Molecular Spectroscopy Symposium June 2011 TERAHERTZ SPECTROSCOPY OF HIGH K METHANOL TRANSITIONS John C. Pearson, Shanshan Yu, Harshal Gupta, and Brian J. Drouin, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

2 Molecular Spectroscopy Symposium June 2011 Methanol: A Perturbed History (1/3) Initial Methanol assignments –Required approximate solution of torsional problem First “complete” microwave analysis Lees & Baker 1968 –Approximate (few MHz) solution to low K E-state perturbations

3 Molecular Spectroscopy Symposium June 2011 Methanol: A Perturbed History (2/3) Experimental Accuracy Analysis (Microwave only) –Herbst et al., 1984 –Anderson et al., 1991, 1992 Fit v t =0,1,2 (torsional problem not well constrained) –Focused on a R branches some b-types –Analysis couldn’t handle many b-types  v t =0 K=9/v t =1 K=5 A,  v t =1 K=6,7,8

4 Molecular Spectroscopy Symposium June 2011 Methanol: A Perturbed History (3/3) Methanol Atlas used Ritz method/Power series –Did not go through strong perturbations –Did not fit lines Global analysis Xu & Hougen 1995, Mekhtiev et al –Included IR data mostly v t =0,1 TuFIR measurements of torsional transitions with microwave accuracy –E.g. Matsushima et al., 1994 & Odashima et al, 1995 Most recent analysis Xu et al v t =0,1,2 –Limited v t =2 data, no higher K values than in the Atlas

5 Molecular Spectroscopy Symposium June 2011 What remains to be solved Latest “global” analysis v t =0,1,2 Xu et al., 2008, JMS –V t =0 is good to J=30, K=13 –V t =1 is good to J=30, K=12 –V t =2 is good where levels were connected (otherwise serious problems) –No attempt at higher states Microwave a R branch and some TuFIR data on v t =3 Extensive IR data on v t =3, v t =4, CO stretch and CH 3 in-plane rock Some microwave data (and heterodyne laser data) on CO stretch and CH 3 rock Best CO stretch analysis is RMS of ~1cm -1 ! –Nasty physics involving coupling small and large amplitude vibrations –Problem not really solved

6 Molecular Spectroscopy Symposium June 2011 Why We Are Not Done Yet We observe J=35+ of these Q branches Source size from interferometery 1”x5” (Herschel is beam diluted badly!) 300K laboratory spectrum bottom Orion Top showing a v t =2 K=4-3 A-state Q-branch A component of methanol is >300K and ALMA will resolve it!

7 Molecular Spectroscopy Symposium June 2011 Experimental The direct multiplication spectrometer at JPL was utilized for most measurements Multiplication factors up to 162 were utilized (2.75 THz!!!) Transitions GHz were measured at OSU Millitech AMC-10

8 Molecular Spectroscopy Symposium June 2011 Data Previous microwave GHz, , , , New data –JPL , , , lamb-dips 300 GHz  Improved some poorer previous regions as well –OSU , New IR Lees et al., 2011, JSQRT in press –A few higher K levels in v t =0,1,2,3 and many new levels in v t =4

9 Molecular Spectroscopy Symposium June 2011 Comparison of Calculation to Measurements 1/2 V t = ± ± V t = V t = V t =

10 Molecular Spectroscopy Symposium June 2011 Comparison of Calculation to Measurements 2/2 V t = V t = V t = V t = V t = / /+ V t = – V t = V t = V t = / /+ V t = – V t = / /-

11 Molecular Spectroscopy Symposium June 2011 Comparison of Techniques Blue is Bruker 120, Orange (larger noise) is laser sideband, red multiplier

12 Molecular Spectroscopy Symposium June 2011 Connected Levels A-states Microwave accuracy connection in Xu et al., 2008 New microwave accuracy connection Existing microwave accuracy v t =3 connection Microwave accuracy connection not included in Xu et al IR data from Atlas No IR data IR data Lees et al. 2011

13 Molecular Spectroscopy Symposium June 2011 Connected Levels E-states

14 Molecular Spectroscopy Symposium June 2011 Key Problems Identified Transition between hindered and free rotor is still problematic to RAM Hamiltonian –All the v t =2 data is critical in making the transition to free rotor –Cusp levels A-state K=13, E-state K=8 are especially important Microwave data on v t =0,1,2 interacting triplets need to be included –Interaction appears to be fitting distortion now Higher K levels in v t =0 and 1 need to be identified in IR spectrum –Generally above 2.7 THz –Helps break correlation between K dependent distortion and torsion

15 Molecular Spectroscopy Symposium June 2011 Next Steps for Methanol Step 1: New Global analysis of v t =0,1,2 –Include all the IR data –Identify & include higher K v t =0, 1 transitions Step 2: Extend to v t =3 –Predict v t =3 and compare to existing data –Identify levels that are not pertubed in v t =3 –Expand analysis to “well behaved” v t =3 levels –Understand how RAM extrapolates in torsional state Step:3 Start solving the CO stretch, CH 3 in-plane rock region –Extract the microwave data to J=35 or so from existing spectra –Use deviations from ground torsional manifold as a guide to perturbations ALMA will get better spectra that we have in the laboratory so there is still work to be done

16 Molecular Spectroscopy Symposium June 2011 Conclusions Many High J and High K lines have been identified in the methanol spectrum Many new microwave accuracy connections have been made –Between torsional states –Between K sub-bands Sub-bands involving v t =2 – v t =3 cusp levels have been identified Sub-bands involving the A-state v t =0,1,2 K=15,13,11 identified Sub-bands involving two E-state v t =0,1,2 triplets have also been identified Many v t =3 bands have also been identified Overcoming the next two perturbations in the spectrum of methanol should be possible now. The RAM Hamiltonian extrapolates well in rotational constants The RAM Hamiltonian extrapolates less well in K The RAM Hamiltonian extrapolates poorly into the free rotor limit from the hindered limit

17 Molecular Spectroscopy Symposium June 2011 Acknowledgements This research was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. NASA Astrophysics Research and Analysis Program support and NASA support for Herschel Heterodyne Instrument for Far Infrared guaranteed time holders is gratefully acknowledged. © 2011 California Institute of Technology all rights reserved