r\bb${ 

//b QY" 

?/ STATE UNIVERSITY OF NEW YORK AT STONY BROOK 

Stony Brook, New York, 11794 

Annual Report for: 

Analysis of EUV Dayglow Speetra of Triton, Titan and Earth 

NAGW- 2483 

Submitted to: 

The Neptune Data Analysis Program 

Dr. William L Quaide (NRA-90-OSSA-10) 

Solar System Exploration Division 

Code EL 

National Aeronautics and Space Administration Headquarters 

Washington, D.C. 20546 

Research Foundation of SUNY at Stony Brook 

Stony Brook, NY 11794 

July, 1992 

PRINCIPAL INVESTIGATOR 

--- - 

Title: Associate Professor 

Dept.: Institute for Terrestrial and Planetary Atmospheres 

Telephone: (516) 632-8317 

(NASA-GW-190586) ANALYSIS OF EUV OAYGFOW N92-2945 1 

SPECTRA OF TRITON, TITAN AND EARTH Annual 

Progress Report {State Univ- of Hew York) 

22 P tlnc l a+ 

G3/91 0110083 
Abstract 

We have begun our studies of Titan and Triton by setting up a coupled ion and 

neutral chemical model of the ionosphere and thermosphere of Titan. The chemical scheme 

employs over 100 reactions and 46 species. Transport by diffusion and eddy diffusion 

of neutrals is included along with ambipolar diffusion of ions. We have computed the 

photoionization, photodissociation, electron impact excitation and ionization rates for the 

most important species, and the densities of ions and neutrals for a dayside model. We 

have computed the heating rates as a function of altitude and the heating efficiencies. We 

find that the heating efficiency in our standard model varies from about 30% near 800 km 

to 22% near 2000 km. We report here also on some photoelectron impact excitation rates 

for band systems of N2 in the Titan atmosphere. In the future, we propose to polish and 

publish our model, extend it to Triton, and look into excitation and emission of the Nz 

and Nz band systems. 
Progress Report 

In the last year, Roger Yelle and I have modeled the thermosphere and ionosphere 

of Titan, with a view toward determining the ionospheric structure, altitude profiles of 

minor neutral species, and the EUV heating efficiencies. Heating efficiencies are important - 

in determining the neutral temperature structure and thus the chemical structure of the 

thermosphere. The ionospheric and neutral structures are important for computing the 

airglow intensities. Our neutral model includes the N2 and CH4 density profiles from 

Voyager solar occultation data [Smith et aI., 19821; we adopted the densities of ethane 

(c2H6), ethylene (C2H4), and acetylene (C2H2) from the photochemical calculations of 

Yung et al. [1984]. The initial neutral atmosphere is shown in Figure 1. Our chemical 

scheme has included 108 reactions, 24 neutral species and 22 ions. The neutral species that 

are computed in the model are H, Hz, C, CH, 3CH2, 'CH2, CH3, Cz, CzH, CzHg, C2H5, N, 

N('D), NH, CN, HCN, HZCN, CHCN, HC3N, C2N, HC2N2, C3N, H2C3N, and C4N2. The 

ions include H+, H', H:, C+, CH', CH:, CH:, CH:, C~H;, C2H:, C2H:, C2H:, N+, 

HCN' , Hz CN+, ~f , N2H+, c:, C2Hf, C2~: and a pseudo-ion that represents all other 

hydrocarbon ions, C.H:. The ion-molecule ieactions were taken from the compilations 

of Anicich and Huntress [1986], Ikezoe et al. [1986), and more recent references. The 

rate coefficients for the dissociative recombination reactions have been fully updated. The 

calculation includes diffusion and eddy diffusion of neutrals and ambipolar diffusion of 

ions. Before we submit these results for publication, probably this September or October, 

we will expand the ion list to include NH+, NH:, NH$ and NH~. 

We have adopted the F79050N solar fluxes of Hinteregger [private communication; see 

also Torr et al., 19791, which is appropriate to a period of high solar activity, such as that 

which prevailed at the time of the Voyager 1 and 2 encounters with Saturn and Titan (1980- 

1981). The solar zenith angle in our model is 60'. Photoionization and photodissociation 

are included for N2, CHI, C2H6, C2H4, C2H2, and Hz, as well as photoionization of H, 

N and C. In addition, photoionization of CH3 by Lyman alpha, and photodissociation of 

HCN are also included. Electron impact excitation and ionization are included for Nz, CH4, -. -, 

Ha, H, C and N. The cross sections for photoionization and dissociative photoionization 

of N2 from threshold to 116 A were taken from Samson et al. [1987). The N2 electron 

impact cross sections are the same as those adopted by Fox and Victor [I9881 in their 

study of electron energy deposition in N2 gas. The cross sections for photoionization of 

hydrocarbons, and electron impact on Hz, H and CH4 are the same as those compiled by 

Kim and Fox [1990]. The cross sections for photodissociation of HCN were taken from 

Nuth and Glicker [I9821 and Lee [1980]. The cross sections for photoionization of C and 

N were taken from LeDourneuf et al. [1976], Cantu et al., (19811, and Daltabuit and 

Cox [1972]. The electron impact ionization cross sections for C and N were adopted from 

the measurements of Brook et al. [1978]. The ionization potential of CH3 is 9.84 eV, 

and photoionization by solar Lyman alpha is possible, but the cross section has not been 

computed or measured. We assume, as did Strobe1 [1975], that the cross section is equal 

to that of atomic carbon at threshold, 1.2 x 10-"cm2. 

