molecular spectroscopy symposium 2013 17-21 june 2013 identification and assignment of the first...

Molecular Spectroscopy Symposium 2013 17-21 June 2013

Identification and Assignment of the First Excited Torsional State of CH2DOH

Within the o2, e2 and o3 Torsional Levels

John C. PEARSON, Shanshan YUJohn C. PEARSON, Shanshan YUJet Propulsion Laboratory, California Institute of TechnologyJet Propulsion Laboratory, California Institute of Technology

Laurent H. COUDERT Laurent H. COUDERT LISA, CNRS/Universités Paris Est et Paris Diderot LISA, CNRS/Universités Paris Est et Paris Diderot

L. MARGULÈS, R.A. MOTIYENKOL. MARGULÈS, R.A. MOTIYENKOLaboratoire PhLAM, Université des Sciences et Technologies de Laboratoire PhLAM, Université des Sciences et Technologies de

LilleLilleS. KLEE, S. KLEE,

Physikalisch-Chemisches Institut, Justus-Liebig-UniversitätPhysikalisch-Chemisches Institut, Justus-Liebig-Universität

2Molecular Spectroscopy Symposium 2013 17-21 June 2013

MotivationMotivation

Theory of Asymmetric-Top Asymmetric-Frame internal rotation is in its infancy– Three ground state examples HCOOCH2D, CH3CH2OH, CH2DOH all that exists– CH2DOH has large effects and a comprehensive IR and MW data set

CH2DOH was first discovered in the ISM by Jacq et al., 1993, A&A 271, 276CH3OH is often optically pumped (Far infrared thermal dust emission pumps the torsional bands)– CH2DOH should also be similarly excited

Issues remain in the abundance of CH2DOH relative to CH3OD– CH2DOH is greatly enriched after cold processing– CH3OD is equally abundant to CH2DOH in Orion KL!

Quasi-liquid phase on evaporating grains??? Something we don’t know (i.e. partitioning wrong due to pumping?)


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, vt=1 o2, e2 and o3

e to e a-type or b-type o to o a-type or b-typee to o c-type or x-type ( x is Ka=even & Kc=even) o to e c-type or x-type ( x is Ka=even & Kc=even) All are observed; e0-e1 a-types are weak and the x-types generally require mixing

OC

HHH

D

Symmetry and Selection RulesSymmetry and Selection Rules


SpectroscopySpectroscopy

Last year we reported the ground state (Pearson, Yu & Drouin, J. Mol. Spectrosc. 280, 119 (2012).– Term values to e0 Ka=10, e1 Ka=9 and o1 Ka=9 determined– aR branches to Ka=11 identified for all states– Nearly complete spectrum 60- 1200 GHz

Last year we also reported identification and assignment of 76 torsional sub-bands (El Hilali, Coudert, Konov, & Klee, J. Chem. Phys. 135, 194309 (2011).– Complete Far-IR 30-800 cm-1 spectrum

The combination of calculated band origins, some assigned Q-branches, and microwave accuracy ground state term values provided a basis for assignments– Torsion effects much large in excited states so THz spectra needed


New DataNew Data

Microwave Spectra recorded in 1310-1425, 1425-1600, 1600-1800, 1760-2010 & 2450-2700 GHz regions at JPL & Lots of unassigned lines in previous data

o1 K=11 to e1 K=10 Q


AssignmentsAssignments

Boot-strap assignments of ground state– Identified Q-branches connecting ground state to e0 K=14, e1 K=13 and o1 K=13– Confirmed previous aR-branch assignments– Identified aR-branches to e0 K=14, e1 K=13 and o1 K=13– Checked assignments with multiple loops from other Q branches

6 Q branches are possible for each Ka value in each state– Only issue identified is weak perturbation in e1 K=12 @ J=20

Fit all the new bands with power series model– B*J(J+1)-D*[J(J+1)]2+H*[J(J+1)]4+….– e1 K=12 fit with 4 J’s weighted out

Unidentified strong lines are excited torsional states!– Many Q-branches were easily located– P/R branches on series of very strong lines


Ground-State Torsional StructureGround-State Torsional Structure

There is a real difference in e1/o1 relative to e0

(B+C)/2 is significantly smaller in e1/o1

A is slightly smaller in e1/o1


Microwave Assigned BandMicrowave Assigned Band

K=0 K=1 K=2 K=3 K=4 K=5 K=6 K=7 K=8 K=9 o2

e2

o32253

1706

47

aR branch assigned and confirmed

aR branch assignment only

not assigned

P, Q and/or R in spectrumNumber is calculated Q origin

Branch confirmed with loops


IR Bands AssignedIR Bands Assigned

K=0 K=1 K=2 K=3 K=4 K=5 K=6 K=7 K=8 K=9

o2

e2

o3

e0

e1

o1


vvtt=1 Structure=1 Structure

Internal rotation is still hindered especially in o2, but becomes nearly free rotor thereafter


Interaction of oInteraction of o22 K=0 and K=2 K=0 and K=2

o2 Ka=2 Kc=J-1o2 Ka=0 or 2, Kc=J or J-2

o2 K=1

e2 K=0

Ka=0, Kc=J is completely mixed with Ka=2 Kc=J-2 due to asymmetryExtra bands are observed in all cases, asymmetry splitting is enormous


The 4-state interaction The 4-state interaction oo33 K=3, o K=3, o33 K=2, e K=2, e22 K=4 & o K=4 & o33 K=1 K=1

K=2 of o3 remains unconnected. It will reside between e2 K=4 and o3 K=3. There will be a Dab interaction with o3 K=3. No crossing to J=23


ee22 K=8 and e K=8 and e11 K=12 K=12

Interaction has x-symmetry (Ka=4,Kc=4) and is very weak (d1= 8.4622(59) x10-4 MHz fits the data)Probably only allowed due to mixing {i.e. a-type Coriolis between o1 and e1 (0,1) and a-type Coriolis between e2 and o1 (4,3/5)}


Future WorkFuture Work

Finish IR assignments connecting e0, e1, o1, o2, e2, and o3

Connect o3 K=2 to the rest of the levels (3 possible bands)– More will be allowed by mixing

Assign higher Ka values in o2, e2 and o3

Add IR bands involving e3, e4 and o4

– Identify aR-branches confirming assignments with loops– Identify microwave P,Q, & R branch connections– Understand why o3 K=8 is asymmetry

Add IR bands involving o5, e5, o6 and e6

– Identify aR-branches confirming assignments with loopsAssign the rest of the IR spectrum


Acknowledgements

Support for part of 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."

Part of this work was performed at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration

molecular spectroscopy symposium 2013 17-21 june 2013 identification and assignment of the first...

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