1. FAST SCAN SUBMILLIMETER SPECTROSCOPIC TECHNIQUE (FASSST). IVAN R. MEDVEDEV, BRENDA P. WINNEWISSER, MANFRED WINNEWISSER, FRANK C. DE LUCIA, DOUGLAS T. PETKIE, MARKUS BEHNKE, RYAN P. A. BETTENS, and ZBIGNIEW KISIEL

2. Overview TECHNIQUE  FAst Scan Submillimeter Spectroscopic Technique (FASSST).  Frequency measurements CHALLENGES  Line intensity measurements  Spectral predictions without assignment or analysis

3. 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

4. FASSST Attributes 1. Can record 10000-100000 resolution elements/sec Freezes Source Frequency Drift Freezes Chemistry Changes 2. Frequency measurement accuracy Typically ~ 30 kHz ( 1/10^7 at 300 GHz) 3. ‘Locally’ (~ 1 GHz) intensity measurement is flat to ~1% A basis for intensity measurement

5. 3 mm: 79750-115750 MHz Lines with T A >0.04 K = 2152; 504 are U = 23% 2 mm: 130000-178000 MHz Lines with T > 0.1 K = 4031; 1606 are U = 40% 1mm: 196750-281000 MHz Líneas con T>0.1 K: 7676 lines; 3281 are U = 43% Identification of the ‘U’ lines in the interstellar molecular spectra. Spectral predictions without assignment or analysis. Orion. IRAM 30-m telescope line survey

6. Large fraction of ‘U’ lines most likely corresponds to isotopologues and vibrational excited states of well known molecules like CH 3 OCH 3, CH 3 OH, methyl formate … To identify lines unambiguously we need to know their frequencies and intensities at the temperature of the observed interstellar region To predict the intensity we need to know the lower state energy and the transition dipole moment matrix element The proposed scheme allows us to make spectral predictions without assignment or analysis

7. Bootstrap Analysis of A and E Ground State Lines of Methyl Formate But this is only about 10% of lines

8. Prediction scheme Measure spectrum of the molecule at two temperatures Ratio the intensities of all spectral lines Given the lower state energy of a single previously assigned transition we can calculate lower state energies and relative intensities at the desired sample temperature for the frequency region where power profile of the spectrometer is known

9. The total number density (chemistry and pressure issues). But, for an unassigned line, one does not know -The matrix element -The lower state energy -The partition function Absorption Coefficients What You Need to Know to Simulate Spectra at an Arbitrary Temperature T 3 without Spectral Assignment

10. Consider two lines, one assigned and one unknown at two temperatures T 1 and T 2 Step 1: With Eqn. 1 for both the known and unknown line, we have two equations and two unknowns: 1. The number density and partition function ratio for the T 1 and T 2 lab measurements 2. The lower state energy of the unassigned line Step 2: Solve for the lower state energy of unassigned line Eqn. 1 Eqn. 2

11. Comparison of Energy Levels Calculated from Experimental and Quantum Calculations for SO 2

13. The Combined Equation

14. Comparison of Intensities Calculated from Experimental and Quantum Calculations for SO 2

15. Propagation of Uncertainty (T 2 = 300 K) T 1 = 77 K Collisional cooling

16. Summary and Conclusions From experimental measurements at two temperatures T 1 and T 2, it is possible to calculate spectrum (with intensities) at an arbitrary T 3. For low T 3, a relatively low T 2 improves the accuracy of the calculated spectrum. Collisional cooling provides a general method for achieving this low T 2, with 77 K convenient and suitable for all but the lowest temperatures. FASSST is a means of obtaining the needed data rapidly and with chemical concentrations constant over the data collection period.