Ion Production Rates. Altitude profiles of the production rates of the six major 

ions are shown in Figure 2. N2 is the major ion produced below about 1650 km, and 

CH: is the major ion produced above that altitude. At the ion peak, Nt. is the second 

most important ion produced, largely as a result of dissociative ionization of N2. Below 
about 950 km, C2Hf is the second most important ion produced. Its major source is 

photoionization of C7H4. CH~ is produced by photodissociative ionization of CHI, C2H4, 

and C2Hs, electron impact dissociative ionization of CH4, and photoionization of CH3 by 

Lyman alpha. The most important source of CH: is photodissociative ionization of CH4, 

with a column integrated rate of 3.1 x 107cm-2s-1, but photoionization of CH3 by Lyman 

alpha is comparable, with an integrated rate of 1.6 x l~~cm-~s-'. 

Because N2 has a very high ionization potential (15.58 eV) (as shown in Table l), the 

ion will react to produce ions whose parent neutrals have lower ionization potentials. Thus 

we do not expect or observe N: to be the terminal ion. N: reacts rapidly with methane, 

with acetylene, 

and with H2 

Figure 1. Neutral atmospheric model of Titan that is employed in the calculations. 
The product ions then react further, transforming the ionosphere to that shown in 

Figure 3. In our model H~CN+ is the major ion below about 1200 !:m; CH: is more 

important at higher altitudes. This is in contrast to the model of Ip (19901, in which N: 

was the dominant ion above 1400-1500 km. The source of the discrepancy is not obvious, 

but we believe our model to be superior to that of Ip, which is a photochemical equilibrium 

model and contains some outdated rate coefficients. The major source of H2CN+ at the 

ion peak is the proton transfer reaction 

C2H;C + HCN + H2CN+ + C2H4. 

The analogous reaction of C2Hl is the also important. 

- 3 - 2 - 1 1 

LOG ION PRODUCTlON lU'TE(srn-'rg) 

Figure 2. Altitude profiles of the production rates of the most important ions in the Titan 

ionosphere. 
1 BOO 

.5 1 1.5 2 2.5 3 3.5 4 

LOG ION DENSITY (~rn-~) 

Figure 3. Altitude profiles of the densities of the most important ions in the Titan ionosphere. 

+. PD=Photodissociation - 

- 

NN=Neutral-Neutral Rxns - 

- 

IM=Ion-Molecule Rxns - 

- 

EI=Eiectron-Impact Dissociation - 

- 

DR=Dissociative Recombination - 

- 

- 

- 

- 

- 

- 

- 

- 

- - 

- 

- 

- 

- 

- 

\I I I 

- 

1 2 -3 -? Log Heating Rate (eV cm s ) 

Figure 4. Altitude profiles of the heating rates of the most important processes in the 

Tit an thermosphere. 
EUV Heating Emciencies. 

The heating efficiency is the fraction of solar energy absorbed that is deposited locally 

as heat. The EUV (-100-1000 A) and FUV (-1000-2000A) regions of solar spectrum 

are absorbed in the thermospheres of planets. Solar energy is transformed to heat in photodissociation and photoelectron impact dissociation of molecules, in exothermic reactions, 

including ion-molecule reactions, neutral-neutral reactions, and dissociative recombination 

of ions with electrons. 

In photodissociation, the amount of energy that goes into kinetic energy is the difference between the energy of the photon and the dissociation energy (which may include 

some internal excitation of the fragments). In the absence of information about the electronic states of the fragments, they are assumed to be produced in their ground states. 

When there are molecular products, some of the energy may be taken up as vibrational 

energy of the fragments. The energy that appears as vibrational excitation in photodissociation has been found to be small [cf. Fox, 1988 iind references therein]; this would 

be expected to be especially true when the fragments are H atoms. We assume here that 

25% of the excess energy appears as vibrational energy of molecular products, and the 

remainder is converted to kinetic energy, as we have in previous calculations of heating 

efficiencies [e.g. Fox, 19881. A half-collision model suggests, however, that when one of 

the fragments is very light, such as a hydrogen atom or molecule, the energy that appears 

as vibrational excitation of the other fragment may be very small. For our final calculation, we will probably assume that only 10-15% of the energy is taken up as vibrational 

excitation in photodissociation. 

Although No is the major species in the atmosphere, its dissociation threshold is 

large, 9.76 eV, and, because most of the dissociation occurs through discrete excitation 

into predissociating states in the singlet manifold, it doesn't absorb longward of 985 A. 

The peak heating rate due to photodissociation of N2 is only 5.7 ev~m-~s-' at about 

1060 km, near the ionospheric peak. CHI is a strong absorber, and photodissociation 

of CH4 is the most important heating process of this type. The peak heating rate is 

about 1.4 x 10~eVcm-~s-' at 770 km. Although at this altitude infrared heating is more 

important than solar heating, the dominance of heating due to methane photodissociation 

extends to higher altitudes. At 1060 km, the heating rate due to methane photodissociation 

is 1.23 x 10' eV~m-~s-'. Even HCN photodissociation is more important than that of N2, 

with a heating rate of about 8 ev~m-~s-' at 1060 km. 

