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

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

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

ISS & UVIS OBSERVATION OF TITAN SOLAR ECLIPSE @ 600K km UV- VIS-near IR (200-1200) nm N2 night glow to 1000 km plasma + N2

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 = 800-1100 KM) -NO Rayleigh scattering Plasma excitation : 500-1200 km -Molecular bands and NI ,II lines -1/10 Intensity of Dayglow

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 12-15 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.

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 (800-1350 Å)

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)

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

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

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

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)