -A

400

i

300

Iv3)

_. . . . . . . . . . . . .

144 (I/4)

__

--

100 ke

200

,**

I

I

I

I

[

-5 10

-4 10

-3 10

-2 10

-1 10

N

FIG. 2. Number densities of H 2 ( o = precipitation.

3

(Excited 8tates/cm sec)

1) and CH4(/.' 3 and ~4) resulting from 100-keV electron

404

SANG J. KIM TABLE

H2(v H2(o H2(u H2(v

= = = =

+ + + +

1) 1) 1) 1)

II

V i b r a t i o n a l r e l a x a t i o n c o e f f i c i e n t ( c m 3 s e c i) at 3 0 0 ° K H2 -- 1 × 10 -16 ( R a m a s w a m y a n d R a b i t z 1977) He -- 1 x 10 -18 ( A l e x a n d e r 1977) H -- 3 × 10 -13 ( H e i d n e r a n d K a s p e r 1972) CH4 -- 3 × 10 -13 (SSH)

CH4(v4) CH4(v4)

+ H2 + He

- - 3.11 - - 1.62

× 10 -~s × 10 -I4

( Y a r d l e y et al. 1973) ( Y a r d l e y et al. 1973)

CH4(/'4)

CH4(/'4)

+ H + CH4

- - 1.59 -- 2.55

× 10 -~z × 10 -t4

(SSH) ( P e r r i n 1982)

CH4(/'3) CH4(/'3) CH4(/'3) CH4(/'3)

+ + + +

-- 2.6 -- 2.18 - - 1.07 - - 7.3

x × × ×

( H e s s a n d M o o r e 1976) ( H e s s a n d M o o r e 1976) (SSH) ( H e s s a n d M o o r e 1976)

H2 He H CH4

Vibrational-vibrational

10 -12 10 -~2 10 -E° 10 -t2

e n e r g y t r a n s f e r c o e f f i c i e n t ( c m 3 s e c ~) at 3 0 0 ° K

Hz(v = 1) + C H 4 - - HE + CH4(vl + v4) - - 4.8 × 10 -13 ( S S H ) ------

cn4(vl CH4(v3 CH4(u2 CH4(v3

H2 H2 H2 H2 H2

+ + + +

v4)

+ cn4 + CH4 /'3) + C H 4 2v4) + C H 4

CH4(/'3) CH4(2/'4) CH4(3/'4)

+ CH4 + ca4 + CH4

/'4)

+ + + + +

CH4(v3 + l)4) - - 4.8 × CH4(v2 + v3) - - 4.8 × CH4(v3 + 2v4) - - 4.8 x CH4(P3) - - 1.3 × CH4(v4) -- 6.0 × CH4 CH4 CH4 CH4 CH4

+ + + + +

Cng(p4) CH4(/'3) CH4(2v4) CH4(2/'3) CH4(3/'4)

------

10 I3 ( S S H ) 10 -13 ( S S H ) 10 -13 ( S S H ) 10 -I3 ( a S H ) 10 i5 ( S S H ) 9.46 4.65 1.58 5.79 2

x × × × ×

10 12 ( H e s s 10 -11 ( H e s s 10 -11 ( H e s s 10 " ( H e s s 10 11 ( H e s s

1980) 1980 + S S H ) 1980) 1980) 1980 + S S H )

C H 4 + CH4(2/'4) - - 1.58 × 10 11 ( H e s s 1980) ca4 + CH4(v4) - - 1.58 × 10 12 ( H e s s 1980) C H 4 + CH4(2/'4) - - 2 x 10 -H ( H e s s 1980 + S S H )

Note. H e r e S S H i n d i c a t e s r e s u l t s u s i n g E q . (A7) o r (A9) o f S S H .

n u m b e r densities of the vibrationally excited states are determined where the vibrational excitation rate is equal to the deexcitation rate. The intensity of a line emission is given by

hv Aji dz e r g s / c m 2 sec sr. I = 4-~ N (Aji + n .o)

