3-D SUBMILLIMETER SPECTROSCOPY FOR ASTROPHYSICS AND SPECTRAL ASSIGNMENT SARAH M. FORTMAN, IVAN R. MEDVEDEV, FRANK C. DE LUCIA, Department of Physics, The Ohio State University, Columbus, OH , USA. OSU International Symposium on Molecular Spectroscopy Columbus, OH June 16 th, 2008

Two Related Objectives Spectroscopy Challenge Bootstrap Assignment in Complex Spectra FASSST spectra may contain >10^5 lines in many vibrational states Traditional Approach Use 2D (intensity, frequency) spectra to assign and bootstrap in each vibrational state New Approach Observe intensity calibrated variable temperature spectrum and calculate lower state energies. Use intensity, frequency and lower state energies in the bootstrap assignment Astronomy Challenge Current telescopes approach confusion limit Many unassigned lines New systems (Alma, Herschel) will be more powerful Traditional Approach Quantum Mechanical predictions of astrophysical spectra give intensity and frequency as a function of temperature Spectroscopists calculate and fit what we can, not what astronomers need New Approach Predict intensity and frequency as a function of temperature without assignment courtesy of J. Cernicharo Intensity Calibrated Variable Temperature Spectroscopy Observe 2D spectra at many temperatures Calculate intensity, frequency and lower state energies for assigned and unassigned lines Give astronomers what they want Give spectroscopists more information

FREQ ERR LGINT DR ELO GUP TAG QNFMT QN’ QN” Spectroscopic Challenge NEW PARAMETER (EST. ERROR) ( 0) ( 0) (307) (308) ( 35) ( 69) ( 33)E E (144)E E ( 48)E E (269)E E ( 60) (150)E E-03 Predicted lines from SPFIT.cat fileFitted Constants from SPFIT.fit file

Graphing in Two and Three Dimensions Frequency (MHz) Intensity (nm2*MHz) Lower State Energy (cm-1) Traditional approach uses a 2D (intensity vs. frequency) plot New approach creates a 3D plot from the intensity, frequency and lower state energy data

Interference fringes Spectrum InSb detector 1 InSb detector 2 Ring cavity: L~15 m Mylar beam splitter 1 Mylar beam splitter 2 High voltage power supply Slow wave structure sweeper Aluminum cell: length 6 m; diameter 15 cm Trigger channel /Triangular waveform channel Signal channel BWO Magnet Lens Filament voltage power supply Length ~60 cm Stepper motor Reference channel Lens Stainless steel rails Path of microwave radiation Preamplifier Frequency roll-off preamplifier Reference gas cell Glass rings used to suppress reflections Data acquisition system Computer FAst Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer Thermal enclosure

Temperature Control Ran experiment once Temperature Range: 228 – 405 K (-45 – 132 °C) at ~.8 degrees/min Took 700 scans over 3.5 hours totaling 29.6 GB of data

Spectra as a Function of Temperature The physical basis of the calculation of the lower state energy is the differential change in line strength with temperature. Subset of Data (in total experiment 700 traces over 50 GHz)

Ratios to Obtain Lower State Energy We can plot the log of the ratio in log(1/T) space and expect to see a straight line. Scatter from the peak finder Ripples (variation in reflection with T?) Temperature calibration (currently thermocouples, starting to use spectroscopic temperature) Consider taking the ratio of two lines of which one is assigned and the other is unassigned.

Lower State Energy vs. Thermal Behavior Okay but not great

Astronomy The smallest errors in intensities will come when the calculated temperature is bounded by experimental temperatures The error in the predicted intensity will be of the order the error in the observations (or better because we make many observations). Propagation of Error and Uncertainties Spectroscopy We expect to reduce uncertainties by a factor of 10 by: Replacing the peak finder with analysis Fitting a model to the baseline ripple Using a grand fit of all assigned lines as the reference line instead of a single line Getting a proper average over the ends by using the spectroscopic temperature Operating over a larger temperature range (using a collisional cooling cell to 2K)