1. Rotationally-Resolved Infrared Spectroscopy of the ν 16 Band of 1,3,5- Trioxane Bradley M. Gibson, Nicole C. Koeppen Department of Chemistry, University of Illinois Benjamin J. McCall Departments of Chemistry, Astronomy, and Physics, University of Illinois

2. Outline {2} 1.Motivation a)Instrumental Characterization b)Astrochemical Relevance 2.Spectrometer Design a)Layout and Performance b)EC-QCL c)Locking System 3.Spectroscopy of Trioxane a)High-Resolution Spectra b)Fitting and Ro-Vibrational Constants

3. Motivation {3} Instrument Demonstration Goals High spectral resolution - Dense spectrum, Q branch spacings ~ 30 MHz Strong absorber for supercritical fluid source - 220 km / mol for ν 16 band Astrochemical / astrophysical relevance - Polyoxymethylene – extended formaldehyde source in comets

4. Why study trioxane? Figures from:Cottin et al., J. Photochem. Photobiol. 135, 53 (2000). Rosetta mission poster, http://sci.esa.int/rosetta/53294-rosetta-mission-poster/ {4} Simple POM, photodegradation product Tracer for POM – volatile, strong absorber Presence could be confirmed by ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis)

5. Why study trioxane? Figures from:Oka et al., Bull. Chem. Soc. Jpn. 37, 4 (1964). Kobayashi et al., J. Chem. Phys. 44, 922 (1996). {5} Chair conformation, C 3v symmetric top Inversion possible, splitting not observed in rotational spectra Several microwave spectra, one ro-vibrational (ν 17 )

6. Spectrometer Design Figure from:Gibson et al., J. Mol. Spec., submitted 2015. {6}

7. What is an EC-QCL? Figure from:Wysocki et al., Appl. Phys. B: Lasers Opt. 92, 305 (2008). {7}

8. What is an EC-QCL? {8}

9. What’s the tuning range? Figure from:Gibson et al., J. Mol. Spec., submitted 2015. {9} FP-QCL EC-QCL

10. How stable is the laser? Standard deviation: 0.00437 cm -1 ( ~ 131 MHz) Figure from:B.M. Gibson et al., “Development of a Frequency-Stabilized Mid-Infrared External Cavity-QCL Cavity Ringdown Spectrometer ”. 69 th ISMS, 2014 {10}

11. How can we improve the stability? Tilt-Tuned Etalon Locking Lock laser to side of etalon fringe Tilting etalon changes FSR, moves fringes Laser follows the fringe, allowing tuning {11} 0°1°2°3°

12. How can we improve the stability? Locking to Ge etalon decreases jitter, increases long-term drift Enclosing etalon slows thermal drift Jitter reduced to ~ 1 MHz over one second integration Figure from:Gibson and McCall, Opt. Lett., 40, 2696 (2015). {12} Unlocked Locked, no enclosure Locked, w/ enclosure

13. Trioxane Spectroscopy Figure from:Gibson et al., J. Mol. Spec., submitted 2015. {13} PGOPHER simulation Experimental

14. Trioxane Spectroscopy Figure from:Gibson et al., J. Mol. Spec., submitted 2015. {14}

15. Trioxane Spectroscopy Figure from:Gibson et al., J. Mol. Spec., submitted 2015. {15} Average fitting residual ~ 34 MHz, limited by wavelength calibration Relative intensity accuracy limited by undersampling Tradeoff exists between frequency / intensity accuracy

16. Trioxane Spectroscopy Figure adapted from:Gibson et al., J. Mol. Spec., submitted 2015. {16}

17. Figure from:B.M. Gibson et al., “Development of a Sheath-Flow Supercritical Fluid Source for Vaporization of Nonvolatiles at Moderate Temperatures”. 68 th ISMS, 2013 What’s next? {17} Supercritical Fluid Source

18. Figure from:B.M. Gibson et al., “Development of a Sheath-Flow Supercritical Fluid Source for Vaporization of Nonvolatiles at Moderate Temperatures”. 68 th ISMS, 2013 What’s next? {18} Supercritical Fluid Source Finish constructing second-generation source Characterize rotational temperature with trioxane High Rep-Rate Ringdown Improve sensitivity by locking to ringdown cavity Attempt to observe C 60 absorption

19. Acknowledgements {19} McCall Group Gerard Wysocki