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ASSIGNMENTS, PERTURBATIONS, PATHOLOGIES AND A ROTATIONAL ANALYSIS OF THE SPECTRUM OF CH2DOH John C. PEARSON, Shanshan YU and Brian J. DROUIN Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr, Pasadena, CA 91109 Molecular Spectroscopy Symposium 2012 18-22 June 2012 Why CH2DOH When CH3OH Is Hard Enough? CH2DOH was first discovered in the ISM by Jacq et al., 1993, A&A 271, 276 Methanol in the ISM is known to be made on grains – Gas phase chemistry cannot reproduce observed abundance (Geppert et al., 2006, Faraday Discuss 133, 177) On grain surface D is efficiently incorporated in the Methyl group (Nagaoka et al., 2005, ApJ 624, L29 & Nagaoka et al., 2007, J. Phys. Chem. A 111, 3016) – Cold ISM conditions makes CH2DOH, CD2HOH and CD3OH (Parise et al., 2002, A&A 393, L49 & Parise et al., 2004, A&A 416, 159) – CD3OH was observed to be ~1% of methanol column in IRAS 16293 (Parise et al., 2004, A&A 416,159) CH2DOH is potentially an excellent tracer of star formation history and cold ISM material processing (Parise et al., 2006, A&A 453, 949) – It is believed that D enriched species on grain surface evaporate first once star formation starts Molecular Spectroscopy Symposium 2012 2 18-22 June 2012 Symmetry and Selection Rules D C O H H H Cs symmetry; All wave functions are even (A’ or e) or odd (A” or o) Torsion characterized by number of nodes; Ground state e0, e1 and o1 e to e a-type or b-type o to o a-type or b-type e to o c-type or x-type (x is DKa=even & DKc=even) o to e c-type or x-type (x is DKa=even & DKc=even) All are observed; e0-e1 a-types are weak and the x-types generally require some mixing Molecular Spectroscopy Symposium 2012 3 18-22 June 2012 C3V to CS Torsional Wave Functions All torsional states interact, resulting in avoided crossing within each torsional state grouping as well as between each torsional grouping Ordering for a given K is e0, e1 and o1 in increasing energy (applies to excited states as well) Molecular Spectroscopy Symposium 2012 4 18-22 June 2012 a-Type R-branches Unlike other highly prolate asymmetric top molecules the atype R-branch spectrum does not show the classic band head pattern due to torsional modulation The e0 state is well above the e1/o1 pair The o2/e2 and o3 states are lower in frequency # is Ka of J=13-12, Blue is e0, Red e1, and Green o1 Molecular Spectroscopy Symposium 2012 5 18-22 June 2012 Ground State Analysis 8356 Transitions were analyzed – Closed loops were performed All aR branches and DKa=1 transitions – Each K was fit to a power series (2x2) used for perturbations Analyzed a-type, b-type within each state, b-type and c-type between states Low Ka values were problematic, satisfactory for Ka>3 Reduced RMS 2.85 with a rejection criteria of 10 times experimental error – Constant r empirical analysis Fit all data to reduced RMS of 6.0 Reduced RMS was 2.49 if 344 high J lines were rejected – Term values to e0 Ka=10, e1 Ka=9 and o1 Ka=9 determined – aR branches to Ka=11 identified for all states Molecular Spectroscopy Symposium 2012 6 18-22 June 2012 “IAM” Hamiltonian Hamiltonian matrix showing the lowest order terms used in the analysis Molecular Spectroscopy Symposium 2012 7 18-22 June 2012 Spectral Pathologies: Low Ka Levels I Molecular Spectroscopy Symposium 2012 8 18-22 June 2012 Spectral Pathologies: Low Ka Levels II Molecular Spectroscopy Symposium 2012 9 18-22 June 2012 Torsion Effects vs. Theory [56] I. Mukhopadhyay, Spectrochimica Acta A 53, (1997) 1947 [58] A. El Hilali, L.H. Coudert, I. Konov, S. Klee, J. Chem. Phys. 135, (2011) 194309 The e0 state appears to be more localized than theory predicts Molecular Spectroscopy Symposium 2012 10 18-22 June 2012 Torsion o1-e1 vs Ethyl Alcohol Energy difference between o1 and e1 in CH2DOH (left) and Ethanol (right). The avoided crossing between the e1 and o1 states at K=0 does not represent the average splitting. Molecular Spectroscopy Symposium 2012 11 18-22 June 2012 Excited Torsional States aR branch of excited torsional states – o2 aR-branches Ka=0-7 assigned – o2 b-types Ka=1-0 and 2-1 – e2 aR-branches Ka=0,1,2,3,4?,5,7 – o2 Ka=3 e2 to Ka=2; o2 Ka=4 to e2 K=3 – o3 aR-branches Ka=0,1,2?,4-7 – o3 Ka=4 – o3 Ka=5 – e3 aR-branches Ka=0-3, 4 – o4 aR branches Ka=1, Kc=J-1 Many unassigned series – aR branches Ka=0,1 – 5 unassigned microwave Q-branches Molecular Spectroscopy Symposium 2012 12 18-22 June 2012 Excited Torsional State Energy Origins Avoided crossings of the torsional wave functions can be seen on the left Levels that are expected to interact are shown on the right with red arrows Molecular Spectroscopy Symposium 2012 13 18-22 June 2012 The o2 K=0 & 2 levels In the o2 state Ka=0 and Ka=2 are nearly degenerate due to the torsion – Energy difference between these states is 5457.8(1) MHz The asymmetry, B-C, connects J(0,J) and J(2,J-2) – Even though CH2DOH is nearly symmetric, asymmetry splitting in o2 K=2 is gigantic – The J=3-2 aR branch is 133688.327 and 134733.966 MHz – The e0 state is 134112.435 and 134185.476 MHz and has the largest B-C – The a-type DKa=2, DKc=1 R-branch was identified – The Ka=2-1 Q branch to J=25 and J=34 was identified confirming assignments Molecular Spectroscopy Symposium 2012 14 18-22 June 2012 Acknowledgements Support for this work, part of the NASA Herschel Science Center Theoretical Research/Laboratory Astrophysics Program, was provided by NASA through a contract issued by the Jet Propulsion Laboratory, California Institute of Technology under a contract with NASA. This work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration Thanks to Frank De Lucia and Rebecca Harlan for FASSST surveys taken at OSU Thanks to Richard Suenram for his Stark data. Thanks to Stephen Kukolich for use of his FTMW system Thanks to Herb Pickett for numerous useful discussion on internal rotation Molecular Spectroscopy Symposium 2012 15 18-22 June 2012