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

2. High Resolution UV Spectroscopy for Cassini UVIS
GOAL AND RESULT:
Obtain High Resolution Optically Thin Laboratory 20 and 100 eV Spectra of N2 by Electron Impact (FWHM= 0.2Å) wavelength range of 800 to 1350 Å to establish UV ab initio Emission Model Constants.
Identify ~800 N2 (~500) and N I,II (~300) features (same 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 1Σu+  X 1Σg+ from eV (+ a 1Πg  X 1Σg+ Lyman-Birge-Hopfield system) for UVIS model to ionization limit. 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.

3. 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)

4. 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)

5. 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)
c 1Su+
155a
119a
36a
b' 1Su+
128b
20.4
107.6a,e
b 1Pu
121b
6.9a
114.1a
c3 1Pu
161b
~0.7
160.3a
o3 1Pu
75b
~0.4
74.6a
totals
640
148
492
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)