CALIFORNIA INSTITUTE OF TECHNOLOGY TIME DOMAIN TERAHERTZ SPECTROSCOPY OF POLYCYCLIC AROMATIC HYDROCARBONS Brandon Carroll  Marco A. Allodi  Sergio Ioppolo  Ian A. Finneran  Brett A. McGuire  Xander de Vries  Geoffrey A. Blake

Polycyclic Aromatic Hydrocarbons (PAHs) Nearly any combination of aromatic rings Stable with a wide variety of charge states, electronic states, and hydrogenation Highly photostable and functionalizable INTRODUCTION

Bands at 3.3 μ m 6- 9 μ m and μ m consistently appear together, however their relative intensities vary widely Transitions due to sp 2 hybridized (aromatic) carbonaceous species No one species can explain the observed variations in intensity or line shape/width UIRS

FAR INFRARED PAH EMISSION Boersma et al. ApJ , (2011)

SPECTRAL COVERAGE

EXPERIMENTAL SETUP

ANTHRACENE PELLETS

Three simple PAHs Crystalline samples Polyethylene substrate 0.3 THz – 8 THz Multiple temperatures –10 K, 37.5 K, 75 K, 150 K, 300K SPECTRA

NAPHTHALENE 4.9 THz

NAPHTHALENE 5.2 THz

NAPHTHALENE Frequency (cm -1 )

NAPHTHALENE Frequency (cm -1 ) Frequency (THz)

ANTHRACENE 2.5 THz

ANTHRACENE 3.3 THz

ANTHRACENE 7.0 THz

ANTHRACENE Frequency (cm -1 ) Frequency (THz)

ANTHRACENE Frequency (cm -1 ) Frequency (THz)

PYRENE 2.7 THz

PYRENE 5.7 THz

PYRENE Frequency (cm -1 ) Frequency (THz)

PYRENE Frequency (cm -1 ) Frequency (THz)

CONCLUSION AND FUTURE DIRECTIONS Initial spectra a promising Crystalline samples are promising, but complex Simple ab initio is a good start, but not complete

Si substrate Optical constants Lattice vibrations Additional species Matrix isolation CONCLUSION AND FUTURE DIRECTIONS Initial spectra a promising Crystalline samples are promising, but complex Simple ab initio is a good start, but not complete

ACKNOWLEDGEMENTS Blake Lab: -Jacob Good - Nate Crockett -Masha Klescheva -Coco Zhang -Dana Anderson -Katherine Kaufman -Alex Lockwood