The energy released in exothermic reactions can appear as kinetic energy of the products, thus resulting in heating. Dissociative recombination reactions in particular are often 

very exothermic and contribute significantly to heating. On Mars and Venus, dissociative 

recombination of the major ion, 0:) is the most important chemical heat source for the 

neutrals [Fox and Dalgarno, 1979, 1981; Fox, 19881. On the Earth, dissociative recombination of NO+ is the most important heat source of ground state reactions [Torr et al., 

19801. On Titan, we find that dissociative recombination is not as important as it is on 

the terrestrial planets, partly because the ions are "processed" more, that is, they have 

undergone more transformations before they recombine. More important, however, is the 

presence of methane, which is a strong absorber, increasing both the heating rate due to 

photodissociation and the production rate of neutral fragments that can participate in 

neutral-neutral reactions compared to the terrestrial planets. 
In dissociative recombination of polyatomic molecular ions, as in photodissociation, 

some uncertainty exists about how much of the exothermicity appears as vibrational excitation of the molecular products. And just as for photodissociation, a half-collision model 

suggests that little energy is expected to be deposited as vibrational excitation. Although 

we have assumed that 25% of the energy released appears as vibrational energy of molecular fragments, we may reduce that number for the final calculation. The most important 

dissociative recombination reaction for neutral heating is that is of major ion, H2CN+, 

which actually has the structure HCNHf. There are four exothermic product channels for 

this reaction: 

HCNH' + e -, HCN + H 

-+ Hz + CN. 

The only information that is available about the product channels is the measurement of 

Adams et al. [1991], that indicated that 0.63 H atoms are produced per recombination. 

This implies that the sum of the branching ratios for the first two channels is 63% and 

the sum of the second two branching ratios is 37%. We somewhat arbitrarily assume that 

production of HCN, the more stable isomer, is the dominant channel of the first two, and 

that the third channel is more important than the fourth. 

In electron impact dissociation some of the energy lost by the electron may appear as 

kinetic energy of the neutrals produced. In general, the fraction of energy that appears 

as kinetic energy is not constant for a given process and it is therefore not possible to 

determine the heating due to electron impact dissociation exactly. An average value may 

be determined from time-of-flight studies, or derived from electron energy loss spectroscopy, 

but measurements are not available for all of the electron impact dissociations. Fortunately, 

Prokop and Zipf (19821 have measured the average kinetic energy of the N atoms that are 

released in electron impact dissociation and dissociative ionization of N2, and report values 

of 0.45 eV and 3.0 eV, respectively. Since this is the most important species in the Titan 

atmosphere, it accounts for a most of of the electron energy loss at the ion peak, near 

1000 km. In computing the heating due to electron impact dissociation, we have adopted 

the measured values for N2, and we have assumed a value of 1.0 eV per dissociation or 

dissociative ionization of H2 and CHI. 

In ion-molecule and neutral-neutral reactions, the exothermicity can appear as internal 

energy of the products, aa well as kinetic energy. In general, little information is available 

about the partitioning of energy among the various modes. For our standard calculation, 

we have assumed that 60% of the energy appears as vibrational energy of the products. 

We also then compute lower and upper limits to the heating efficiency using the values 

80 and 40%, respectively. For ion-molecules reactions, the partitioning of kinetic energy 

between the the neutral and the ion product is determined by momentum conservation. 

The most important ion-molecules reactions for thermospheric heating are 

and 
The most important neutral-neutral reactions are: 

and 

NH+N-+N2+H. 

The heating rates as a function of altitude are presented in Figure 4 and resulting 

heating efficiencies are shown in Figure 5. The standard values vary from about 30% at 

800 km to 22% at 2000 km. The lower and upper limits are about smaller and larger by 

about 0.05 near 800 km and converge to nearly the standard value at 2000 km. These 

heating efficiencies are very different from those appropriate to Earth, which are in excess 

of 50%, and are more like those for Venus and Mars, which are about 20-24%. It is 

apparent that in N2 atmospheres, it is the minor species that dominate the absorption and 

heating: O2 for the terrestrial case, and methane for Titan. 

Our major contribution at Stony Brook has been compiling the cross sections for 

photoprocesses and electron impact processes, calculation of the photoionization and photodissociation rates of the major and minor neutral species, calculation of the photoelectron 

impact production rates, as well as updating the tentative chemical reaction list provided 

by R. Yelle with more recent rate coefficients. YeUe wrote the chemistry code. We also 

computed the heating efficiencies from the ion and neutral reaction rate list provided by 

Yelle, added the heating due to photoelectron impact, photodissociation, and determined 

estimates for the amount of energy that goes into vibrational excitation of molecular products. 

2000 

800 I 

0 .1 .2 .3 .4 .5 

Heating Efficiency 

Figure 5. Altitude profiles for the heating efficiencies for solar radiation in the 14-2000A 

interval. The standard, upper limit and lower limit profiles are illustrated. 
Future Work 

During the next year, we would first like to polish and publish our model of the Titan 

ionosphere-thermosphere, including the reactions of NH+, NH:, NH:, and NH:, and to 

do a literature search to be sure that we have included all relevant odd nitrogen reactions, 

Once we are confidant that our model is the best that we can construct, then we will move 

on to do more detailed dayglow calculations. 

