Transcript Columbus13CH2DOH.ppt

Identification and Assignment of the First
Excited Torsional State of CH2DOH Within
the o2, e2 and o3 Torsional Levels
John C. PEARSON, Shanshan YU
Jet Propulsion Laboratory, California Institute of Technology
Laurent H. COUDERT
LISA, CNRS/Universités Paris Est et Paris Diderot
L. MARGULÈS, R.A. MOTIYENKO
Laboratoire PhLAM, Université des Sciences et Technologies de
Lille
S. KLEE,
Physikalisch-Chemisches Institut, Justus-Liebig-Universität
Molecular Spectroscopy Symposium 2013
17-21 June 2013
Motivation
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, 276
CH3OH 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?)
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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,
vt=1 o2, e2 and o3
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 mixing
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Spectroscopy
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 subbands (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
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New 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
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Assignments
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
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Ground-State Torsional Structure
Ground State Energy Differences at J=K
16
Energy Difference cm-1
14
12
10
e0 reduced
8
e1 reduced
6
o1 reduced
4
2
0
0
2
4
6
8
K Quantum number
10
12
14
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
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Microwave Assigned Band
47
o3
e2
o2
K=0
2253
1706
K=1
K=2
K=3
K=4
K=5
K=6
K=7
K=8
K=9
P, Q and/or R in spectrum
Number is calculated Q origin
aR branch assigned and confirmed
aR branch assignment only
Branch confirmed with loops
not assigned
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IR Bands Assigned
o3
e2
o2
o1
e1
e0
K=0
K=1
K=2
Molecular Spectroscopy Symposium 2013
K=3
K=4
K=5
9
K=6
K=7
K=8
K=9
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vt=1 Structure
J independend Band Origins
vt=1 Band Origins Relative to e0
290
450
270
400
260
250
240
o2
230
e2
220
o3
210
200
Energy cm-1
Energy origin cm-1
280
350
o2
300
e2
o3
250
200
190
0
0
2
4
6
Axis Title
8
10
2
4
6
K Quantum Number
8
10
Internal rotation is still hindered especially in o2, but becomes nearly free
rotor thereafter
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Interaction of o2 K=0 and K=2
214
o2 K=0
o2 K=1 lower
o2 K=1 upper
212
o2 K=2 lower
o2 K=2 upper
e2 K=0
210
o2 K=3 lower
o2 K=3 upper
208
o2 Ka=0 or 2, Kc=J or J-2
o2 K=4 lower
o2 Ka=2 Kc=J-1
o2 K=4 upper
o2 K=5 lower
206
o2 K=5 upper
o2 K=6 lower
204
o2 K=6 upper
o2 K=1
o2 K=7
202
o2 K=8
o2 K=9
e2 K=0
200
0
5
10
15
20
25
Ka=0, Kc=J is completely mixed with Ka=2 Kc=J-2 due to asymmetry
Extra bands are observed in all cases, asymmetry splitting is enormous
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The 4-state interaction
o3 K=3, o3 K=2, e2 K=4 & o3 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
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e2 K=8 and e1 K=12
Interaction has x-symmetry (DKa=4,DKc=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)}
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Future 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 loops
Assign the rest of the IR spectrum
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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
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