Keeyoon Sung

Submillimeter-wave and far-infrared spectroscopy of high-J transitions of the ground and ν2=1 states of ammonia

Complete and reliable knowledge of the ammonia spectrum is needed to enable the analysis and interpretation of astrophysical and planetary observations. Ammonia has been observed in the interstellar medium up to J=18 and more highly excited transitions are expected to appear in hot exoplanets and brown dwarfs. As a result, there is considerable interest in observing and assigning the high J (rovibrational) spectrum. In this work, numerous spectroscopic techniques were employed to study its high J transitions in the ground and ν(2)=1 states. Measurements were carried out using a frequency multiplied submillimeter spectrometer at Jet Propulsion Laboratory (JPL), a tunable far-infrared spectrometer at University of Toyama, and a high-resolution Bruker IFS 125 Fourier transform spectrometer (FTS) at Synchrotron SOLEIL. Highly excited ammonia was created with a radiofrequency discharge and a dc discharge, which allowed assignments of transitions with J up to 35. One hundred and seventy seven ground state and ν(2)=1 inversion transitions were observed with microwave accuracy in the 0.3-4.7 THz region. Of these, 125 were observed for the first time, including 26 ΔK=3 transitions. Over 2000 far-infrared transitions were assigned to the ground state and ν(2)=1 inversion bands as well as the ν(2) fundamental band. Of these, 1912 were assigned using the FTS data for the first time, including 222 ΔK=3 transitions. The accuracy of these measurements has been estimated to be 0.0003-0.0006 cm(-1). A reduced root mean square error of 0.9 was obtained for a global fit of the ground and ν(2)=1 states, which includes the lines assigned in this work and all previously available microwave, terahertz, far-infrared, and mid-infrared data. The new measurements and predictions reported here will support the analyses of astronomical observations by high-resolution spectroscopy telescopes such as Herschel, SOFIA, and ALMA. The comprehensive experimental rovibrational energy levels reported here will permit further refinement of the potential energy surface to improve ammonia ab initio calculations and facilitate assignment of new high-resolution spectra of hot ammonia.

Rotational spectroscopy as a tool to investigate interactions between vibrational polyads in symmetric top molecules: Low-lying states v8⩽2 of methyl cyanide, CH3CN

Author Institution: I. Physikalisches Institut, Univ. Koln, 50937 Koln; and MPIfR, 53121 Bonn, Germany; JPL, California Inst. of Technol., Pasadena, CA 91109, USA; LISA, Univ. Paris 12 \& Paris 7 \& CNRS, 94010 Cr{e}teil, France; PNNL, Richland, WA 99352, USA

Design and Construction of Absorption Cells for Precision Radial Velocities in the K Band Using Methane Isotopologues

We present a method to optimize absorption cells for precise wavelength calibration in the near-infrared. We apply it to design and optimize methane isotopologue cells for precision radial velocity measurements in the K band. We also describe the construction and installation of two such cells for the CSHELL spectrograph at NASA’s IRTF. We have obtained their high-resolution laboratory spectra, which we can then use in precision radial velocity measurements and which can also have other applications. In terms of obtainable RV precision, methane should outperform other proposed cells, such as the ammonia cell (^(14)NH_3) recently demonstrated on CRIRES/VLT. The laboratory spectra of the ammonia and methane cells show strong absorption features in the H band that could also be exploited for precision Doppler measurements. We present spectra and preliminary radial velocity measurements obtained during our first-light run. These initial results show that a precision down to 20-30 m s^(-1)can be obtained using a wavelength interval of only 5 nm in the K band and S/N ∼ 150. This supports the prediction that a precision down to a few meters per second can be achieved on late-M dwarfs using the new generation of NIR spectrographs, thus enabling the detection of terrestrial planets in their habitable zones. Doppler measurements in the NIR can also be used to mitigate the radial velocity jitter due to stellar activity, enabling more efficient surveys on young active stars.

PROGRESS IN THE MEASUREMENT ON TEMPERATURE-DEPENDENCE OF H2-BROADENING OF COLD AND HOT CH4

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; V. MALATHY DEVI, D. CHRIS BENNER, Department of Physics, College of William and Mary, Williamsburg, VA, USA; TIMOTHY J. CRAWFORD, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; ARLAN MANTZ, Department of Physics, Astronomy and Geophysics, Connecticut College, New London, CT, USA; MARY ANN H. SMITH, Science Directorate, NASA Langley Research Center, Hampton, VA, USA.