The ultraviolet spectrometers on Voyagers 1 and 2 measured emission from the Titan 

atmosphere in the range 500-1700 A, and the spectrum was found to be dominated by 

emission of N2 and N [Strobel and Shemansky, 19821. The most intense features of N2 were 

the c;'C$ -+ X'C: Rydberg bands, but the Birge-Hopfield (blIIu - X'C:) and LymanBirge-Hopfield (alIIg + XIZ:) bands were also present in the spectrum. The former two 

band systems are dipole allowed, and could be excited by fluorescent scattering, but the 

predicted intensities are small [Strobel and Shemansky, 19821. The emissions have been 

found to be brightest in the quadrant facing into the corotating magnetosphere of Saturn, 

and it has therefore been suggested that the emissions could be produced by impact of 

low energy electrons from Saturn's magnetosphere (Strobe1 and Shemansky, 1982 . Other 

features identified include the 1134-, 1200- and 1243-A lines of N and the 1085- 1 line of 

N+. Voyager 2 measured ultraviolet emissions from Neptune's satellite Triton. The spectra 

are similar. The strong emission at Lyman alpha in both spectra results from resonance 

scattering by thermospheric and exospheric atomic hydrogen. 

We will first model the nitrogen band systems using only solar and photoelectron 

excitation. We have already done such calculations for the Nz Vegard-Kaplan (A3X$ -+ 

X1 El), second positive (C311u -+ B311g), Lyman-Birge-Hopfield (a1 IIp 4 XI C:), first 

positive (B311g -r A3C:), reverse first positive, and W3Au -r B31Tg band systems on 

Venus and Mars [Fox et al., 1977; Fox and Dalgarno, 1979; 1981; Fox, 19921. A product 

of the photoelectron energy deposition calculation is a determination of the integrated 

rates for production of the excited triplet and singlet states of Nz. The predicted column 

integrated rates for the triplet states and the alIIg state (the upper state of the LymanBirge-Hopfield band system) are shown below: 

State Integrated Production Rate (106cm-zs-1) 

These calculations indicate that an ultraviolet spectrometer, with a channel in the 

near UV, would observed substantial intensities of the Vegard-Kaplan and second positive 

bands. Electron impact can account for about two-thirds of the measured Lyman-BirgeHopfield bands, although absorption by methane will modify that number. We will modify 

existing codes to predict the intensities of the individual bands, including absorption. 
Of the band systems arising from the states listed above, only the Lyman-BirgeHopfield bands appear in the FUV. Also, the strong emission from the N2 Rydberg bands 

that are seen in the Titan airglow is not observed on any of the terrestrial planets. This is 

because the ci state has a small but finite predissociation probability, which, in an optically 

thick situation, such as the Earth's thermosphere, leads ultimately to dissociation rather 

than to emission. Hence it has been inferred that the Rydberg bands must be produced at 

high altitudes on Titan [Strobel and Shemansky, 1982; Conway, 19831. More information 

is available now about the cross sections for electron impact excitation of N2 band systems 

[e.g., Ajello et al., 1989; James et a1.,1990; Tripp et al., 19901. In addition, the cross 

sections used by Strobe1 and Shemansky I19821 have been revised downward by a change 

in the calibration standard by Shemansky et al. [I9851 and Woolsey et al. [1986]. 

The N: Meinel and first negative bands may be produced by photoionization, electron 

impact ionization, and fluorescent scattering of radiation. N: is probably vibrationally 

excited at high altitudes in the ionospheres of Titan and Triton. We will model the ~f 

vibrational distribution, just as we and others have done for Earth [Broadfoot et al., 1967, 

1971; Degen, 1977, 1981; Fox and Dalgarno, 19851, Mars [Fox and Dalgarno, 19831 and 

Venus [Fox, unpublished calculation; see Fox, 19911. The vibrational distribution can 

be important for modeling the chemical and thermal structure, as well as determining 

the intensities of N: emissions. Noren et al. 119891 have recently suggested that rate 

coefficients for dissociative recombination of ground state ~,f is a factor of five slower than 

that of excited states, although this contradicts the more recent calculations of Guberman 

[1991]. Guberman did point out, however, that the yield of N('D) may vary dramatically 

with vibrational excitation. In order to model the high altitude ion distributions or the 

yields of metastable N atoms, it is necessary to know the vibrational distribution of N:. 

Loss of the ion will be via dissociative recombination in the upper part of the ionosphere. 

In the lower ionosphere charge transfer or atom/ion interchange reactions with neutral 

species may dominate, and the rates of, those reactions can also depend on the vibrational 

level of the ion. For example, if the Ar densities are significant (1-2% or more) a major 

production reaction for Arf should be charge transfer from vibrationally excited N:, just 

as we have found for the terrestrial ionosphere [Fox, 19861 and for Mars [Fox, unpublished 

calculations]. 

In the ionospheres of the terrestrial pIanets, fluorescent scattering of solar radiation 

in the N: Meinel and first negative band systems is the dominant factor in producing a 

non-LTE vibrational distribution for roadfoot foot, 1967; Degen, 1977; Fox and Dalgarno, 

1983; 19851 On Titan, fluorescent scattering will also be important, but we expect that 

at times when the atmosphere of Titan is within Saturn's magnetosphere (or interacts 

directly with the solar wind), electron induced fluorescence will also play a major role, 

as Degen [I9811 showed for terrestrial aurorae. Because of the high ionization potential 

of Nz, chemical reactions are not likely to play a major role in producing vibrationally 

excited N$. Nor do we expect collisional excitation to be as important in producing 

vibrationally excited N$ as it is in the ionospheres of the terrestrial planets, mostly because 

the temperatures are lower. Strictly speaking, however, it is the ion temperature that is 

important in determining collisional excitation rates and although the neutral temperatures 

are low, the ion temperatures may not be. A Nagy [private communication] is computing 

the ion temperatures on Titan, so those numbers should be available soon. We also expect 
the N$ at the peak on Titan to be more vibrationally excited than at the Fl peak on 

Earth. Since the scale height of Nz in the Titan thermosphere is large (70-100 km), the 

maximum ionization occurs in a region of lower total density. Therefore, the N;(V > 0) 

that are produced will be less efficiently quenched. 

