Transcript Columbus12CH2DOH_f

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
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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
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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
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
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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)
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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
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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
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“IAM” Hamiltonian
Hamiltonian matrix showing
the lowest order terms used
in the analysis
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Spectral Pathologies: Low Ka Levels I
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Spectral Pathologies: Low Ka Levels II
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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
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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.
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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
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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
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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
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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
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