1. EXPERIMENTAL LINE LISTS OF HOT METHANE Image credit: Mark Garlick MONDAY 22 nd JUNE 2015 ROBERT J. HARGREAVES rhargrea@odu.edu MICHAEL DULICK PETER F. BERNATH Department of Chemistry Old Dominion University Norfolk, VA 23529

2. TEMPERATURE RANGES 1000 2000 30004000 5000 6000 7000 8000 The Sun - 5800 K (e.g., CN, OH, CH, NH) Sunspots - 3200 K (e.g., H 2 O, TiO) Brown Dwarfs Stars Exoplanets/ H+H+ Diatomic Molecules Polyatomic Molecules Temperature / K H 2 O NH 3 CH 4 0 Planets M Dwarf Stars EARTH – 296 K HITRAN database HITEMPA

3. BROWN DWARFS  Characterized by their spectra  Not stars  No hydrogen fusion occurs  CH 4  Major source of opacity in brown dwarfs  Most abundant molecule in Jupiter and Saturn  Characterizes T dwarfs ~1400 K ~800 K Cushing et al. (2006), ApJ 648, 614 ML T Y JupiterG ~3500 K~2000 K ~1000 K ~300 K 160 K5700 K Stars Brown dwarfs Planets Sun Adapted from R. Hurt (Caltech/IPAC)

4. EXOPLANETS  CH 4 also a major feature of exoplanet transit spectra  Mainly have hot atmospheres  Also CO 2, H 2 O, CO Adapted from: Hand (2011), Nature 480, 302 Swain et al., (2008), Nature 452, 329 HD 189733b (T ~ 1100 K)

5. CH 4 POLYADS Adapted from: S. Albert et al. 2009, Chem. Phys. 356, 131 ModeDegeneracy Band Origin (cm -1 ) Type ν 1 (a 1 )12914 Symmetric C-H stretch ν 2 (e)21526Bend ν 3 (t 2 )33020 a Asymmetric C-H stretch ν 4 (t 2 )31306 a Bend T d symmetry a infrared active ν 1 ≈ ν 3 ≈ 2ν 2 ≈ 2ν 4

6. PREVIOUS WORK  Line parameters mainly at room temperature or below:  HITRAN 2012 database (Rothman et al. 2013)  Based on the line list from Brown et al. (2013)  HITEMP does not include CH 4  Campargue et al. (2013) - WKLMC empirical line lists  Hot experimental (emission) work:  Nassar & Bernath (2003)  Thiévin et al. (2008)  Hargreaves et al. (2013)  Ab initio theoretical line lists:  Rey, Nikitin & Tyuterev (2014) - RNT  0-5000 cm -1  Contains up to 11.5 billion transitions  T = 500, 1000, 1500 and 2000 K  Yurchenko & Tennyson (2014) - 10to10  Part of ExoMol project  Almost 10 billion transitions  Valid up to 1500 K

7. ASTRONOMICAL REQUIREMENTS  Square of transition dipole moment, S J’J’’  Partition function, Q T retrieved

8. FOUR SPECTRAL METHOD  Experimental method  Emission and absorption  Bruker FTS  0.02 cm -1 resolution  Tube furnace  Quartz cell  Record temperatures  Temperatures 24 – 900°C  Spectral range: 2500 – 5000 cm -1  Pentad and Octad  60 Torr methane  600 scans  Based on previous experience  Need 4 spectra per temperature

9. FOUR SPECTRAL METHOD 700°C 1: Hot CH 4 + Lamp (+ background T) 3: No sample + Lamp (+ background T) 2: Hot CH 4 + no lamp (+ background T) 4: No sample + no lamp (+ background T) 700°C

10. EQUILIBRIUM 1: Hot CH 4 + Lamp (+ background T) 2: Hot CH 4 + no lamp (+ background T) Optically Thin Optically Thick Demonstrates Kirchoff’s Law: ε = 1 – α

11. EMPIRICAL LOWER STATE ENERGIES  From line strength equation ( S’ ):  Rearranging to give:  Typically contain 25,000 lines  Calibrated to HITRAN PentadOctad

12. LINE LISTS AND CONTINUA  Line lists contain  Temperature  Position (cm -1 )  Intensity (cm molecule -1 )  Lower state energy (cm -1 )  But, also require cross section  cm 2 molecule -1  Harrison et al. (2010) PentadOctad

13. BROWN DWARF COMPARISON  T4.5 dwarf  2MASS 0559-14  1200 K  VSTAR  Versatile Software for Transfer of Atmospheric Radiation  Contains new CH 4 data  Low resolution  Continuum needed  Line lists ~ 25,000 lines  Compares well with 10to10  10 billion lines

14. OVERVIEW AT 700°C Observed Transmission at 700°C Simulated spectrum (new line list + continuum) HITRAN 2012 RNT 10to10 5000

15. HIGH RESOLUTION AT 700°C <0.1 ~ 0.5 x ? 0.15 0.1 >1.0 Simulated spectrum (new line list + continuum) HITRAN 2012 RNT 10to10 Observed Transmission at 700°C

16. SUMMARY  Hot empirical line lists and continua  Accounts for emission and absorption  Assignments are not necessarily needed for astronomical applications  Low resolution  Can be used to accurately model brown dwarf atmospheres  Continuum is crucial  Compares well with theoretical line lists  High resolution  Line positions more accurate than state-of-the-art theoretical data  Can be used to refine theory  High resolution data needed for latest observations  CRIRES observations R ~ 100,000  e.g., Snellen et al. (2010) Only data presented here performs well at both high and low resolution

17. Acknowledgements The work on the spectra of hot molecules has been funded by a NASA laboratory astrophysical grant. Thanks to the group of Peter Bernath at Old Dominion University and Jeremy Bailey (VSTAR model) at the University of New South Wales. THANKS FOR LISTENING