1. Joseph Ajello JPL Alan Heays Leiden Observatory
Titan Airglow: High Resolution Laboratory UV Spectroscopy for Cassini UVIS Model
Joseph Ajello
JPL
Alan Heays
Leiden Observatory
team meeting: June 2013

2. TITAN PROTON PLASMA (0.1 keV-4 MeV) & SOLAR XUV GENERATES 2-level IONOSPHERE (300-1500 KM)
Solar XUV Excitation –Strong Top Ionosphere
-Magnetospheric: p and O+ Plasma Sporadic low ionosphere (Cravens et al., 2008).
S. Pol
South SS. POLE shelf

3. N2 Cross section Analysis for Dayglow VI (2)→UVIS (16)→Lab(e +N2 500 features)
V(z)=g(z) x w MODEL
gj (z) = F (e) x n(z) x s(e)
Dl=0.2Å
Dl=30Å
Dl=5Å DD

4. ISS & UVIS OBSERVATION OF TITAN SOLAR ECLIPSE @ 600K km
UV- VIS-near IR ( ) nm N2 night glow to 1000 km
plasma + N2

5. EUV DARK SIDE RECORD 1 LIMB & DISK SPECTRA DOY110-2009 @15K km
-Spectrum =Eclipse at 20 x closer
-4-minute records
-Record 0 MRH = surface to 800 km
-Record 1;MRH = KM)
-NO Rayleigh scattering
Plasma excitation : km
-Molecular bands and NI ,II lines
-1/10 Intensity of Dayglow

6. High Resolution UV Spectroscopy for Cassini UVIS
GOAL AND RESULT:
Obtain BOTH High Resolution LABORATORY AND FIRST MODEL EUV Spectra of N2 by Electron Impact (FWHM= 0.2Å) to establish UV EMISSION CROSS SECTIONS .
AND Identify ~800 N2 (~500) and N I,II (~300) features (also under 16 features in Cassini UVIS Titan EUV Airglow Spectrum -FWHM 4Å).
Produce First Emission ab initio Quantum Model of Electron Excited Induced UV Fluorescence of N2 of 9 electronic states (b 1Πu, b' 1Σu+, c4' 1Σu+ c3 1Πu, o3 Πu, c4 1Πu, c5 1Πu, c5 '1Σu+ c6'Σu+  X 1Σg+ from eV for UVIS model. All UV Emission states are perturbed (>20% admixture) and weakly-to-strongly predissociated.
Determine from Laboratory Spectra Rotational Predissociation and Emission Yields for complete & accurate N2 model.

7. COMPARISON HIGH RESOLUTION LAB SPECTRUM & TITAN LOW RESOLUTION UVIS LIMB SPECTRUM
Lab Spectrum 0.2Å FWHM vs Titan Airglow 4-5Å FWHM
10-40 N2 Molecular Bands or NI,II lines per UVIS feature
16 UVIS features vs 800 Lab features ( Å)

8. Quantum Model (Coupled-Schroedinger Equation [CSE]) Based on High Resolution Laboratory Spectra
Observed 20 and 100 eV Lab Emission (black) Compared to CSE Model of N2 Excitation, Predissociation, & Fluorescence (red).
Output quantum-mechanical model simulates electron-impact excitation and fluorescence (grey = each band)– to aid the assignment of complex and blended UVIS spectrum.
Accurately Modeled optical excitation (hi energy)

9. Molecular emission from c4 ‘ 1S+u (0,0-12) to FUV
more members of c4' (0, v'') than previous
homogenous coupling
c4 ‘ 1S+u ~ b' 1S+u

10. Short EUV l shows Molecular N2+ X(0)+np Rydberg states Identified for First Time to n=9
c5(0,0–1) c6'‘(0,0–1)
c­6(0,0), c7'‘(0,0)
c­8(0,0) c9'(0,0) Resonances
2 valence states, 13 Rydberg states

11. 100 eV Emission Cross Sections of c 4'1S+u X 1S+g Rydberg bands
electron energies at Titan 10-(100 eV)
Q=1.1×
10-17 cm2
FCF vs b'~c4‘ coupling

12. Emission, Predissociation Cross Sections Five (n=3,4,5) Rydberg-Valence (12-15 eV) States of N2
Qex (10-19 cm2)
Qem(10-19 cm2)
Qpre (10-19 cm2)
c4' 1Su+
155a
115a
40a
b' 1Su+
128b
19.6
107.4a,e
b 1Pu
121b
9.7a
111.3a
c3 1Pu
161b
~1.7
159.3a
o3 1Pu
75b
~0.4
74.6a
totals
640
146
493
Average Predissociation) yield (Qpre/Qex) =77%, EUV photon yield=23%, 175K Titan).
Five singlet-ungerade states predissociate, eject fast N-atoms (>1 eV) of N(4So) + N(2Do) & N(4So) + N(2Po)