(1)

H e r e h is the Planck constant, v is the frequency of a line, N is the n u m b e r of excited states per cm 3 per sec, A j i is the Einstein coefficient, n is the total n u m b e r density, ~ is the total vibrational relaxation coefficient in cm 3 s e c - 1 (for example, for H2 quadrupole lines: H 2 - H , H2-CH4, H 2 - H e , and H2-H2 collisions; for CH4 v3 and v4: CH4-H2, C H 4 - H e , C H 4 - H , and CH4-CH4

collisions), and z is the altitude. The vibrational energy transition rates between constituents are described in detail in Appendix B and s u m m a r i z e d in Table II. As shown in Fig. 12 of Waite et al. (1983), at the 200-km level, CH4 is a major constituent in addition to H2 and He. At 300- to 400-km levels, H b e c o m e s an abundant constituent c o m p a r e d to CH4 and other minor species. Thus, in the 300- to 400-km-altitude ranges, the vibrational relaxation of H2(v = 1) is mostly controlled by H. The CH4 mole fraction is three orders of magnitude less than the H2 mole fraction below 300 km altitude. Since the vibrational relaxation rate of H2(v = 1) by H2 itself is three orders of magnitude less than that of Hz(v = 1) by CH4, two relaxation mechanisms are c o m p a r a b l e in this altitude range.

JOVIAN INFRARED T A B L E III Calculated 2-/xm quadrupole line intensities (5-keV electron, total energy flux = 100 ergs/sec cm 2) Line position (cm i) Sl(0) $1(1) $I(2) Ql(1) QI(2) Ql(3)

4497.84 4712.91 4917.01 4155.26 4143.47 4125.87

Intensity (ergs/sec cm 2 sr) 5.9 1.3 1.9 2.5 6.4 1.2

x × × × x ×

10 -3 10 2 10-3 10 -2 10 3 10 ~

Calculated intensities of CH4 v3 lines (ergs/sec cm 2 sr) Line

Position (cm ~)

Electron energy (keV)

Total energy flux (ergs/sec cm 2) 10

R(0)

3028.7

R(1)

3038.5

R(2)

3048.2

30 100 30 100 30 100

0.0 1.7 × 10 6 0.0 1.6 × 10-6 0.0 3.4 x 10-6

1), or other constituents. The calculated intensities listed in Tables III and IV are nonthermal emissions. The nonthermal intensity of the CH4 v4 band is 10-2-10 -5 ergs/sec cm 2 sr, whereas the observed total intensity of the same band by Voyager 1 IRIS is 9.6 -+ 0.5 ergs/cm 2 sec sr. It is apparent, therefore, that the thermal emission in the methane band dominates over the nonthermal emission. This is consistent with the same conclusion derived from a simple argument of Kim et al. (1985) (see the lower portion of p. 236 and the upper portion of p. 237 of Kim et al.). This result indicates that the thermalization or collision process is a dominant process on the auroral zone in spite of intense particle precipitation.

100 0.0 1.7 × 10 -5 0.0 1.6 x 10-5 0.0 3.4 x 10 -5

In Eq. (1) it is assumed that the lines are optically thin. The Einstein coefficients of the 2-/zm quadrupole lines of H2 and the 1"3 and v4 bands of CH4 were adopted from Turner et al. (1977) and Pugh and Rao (1976), respectively. Theoretical results of the 2-/zm lines of H2 and R(0), R(1), and R(2) lines of the u3 band of CH4 were reported elsewhere (Kim and Maguire 1985, Kim 1985) and are summarized in Table III. In Table IV, theoretical results of the c n 4 /)4 intensity are presented for 30- to 100-keV monochromatic electron energies and for 10 to 100 ergs/sec cm z total energy fluxes. The theoretical intensity of the CH4 b' 4 band can be grouped into two categories: thermal emission, or emission resulting from thermalized velocity (Maxwellian) distribution of CH4, and nonthermal emission, emission resulting from direct or indirect excitation of CH4 by electron, H2(v =