The obvious next step is to do the analogous model for Triton, which has an atmosphere of similar composition: N2 plus hydrocarbons. The interaction of electrons from 

Neptune's magnetosphere with Triton's atmosphere, however, seems to be more important 

for producing the observed ionosphere and N2 emissions (Majeed et al., 1990; Summers and 

Strobel, 1991; Stevens et al., 19921 than electrons from Saturn's magnetosphere are to the 

Titan ionosphere and emissions. We will first run a solar model to constrain the amount 

of electron precipitation that is necessary for producing the ionosphere and powering the 

dayglow. We will then model the electron energy deposition using an electron transport 

code developed by H. S. Porter, that we have successfully used to model the Jovian and 

Venusian auroras. 

Table 1. Ionization Potentials 

Species IP (eV) Reference 

N2 

CH4 

CH3 

'332 

CH 

C2 H 

CzHa 

ClH4 

HCN 

HCNH (cis) 

HCNH (trans) 

Nesbitt et al. [1991] 
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JANE LEE FOX 

Institute for Terrestrial and Planetary Atmospheres 234 Second Ave. 

and Department of Mechanical Engineering St. James, NY 11780 

State University of New York at Stony Brook (516) 862-8366 

Stony Brook, NY 11794-2300 

(516) 632-8317 

FAX (516) 632-8544 

(BITNET) JFOXOSBCCMAIL 

(INTERNET) JFOXQCCMAIL.SUNYSB.EDU 

Education: 

University of Michigan. B.S. in Chemistry with high honors and high distinction, 1973. 

William J. Branstrom Freshman Prize. Moses and Sophia Gomberg Scholarr~hips, 1971, 

1972. Nola Sauer Minnis Prize. James B. Angell Scholar, 1972, 1973, 1974. 

Phi Beta Kappa. Mortar Board (Senior Women's Honorary) 

Harvard University. Enrolled September, 1973. Ph. D. in Chemical Physics, November, 

1978. National Science Foundation Predoctoral Fellow, 1973-1976. Research Advisor: 

Professor Alexander Dalgarno. 

Employment: 

Harvard University. Teaching Fellow, Summer 1974, Fall 1974, Spring 1975, Fail 1975. 

Max Planck Institut fiir Stromungsforschung, Got tingen, FRG . Stipendiatin, Summer 

1977. 

National Science Foundation National Needs Postdoctoral Fellow, October 1978-October 

1979. Postdoctoral Advisor: Professor Michael McElroy. 

Center for Earth and Planetary Physics, Harvard University. Research Fellow in Atmospheric Physics, October 1978-January 1980. 

University of Illinois, Urbana, IL. Assistant Professor of Chemistry and Electrical Engineering. January, 1980-July, 1981. 

Smithsonian Astrophysical Observatory, Cambridge, MA. Physicist. July 1981-August, 

1984. July, 1985. 

State University of New York at Stony Brook, Stony Brook, NY. Assistant Professor of 

Atmospheric Sciences and Mechanical Engineering. September 1984-August 1987. 

State University of New York at Stony Brook, Stony Brook, NY. Associate Professor 

of Atmospheric Sciences and Mechanical Engineering. September 1987-December 1991 

Associate Professor of Atmospheric Sciences and Marine Sciences January, 1992-present 
Professional Activities: 

Member: American Geophysical Union. American Astronomical Society, Division of Planetary Sciences. 

Associate Editor, Journal of Geophysical Research, Space Physics, Jan. 1989- December, 

1992. 

Comet Rendezvous/Asteroid Flyby (CRAF) Review Panel. Houston, Feb. 1986. 

NASA Planetary Atmospheres Review Panel, July 1989. 

Referee for Workshop IX.2 "The Venus Ionosphere" at the biannual meeting of COSPAR 

(Commit tee on Space Research) Espoo, Finland, July, 1988. 

Co-chairman of "Atmosphere and near space environment of Venus" session at Spring 

Meeting of the American Geophysical Union, May 1987. 

Chairman of "Venus magnetosphere and ionosphere" session at Fall Meeting of American 

Geophysical Union, San Francisco, Dec. 1989. 

Co-organizer (with W. Hoegy) of special session, LLPioneer Venus: Ready for final encounter" held at Spring Meeting of the AGU, Montreal, May, 1992. 

Member of the Planetary Atmospheres Management Operations Working Group, 1992- 

1994. 

Co-Convenor (with A. Nagy and D. J. Southwood) of Symposium 3.10 "Planetary Atmospheres and Magnetospheres" at the bi-annual meeting of the International Association 

of Geomagnetism and Aeronomy to be held in Argentina, August, 1993. 

Reviewer of proposals to NASA, NSF, Army Research Office. 

Reviewer of manuscripts to J. Geophys. Res., Geophys. Res. Lett., Icarus, Adv. Space 

Res., Rev. Geophys., J. Phys. Chem. 

6 invited review articles (4 published and 2 in preparation) 

Publications: 

Refereed Journals: 

Fox, J. L., A. Dalgarno, and G. A. Victor, The absorption of energetic electrons by 

argon gas, Planet. Space Sci., 25, 71, 1977. 