FT-IR measurements of mid-IR propene (C3H6) cross sections for titan stratosphere

We present temperature dependent cross sections of propene (C3H6; CH2-CH-CH3, propylene), which was detected in the stratosphere of Titan.a For this study, a series of high-resolution (0.0022 cm−1) spectra of pure and N2-mixture samples were recorded at 150 – 296 K in the 650 – 1530 cm−1(6.5 – 15.3 μm) at the Jet Propulsion Laboratory using a Fourier-transform spectrometer and a custom-designed cold cellbc. The observed spectral features cover the strongest band (ν19) with its outstanding Q-branch peak at 912 cm−1and three other strong bands: ν18, ν16 and ν7 at 990, 1442, and 1459 cm−1, respectively. In addition, we have generated a HITRAN-format empirical ‘pseudoline list’ consisting of line positions, intensities, and effective lower state energies, which were determined by fitting all the observed propene spectra simultaneously. A newly derived partition function was used in the analysis. The results are compared with early work from relatively warm temperatures (278 – 323 K).d

14NH3 LINE POSITIONS AND INTENSITIES IN THE FAR-INFRARED: COMPARISON OF FT-IR MEASUREMENTS TO EMPIRICAL HAMILTONIAN MODEL PREDICTIONS

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; SHANSHAN YU, Molecular Spectroscopy, Jet Propulsion Laboratory, Pasadena, CA, USA; JOHN PEARSON, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; OLIVIER PIRALI, AILES beamline, Synchrotron SOLEIL, Saint Aubin, France; F. KWABIA TCHANA, CNRS, Université Paris Est Créteil et Paris Diderot, LISA, Créteil, Val de Marne, France; LAURENT MANCERON, Beamline AILES, Synchrotron SOLEIL, Saint-Aubin, France.

Precise Near-Infrared Radial Velocities

We present the results of two 2.3 μm near-infrared (NIR) radial velocity (RV) surveys to detect exoplanets around 36 nearby and young M dwarfs. We use the CSHELL spectrograph ( R ~ 46,000) at the NASA InfraRed Telescope Facility (IRTF), combined with an isotopic methane absorption gas cell for common optical path relative wavelength calibration. We have developed a sophisticated RV forward modeling code that accounts for fringing and other instrumental artifacts present in the spectra. With a spectral grasp of only 5 nm, we are able to reach long-term radial velocity dispersions of ~20–30 m s −1 on our survey targets.

FT-IR MEASUREMENTS OF NH3 LINE INTENSITIES IN THE 60 – 550 CM−1 USING SOLEIL/AILES BEAMLINE

KEEYOON SUNG, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; SHANSHAN YU, Molecular Spectroscopy, Jet Propulsion Laboratory, Pasadena, CA, USA; JOHN PEARSON, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; LAURENT MANCERON, Beamline AILES, Synchrotron SOLEIL, Saint-Aubin, France; F. KWABIA TCHANA, LISA, CNRS, Universités Paris Est Créteil et Paris Diderot, Créteil, France; OLIVIER PIRALI, AILES beamline, Synchrotron SOLEIL, Saint Aubin, France.

FT-IR measurements of cold cross sections of benzene (C6H6) for CASSINI/CIRS

Titan’s stratosphere is abundant in hydrocarbons (CxHy) producing highly complicated and crowded features in the spectra of Cassini/CIRS. Among these, benzene (C6H6) is the heaviest hydrocarbon ever seen in the Titan and cold planets. For this reason, a series of pure and N2-broadened C6H6 spectra were recorded in the 640 to 1540 cm−1region at gas temperatures down to 231 K using a Fourier transform spectrometer (Bruker IFS-125HR) at the Jet Propulsion Laboratory. We report temperature dependent absorption cross sections for three strong fundamental bands (ν4, ν14, ν13). We also derived pseudo-line parameters, which include mean intensities and effective lower state energies on a 0.005 cm−1frequency grid, obtained by fitting all the laboratory spectra simultaneously. For the pseudoline generation, details can be found in a JPL MK-IV website, http://mark4sun.jpl.nasa.gov/data/spec/Pseudo). The resulting pseudolines of the strong bands reproduce observed cross sections to within ̃3 %. These new results are compared to earlier work, including the C6H6+N2 spectra recorded at PNNL.a b

The Oxygen A Band

D. CHRIS BENNER, V. MALATHY DEVI, JIAJUN HOO, Department of Physics, College of William and Mary, Williamsburg, VA, USA; JOSEPH HODGES, DAVID A. LONG, Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, MD, USA; KEEYOON SUNG, Jet Propulsion Laboratory, Science Division, California Institute of Technology, Pasadena, CA, USA; BRIAN DROUIN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA; MITCHIO OKUMURA, THINH QUOC BUI, Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA; PRIYANKA RUPASINGHE, Physical Sciences, Cameron University, Lawton, OK, USA.