405

AURORAS

APPENDIX A

For the representation of the electronic impact cross sections of discrete states, two different analytical formulae were used. Equations (1) and (2) of Jackman et al. (1977) were adopted for forbidden discrete states and allowed discrete states, respectively. All the notations used in this paper are the same as those of Jackman et al. with the exception of/3 and v which correspond to their o~ and/3, respectively. The above formulae for discrete states were used for vibrational, rotational, and electronic states of CH4 and H2, and electronic states of H and He. For continuum states, Eq. (14) of Peterson et al. (1973) was used. The same notations as those of Peterson et al. were used. This analytical form for continuum states was used for dissociative T A B L E IV CALCULATED INTENSITIES OF THE v4 BAND OF c n 4 (ergs/sec crn 2 sr) Electron energy (keV)

Total energy flux (ergs/sec cm 2) 10

30 100

0.0 1.8 x 10 4

lO0 0.0 1.8 × 10-3

406

SANG J. KIM

excitations and dissociative ionizations of CH4 and H2, and ionizations of H and He. The Hz cross-section compilation in Table I, with the exception of vibrational and rotational cross sections, was provided by Dr. Charles Jackman at NASA/GSFC. For parameterizing cross sections of H z ( v = 1, 2, 3), laboratory observations of Ehrhardt et al. (1968) were used. For cross sections of H2(J = 0, 1, 2, 3, 4, 5), laboratory observations of Crr(J = 1 - 3) of Linder and Schmidt (1971) were used. To generate rotational cross sections other than o-r(J = 1 - 3), Eqs. (1), (2), (3), (4), (6), and (7) of Linder and Schmidt were employed. For parameterizing the vibrational states of CH4, laboratory observations of Pollack (1968) and Duncan and Walker (1972) were used. For the electronic excitation of CH4, a laboratory observation of Vuskovic and Trajmar (1983) was employed. Since no discrete features of the electronic states were measured in the ultraviolet spectrum of CH4 and only broad continuous absorption was observed, a representative total cross section was used as the electronic states. For the dissociative ionization cross sections of C H 4 , laboratory measurements of Adamczyk et al. (1966) were utilized. For parameterizing dissociative excitation cross sections of C H 4 , collective information on laboratory observations of Morgan and Mentall (1974), Vroom and de Heer (1969), and Orient and Srivastava (1981) was used. The cross-section parameters for the excitation and ionization states of He were adopted from Jackman et al. (1977). For parameterizing the excitation and ionization states of H, observation results of Fire and Brackman (1958a,b) were used. APPENDIX B

The temperature-dependent vibrational relaxation coefficients of H2(v = 1) by H2 and He were adopted from Ramaswamy and Rabitz (1977) and Alexander (1977), respectively. The vibrational relaxation rate of Hz(v = 1) by H was adopted from an

experiment result of Heidner and Kasper (1972). The vibrational relaxation rate coefficients of H2(o = 1) by CH4 are not available in the literature. Therefore, they were calculated indirectly from the available information on N2(o = 1)-CH4, CH4(v = 1)-H2, and CH4(v = 1)-N2 collisions, using Eq. (A7) of Schwartz et al. (1952) (hereafter SSH) as a scaling formula. This scaling, however, may give an order of magnitude uncertainty. The values for r/(CH4-H2) and "o(CH4-N2) were adopted from Yardley et al. (1970), and for "o[N2(o = 1)-CH4] from Bishop et al. (1974). The obtained value of "o[H2(v = 1 ) - C H 4 ] is 3 × 10 -13 c m 3 s e c -1 a t room temperature, which is three orders of magnitude bigger than ,/[H2(v = 1)-H2]. Here temperature dependency of the rate coefficients follows as in Eq. (A7) of SSH. Vibrational-translational energy exchanges between C H 4 ( P 4 ) and H2 and He are adopted from Yardley et al. (1970); those between C H 4 ( P 4 ) and H are estimated using Eq. (A7) of SSH; and those between CH4(v4) and CH4 are adopted from Perrin (1982). Vibrational-translational energy exchanges between CH4(v3) and H2 and He are adopted from Hess and Moore (1976); those between CH4(v3) and H are estimated using Eq. (A7) of SSH; and those between CH4(v3) and CH4 are adopted from Hess and Moore (1976). Vibrational-vibrational energy exchanges between H2(v = 1) and combination bands (vl + P4, P3 ~- /"4, P2 ~- /~3, P3 ~2v4) and fundamental bands (v3, v4) of CH4 were obtained by widely utilizing Eqs. (A7) and (A9) as scaling formulae. Equation (A9) of SSH was used for the almost resonant energy exchanges between H2(v = 1) and C H o ( u l + v4, u3 + /24,/~2 -~- v3,/~3 -~- 2u4), and Eq. (A7) of SSH for the nonresonant energy exchanges between H 2 ( o = 1) and C H 4 ( v 3 , /~4).