Fox, J. L., A. Dalgarno, E. R. Constantinides, and G. A. Victor, The nitrogen dayglow 

on Mars, J. Geophys. Res., 82, 1615, 1977. 

Fox, J. L., and A. Dalgarno, Radiative transition probabilities of the 1s2~'~P and 

1s2~"D states of the lithium isoelectronic sequence, Phys. Rev. A 16, 283, 1977. 

Fox, J. L. and A. Dalgarno, Electron energy deposition in carbon dioxide, Planet. Space 

Sci., 27, 491, 1979. 
Fox, J. L., and A. Dalgarno, Ionization, luminosity and heating of the upper atmosphere 

of Mars. J. geophy~. Res. 84, 7315, 1979. 

Fox, J. L., and A. Dalgarno, The production of nitrogen atoms on Mars and their escape, 

Planet. Space Sci., 28, 41, 1980. 

Fox, J. L., and A. Dalgarno, Ionization, luminosity, and heating of the upper atmosphere 

of Venus, J. Geophys. Res., 86, 629-639, 1981. 

Fox, J. L., and G. A. Victor, O++ in the Venusian Ionosphere, J. Geophys. Res., 86, 

2438, 1981. 

Fox, J. L., S. C. Wofsy, M. B. McElroy and M. J. Prather, A stratospheric chemical 

instability, J. Geophys. Res., 87, 11,126, 1982. 

Fox, J. L., The chemistry of metastable species in the Venusian ionosphere, Icaru~, 51, 

248, 1982. 

Fox, J. L., Atomic carbon in the atmosphere of Venus, J. geophys. Res. 87, 921 1, 1982. 

Erratum in J. Geophys. Res., 90, 11106, 1985. 

Fox, J. L., and A. Dalgarno, Nitrogen escape from Mars. J. geophys. Res. 88, 9027, 

1983. 

Wetmore, R. W., J. L. Fox, and A. Dalgarno, Radiative lifetimes of the second negative 

system of o:, Planet. Space Sci., 32, 11 11, 1984. 

Fox, J. L., and A. Dalgarno, The vibrational distribution of N: in the terrestrial ionosphere. J. geophys. Res. 90, 7557, 1985. 

Fox, J. L., The 0: vibrational distribution in the Venusian ionosphere, Adv. Space 

Res., 5, 165, 1985. 

Fox, J. L., The 0: vibrational distribution in the dayside ionosphere, Planet. Space 

Sci. 34, 1252, 1986. 

Fox, J. L., Ar+ in the terrestrial ionosphere, J. Geophys. Res., 91, 1731, 1986. 

Fox, J. L., Models for aurora and airglow emissions from other planetary atmospheres, 

INVITED paper based on presentation at the 1985 IAGA meeting in Prague, Can. 

J. Phys. 64, 1631, 1986. 

Fox, J. L., and G. A. Victor, Electron energy deposition in N2 gas, Planet. Space Sci., 

36, 329, 1988. 

Fox, J. L., Heating efficiencies in the thermosphere of Venus reconsidered, INVITED 

article for the special issue of Planetary and Space Science in honor of A. Dalgarno 

on the occasion of his 60th birthday, Planet. Space Sci., 96, 37, 1988. 

Fox, J. L., and J. H. Black, Photodissociation of CO in the thermosphere of Venus. 

Geophys. Res. Lett. 16, 291, 1989. 

Fox, J. L. and A. Dalgarno, Franck-Condon factors and transition probabilities of the 

second negative band system of O:, J. Geophys. ReJ., 11 19, 1990. 
Fox, J. L., The red and green lines of atomic oxygen in the nightglow of Venus. Adv. 

Space Res. 10 (5), 31, 1990. 

Fox, J. L. and H. A. Taylor, Jr., A signature of electron precipitation in the nightside 

ionosphere of Venus, Geophys. Res. Lett., 17, 1625, 1990. 

Kim, Y. H., and J. L. Fox, The Jovian ionospheric E region, Geophys. Res. Lett., 18, 

123, 1990. 

Fox, J. L. and S. W. Bougher, Structure, luminosity and dynamics of the Venus thermosphere, Space Sci. Rev., 55, 357-489, 1991. INVITED review for the special issue 

of Space Science Reviews on Venus Aeronomy, edited by C. T. Russell. 

Fox, J. L. and A. I. F. Stewart, The Venus ultraviolet aurora: a soft electron source. J. 

Geophys. Res., 96, 9829, 1991. 

Fox, J. L., Cross sections and reactions rates of relevezce to aeronomy, Rev. Geophys., 

April 1991 Supplement (U. S. National Report to International Union of Geodesy 

and Geophysic~), 1110-1131, 1991. INVITED contribution to the quadrennial US 

National Report to the IUGG. 

Kim, Y. H., J. L. Fox, and H. A. Porter, H: in the Jovian ionosphere: densities and 

vibrational distribution, J. Geophys. Res., 97, 6093, 1992. 

Fox, J. L., Production and escape of nitrogen atoms from Mars, J. Geophys. Res., 

(submitted), 1992. 

Fox, J. L., The production of hot oxygen at the exobases of the terrestrial planets. (in 

preparation), 1992. 

Fox, J. L., The nightglow of the terrestrial planets, INVITED review for Planet. Space 

Sci.. (in preparation), 1992. 