For vibrational-vibrational internal energy exchanges in CH4, results from infrared fluorescence decay experiments of Hess et al. (1980) were adopted. Since vibrational-vibrational internal energy ex-

JOVIAN INFRARED AURORAS change rates of CH4 in H2, H, or He are not available, the above exchange rates in CH4 were used for the Jupiter model calculations. ACKNOWLEDGMENTS Discussions with Drs. William Maguire, Thomas Cravens, Alan Tokunaga, Maria Moore, Andrew Cheng, John Caldwell, and Rangasayi Halthore have been greatly beneficial to this paper. The original version of the electron energy deposition program (Peterson et al. 1973) was kindly provided by Dr. Charles Jackman of the Goddard Space Flight Center. I thank Karen Satin for her editorial assistance. REFERENCES ADAMCZYK, B., A. J. H. BOERBOOM, B. L. SCHRAM, AND J. KISTEMAKER 1966. Partial ionization cross sections of He, Ne, H2, and CH4 for electrons from 20 to 500 eV. J. Chem. Phys. 44, 4640-4642. ALEXANDER, M. H. 1977. Further studies of 4He-Hg vibrational relaxation. J. Chem. Phys. 66, 46084615. BISHOP, R. H., A. W. SHAW, R. Y. HAN, AND L. R. MEGILL 1974. Infrared processes in the auroral zone. J. Geophys. Res. 79, 1729-1736. BROADFOOT, A. L., M. J. S. BELTON, P. Z. TAKACS, B. R. SANDEL, D. E. SHEMANSKY,J. B. HOLBERG, J. M. AJELLO, S. K. ATREYA, T. M. DONAHUE, H. W. Moos, J. L. BERTAUX, J. E. BLAMONT, D. F. STROBEL, J. C. MCCONNELL, A. DALGARNO, R. GOODY, AND M. B. MCELROY 1979. Extreme ultraviolet observations from Voyager 1 encounter with Jupiter. Science 204, 979-982. BROADFOOT, A. L., B. R. SANDEL, D. E. SHEMANSKY, J. C. McCONNELL, G. R. SMITH, J. R. HOLBERG, S. K. ATREYA, T. M. DONAHUE, D. F. STROBEL, AND J. L. BERTAUX 1981. Overview of the Voyager ultraviolet spectrometry results through Jupiter encounter. J. Geophys. Res. 86, 8259-8284. CALDWELL, J., R. N. HALTHORE,G. S. ORTON,AND J. BERGSRALH 1987. Infrared polar brightenings on Jupiter. IV. Spatial properties of methane, Icarus. In Press. CALDWELL, J., A. T. TOKUNAGA,AND F. C. GILLETT (1980). Possible infrared aurorae on Jupiter. Icarus 41, 667-675. CALDWELL, J., A. Z. TOKUNAGA,AND G. S. ORTON (1982). Further observations of 8/zm polar brightenings of Jupiter. Icarus 53, 133-140. CRAVENS, T. E. 1984. Vibrationally excited molecular hydrogen in the upper atmosphere of Jupiter. Bull. Amer. Astron. Soc. 16, 648. DROSSART, P., E. SERASYN, J. LACY, S. ATREYA, B. BEZARD, AND T. ENCRENAZ 1985. Acetylene, eth-

407

ane and polar infrared brightening on Jupiter. Bull. Amer. Astron. Soc. 17, 708. DUNCAN, C. W., AND I. C. WALKER 1972. Collision cross-sections for low energy electrons in methane. J. Chem. Soc. Faraday Trans. 2 68, 1514-1521. EHRHARDT, H., L. LANGHAMS,F. LINDER, AND H. S. TAYLOR 1968. Resonance scattering of slow electrons from H2 and CO angular distributions. Phys. Rev. 173, 222-230. FESTOU, M. C., S. K. ATREYA, T. M. DONAHUE, B. R. SANDEL, D. E. SHEMANSKY, AND A. L. BROADFOOT, 1981. Composition and thermal profiles of the Jovian upper atmosphere determined by a Voyager 2 ultraviolet stellar occultation experiment. J. Geophys. Res. 86, 5715-5725. FIVE, W. L., AND R. T. BRACKMANN1958a. Collisions of electrons with hydrogen atoms. II. Excitation of Lyman-alpha radiation. Phys. Rev, 112, 1151-1156. FITE, W. L., AND R. T. BRACKMANN1958b. Collisions of electrons with hydrogen atoms. I. Ionization. Phys. Rev. 112, 1141-1150. GAUTIER, D., B. BEZARD, A. MARTEN, J. P. BALUTEAU, N. SCOTT, A. CHEDIN, V, KUNDE, AND R. HANEL 1982. The C/H ratio in Jupiter from the Voyager infrared investigation. Astrophys. J. 257, 901-912. GEHRELS, N., AND E. C. STONE 1983. Energetic oxygen and sulfur ions in the Jovian magnetosphere and their contribution to the auroral excitation. J. Geophys. Res. 88, 5537-5550. GOERTZ, C. K. 1980. Proton aurora on Jupiter's nightside. Geophys. Res. Lett. 7, 365-368. HANEL, R., B. CONRATH, M. FLASAR, V. KUNDE, P. LOWMAN, W. MAGUIRE, J. PEARL, J. PIRRAGLIA, R. SAMUELSON, D. GAUTIER, P. GIERASCH, S. KUMAR, AND C. PONNAMPERUMA 1979. Infrared observations of the Jovian system from Voyager 1. Science 204, 972-976. HEAPS, M. G., J. N. BASS, AND A. E. S. GREEN 1973. Electron excitation of a Jovian aurora. Icarus 20, 297-303. HEIDNER, R. F., AND J. V. V. KASPER 1972. An experimental rate constant for H + H2(v" = l) H + H2(v" = 0). Chem. Phys. Lett. 15, 179-184. HERBERT, F., B. R. SANDEL, AND A. L. BROADFOOT 1985. Observations of the Jovian UV aurora by Voyager. Bull. Amer. Astron. Soc. 17, 711. HESS, P., A. H. KUNG, AND C. B. MOORE 1980. Vibration --* Vibration energy transfer in methane. J. Chem. Phys. 72, 5525-5531. HESS, P., AND C. B. MOORE 1976. Vibrational energy transfer in methane and methane-rare-gas mixtures. J. Chem. Phys. 65, 2339-2344. JACKMAN, C. H., R. H. GARVEY, AND A. E. S. GREEN, 1977. Electron impact on atmosphere gases I. Updated cross sections. J. Geophys. Res. 82, 5081-5090. KIM, S. J. 1985, Three micron emission of CH4 from