Fox, J. L., The chemistry of the Venus nightside ionosphere, INVITED article for the 

special issue of Planetary and Space Science honoring David Bates on the occasion 

of his retirement from editorship of the journal. (submitted May, 1992) 

Dalgarno, A. and J. L. Fox, Ion chemistry and physics of planetary interest, INVITED 

review article for Current Topics in Ion Cherni~try and Physics, (in preparation), 

1992. 

Refereed book chapters 

Fox, J. L., Dissociative recombination in aeronomy, in Dissociative Recombination: theory, experiment and applications edited by J. B. A. Mitchell and S. L. Guberman, 

World Scientific, Singapore, 1989 (INVITED). 

Fox, J. L., Airglow and aurora in the atmospheres of Venus and Mars, in Venu~ and 

Maps: Atmospheres, Ionospheres and Solar Wind Interaction (Geophysical Monograph 66), ed. J. G. Luhmann, Pepin, and Tatrallay, AGU Press, 1992, p. 191 

(INVITED). 
Other pubiication~: 

"Airglow", (INVITED) entry for Encyclopedia of Planetary Science, (submitted, 1992). 

Abstracts and presentations at meetings (since 1984): 

The vibrational distribution of 0: in the Venusian ionosphere, Bi-annual meeting of 

COSPAR, Graz, Austria, July, 1984. 

Ar+ in the terrestrial atmosphere, Fall meeting of the American Geophysical Union (AGU), 

San Francisco, Dec. 1984. 

Models for aurora and airglow emissions from other planetary atmospheres, INVITED talk 

at the 1985 meeting of the International Association of Geomagnetism and Aeronomy 

(IAGA), Prague, August 1985. 

The aurora on Venus, Fall meeting of the AGU, San Francisco, Dec. 1985. 

Electron energy deposition in N2 gas, Fall meeting of the AGU, San Francisco, Dec. 1986. 

The aurora on Venus. Presented to the Pioneer Venus Science Steering Group. March 

1985, Oct. 1985, April 1986, May 198'1, Nov. 1987. 

Heating efficiencies on Venus. Presented at meeting of the Pioneer Venus Science Steering 

Group, Oct. 1986. 

Heating efficiencies in the thermosphere of Venus reconsidered, AGU Spring meeting, 

Baltimore, May 1987. 

Particle precipitation and odd nitrogen in the nighttime thermosphere of Venus, AGU fall 

meeting, San Francisco, Dec. 1987. 

Dissociative recombination in aeronomy, INVITED talk at the International Symposium 

on Dissociative recombination: Theory, Experiment, and Applications, Lake Louise, 

Canada, May 1988. 

Excited states in aeronomy, INVITED talk at the Symposium on Atomic and Molecular Processes, with Application to Aeronomy and Astrophysics in honor of Alexander 

Dalgarno's 60th birthday, Cambridge MA, June 1988. 

The red and green lines of atomic oxygen in the Venus nightglow, Committee on Space 

Research (COSPAR) plenary meeting, Helsinki, July 1988. 

Solar photodissociation of CO in planetary atmospheres, AGU Fall Meeting, San Francisco, Dec. 1988. 

The neutral thermospheres of Mars and Venus, INVITED talk presented at the AGU 

Spring Meeting, Baltimore, May 1989. 

G. A. Victor, J. Raymond, and J. L. Fox, Electron energy deposition in oxygen plasmas, 

DAMOP meeting of the American Physical Society, May, 1989. 

A. I. F. Stewart and J. L. Fox, The Venusian aurora, abstract for the biannual meeting of 

the International Association of Geomagnetism and Aeronomy, Exeter, England, July, 

1989. 
Production of hot oxygen at the Venus exobase, presented to the Pioneer Venus Science 

Steering Group, Sept. 1989. 

A signature of auroral activity in the nightside ionosphere of Venus, AGU Fall Meeting, 

San Francisco, Dec. 1989. 

Airglow and auroral emission features on Mars and Venus, INVITED talk at the Chapman 

Conference on the Comparative Study of Venus and Mars: Atmospheres, Ionospheres 

and Solar Wind Interactions, Lake Balaton, Hungary, June 1990. 

S. W. Bougher and J. L. Fox, Comparative thermospheres: Venus and Mars, talk presented 

by S. W. Bougher at the Chapman Conference on the Comparative Study of Venus and 

Mars: Atmospheres, Ionospheres and Solar Wind Interactions, Lake Balaton, Hungary, 

June 1990. 

Chemistry of the nightside ionosphere of Venus, presented to the Pioneer Venus Science 

Steering Group, Sept. 1990. 

Chemistry of the nightside ionosphere of Venus, Annual Meeting of the Division of Planetary Sciences, American Astronomical Society, Charlottesville, Oct . 1990. 

The production of hot oxygen at the exobases of the terrestrial planets, AGU Fall Meeting, 

Dec. 1990. 

Particle precipitation in the atmospheres of Venus and Mars, INVITED talk presented at 

the biannual meeting of the International Union of Geodesy and Geophysics, Vienna, 

August, 1991. 

Nitrogen escape from Mars, presented at the Meeting of the Martian Surface and Atmosphere Through Time Program, Boulder, CO, September, 1991. 

The reaction O+ + C02 -+ 0; + CO in the Venus ionosphere, presented at the Pioneer 

Venus Science Steering Group, Ames Research Center, Mountain View, CA, October, 

1991. 

Heating efficiencies in the thermopshere of Titan, J. L. Fox and R. V. Yelle, Presented at 

the annual Meeting of the Division of Planetary Sciences of the AAS, Palo Alto, CA, 

November, 1991. 