408

S A N G J. K I M

the Jovian auroral zone. BullAmer. Astron. Soc. 17, 700. KIM, S. J., J. CALDWELL, A. R. RIVOLO, R. WAGENER, AND G. S. ORTON 1985. Infrared polar brightenings on Jupiter III. Spectrometry from the Voyager 1 IRIS experiment, Icarus 64, 233-248. KIM, S. J., AND W. MAGUIRE 1985. Two Micron Quadrupole Line Emission of H2 from the Jovian Auroral Zone. A paper presented at the Conference on the Jovian Atmosphere, GISS, NY. LINDER, F., AND H. SCHMIDT 1971. Rotational and vibrational excitation of H2 by slow electron impact. Z. Natur. 26a, 1603-1617. METZGER, A. E., D. A. GILMAN, J. L. LUTHEY, K. C. HURLEY, M. W. SCHNOPPER, F. D. SEWARD, AND J. D. SULLIVAN 1983. The detection of X-rays from Jupiter. J. Geophys. Res. 88, 7731-7741. MORGAN, M. D., AND J. E. MENTAEL 1974. VUV dissociative excitation cross sections of H20, NH3, and CH4 by electron impact. J. Chem. Phys. 60, 4734-4739. ORIENT, O. J., AND S. K. SRIVASTAVA 1981. Cross section for Ly-a emission by electron impact on methane. Chem. Phys. 54, 183-188. PERRIN, M. Y. 1982. Photoacoustic study of CH4(v2, v4) deactivation in CH4-CH4 and CH4-monoatomic collisions. Chem. Phys. Lett. 85, 521-527. PETERSON, L. R., T. SAWADA,J. N. BASS, AND A. E. S. GREEN 1973. Electron energy deposition in a gaseous mixture. Comp. Phys. Comm. 5, 239-262. POLLOCK, W. J. 1986. Momentum transfer and vibrational cross-sections in non-polar gases. Trans. Faraday Soc. 64, 2919-2926. PUGH, L. A., AND K. N. RAO 1976. Molecular Spectroscopy: Modern Research (K. N. Rao, Ed.), Vol. lI, pp. 165-227. Academic Press, New York.

RAMASWAMY, R., AND H. RABITZ 1977. Vibrationrotation relaxation in bimolecular collisions with application to parR-hydrogen. J. Chem. Phys. 66, 152-159. SCHWARTZ, R. N., Z. I. SEAWSKY,AND K. F. HERZFEED 1952. Calculation of vibrational relaxation times of gases. J. Chem. Phys. 20, 1591-1599. TRAFTON, L., D. LESTER, J. CARR, AND P. HARVEY 1987. Jupiter's Northern Aurora: Possible Detection of Quadrupole HE Emission. A paper presented at the International Workshop on Time Variable Phenomena in the Jovian System, Flagstaff, AZ. TURNER, J., K. KIRBY-DOCKEN, AND A. DAEGARNO 1977. The quadrupole vibration-rotation transition probabilities of molecular hydrogen. Astrophys. J. 35, 281-292. VROOM, O. A., AND F. J. DE HEER 1969. Production of excited hydrogen atoms by impact of fast electrons on some simple hydrocarbons. J. Chem. Phys. 50, 573-579. VUSKOVlC, L., AND S. TRAJMAR 1983. Electron impact excitation of methane. J. Chem. Phys. 78, 4947-4951. WAITE, J. H., JR., Z. E. CRAVENS, J. KOZYRA, A. F. NAGY, S. K. ATREYA, AND R. H. CHEN 1983. Electron precipitation and related aeromomy of the Jovian thermosphere and ionosphere, J. Geophys. Res. 88, 6143-6163. YARDEEY, J. T., M. N. FERTIG, AND C. B. MOORE 1970. Vibrational deactivation in methane mixtures. J. Chem. Phys. 52, 1450-1453. YUNG, Y. L., G. R. GLADSTONE, K. M. CHANG, J. M. AJEEEO, AND S. K. SRIVASTAVA 1982. Hz fluorescence spectrum from 1200 to 1700 ,~ by electron impact: Laboratory study and application to Jovian aurora. Astrophys. J. 254, L65-L69.