Dissociative recombination in planetary ionospheres, INVITED presenation at the Second 

International Symposium on "Dissociative Recombination: Theory, Experiment and 

Applications" held in St. Jacut , France, May, 1992. 

Models of the Venus nightside ionosphere, presented at the Spring Meeting of the American 

Geophysical Union, Montreal, May, 1992. 

Production and escape of nitrogen atoms from Mars, presented at the Workshop on the 

evolution of the Martian atmosphere, Kona, June 1992. 

On A: density profiles in the Jovian auroral ionosphere, Y. A. Kim and J. L. Fox, Workshop on Time Variable Phenomena in the Jovian Atmosphere, Annapolis, July, 1992. 

Other presentations (not complete): 
The nitric oxide airglow in the Martian atmosphere, J. L. Fox and A. Dalgarno, Spring 

Meeting of the American Geophysical Union, May, 1977. 

O++ in the Venusian ionosphere, J. L. Fox and G. A. Victor, Spring Meeting of the 

American Geophysical Union, Toronto, May, 1980. 

The chemistry of metastables in the Venus ionosphere, International Conference on the 

Venus Environment, Palo Alto, November, 1981. 

A stratospheric chemical instability, invited talk to Joint Gas and Particulate Science 

Division and Chemical Kinetics Division Colloquium Series of the National Bureau of 

Standards, January, 1981. 

A stratospheric chemical instability, University of Michigan, Spring, 1981 (exact date 

unknown). 

Nitrogen escape from Mars, Second International Conference on Mars, (exact date unknown), 1981? 

A stratospheric chemical instability, Washington University, St. Louis, MO, (exact date 

unknown) 1982. 

A stratospheric chemical instability, Goddard Space Flight Center, (exact date unknown) 

1982. 

The escape of nitrogen from the Martian atmosphere, Center for Astrophysics Atomic and 

Molecular Physics Division Seminar, Cambridge, MA, February, 1982. 

Nitrogen escape from Mars, LPI Planetary volatiles conference, Alexandria, Minnesota, 

October, 1982. 

The 0: vibrational distribution in the terrestrial atmosphere, Fall meeting of the American Geophysical Union, San Francisco, December, 1983. 

Vibrational excitation in planetary upper atmospheres, (INVITED) Air Force Geophysics 

Laboratory, January, 1984. 

Vibrational excitation in planetary upper atmospheres, (INVITED) Goddard Space Flight 

Center, February, 1987. 

Vibrational excitation in planetary upper atmospheres, (INVITED) CONOCO lecture series, Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute 

of Technology, November, 1987. 

Heating efficiencies in the thermosphere of Venus, (INVITED) Air Force Geophysics Laboratory, January, 1988. 

Vibrational excitation in planetary upper atmospheres, (INVITED) Physical Chemistry 

seminar, SUNY-S tony Brook, February, 1989. 

The nightside ionosphere of Venus, (INVITED) Goddard Space Flight Center, May, 1990. 

Heating efficiencies in the thermosphere of Titan, (INVITED) University of California at 

Berkeley, Space Sciences Laboratory, November, 1991. 
Grants: 

Studies of the role of metastables and doubly ionized species in the chemical and thermal 

structures of the Venusian and Martian ionospheres, NASA Pioneer Venus Guest Investigator Grant. To University of Illinois, Dec. 1980-July 1981. To the Smithsonian 

Astrophysical Observatory, Nov. 1981-April 1982. 

Studies of the chemistry of vibrationally and electronically excited species in planetary 

upper atmospheres, NASA to the Smithsonian Astrophysical Observatory, Oct. 1983- 

Sept. 1984. 

Studies of the aurorally induced emissions on the nightside of Venus, NASA Pioneer Venus 

Guest Investigator Grant. To the Research Foundation of the State University of New 

York at Stony Brook (SUNY-Stony Brook), Jan 1985-July 1988. 

Studies of the chemistry of vibrationally and electronically excited species in planetary 

upper atmospheres, NASA Planetary Atmospheres Program, November 1984-January, 

1992 

Studies of the effects of vibrationally and electronically excited species in planetary upper 

atmospheres, NSF to the Massachusetts Institute of Technology, Sept. 1987-Oct. 1989. 

Studies of the chemistry of the nightside ionosphere of Venus, NASA Pioneer Venus Guest 

Investigator Grant, July 1988-November 1992. 

Exospheric processes and escape of species from the Martian atmosphere. NASA Martian 

Surface and Atmosphere Through Time Program, Nov. 1990-April, 1993. 

Analysis of EUV dayglow spectra for Triton, Titan and Earth, NASA Neptune Data 

Analysis Program. Joint with Roger Yelle (Arizona). July, 1991-June, 1992. 

Excited states in Planetary Aeronomy, NASA Planetary Atmospheres Program, January, 

1991-December, 1993 Equipment supplement. 

Travel grant from COSPAR to attend the Meeting in Graz, July 1984; SUNY-New Faculty 

Development Award, 1985; Travel Grant from the American Geophysical Union to 

attend the IAGA meeting in Prague, August 1985; SUNY Faculty Travel Grant to 

attend the IAGA meeting in Vancouver, August 1987 

Contracts: 

Studies of infrared aurorae (AFGL via Subcontract from Utah State University to the 

Smithsonian Astrophysical Observatory), March 1984-Sept 1985.