Submillimeter-wave Spectroscopy of 13 C 1 -Methyl formate [H 13 COOCH 3 ] in the Ground State Atsuko Maeda, Ivan Medvedev, Eric Herbst, Frank C. De Lucia, Department of Physics, The Ohio State University, Columbus, OH and Peter Groner Department of Chemistry, University of Missouri- Kansas City, Kansas City, MO
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Submillimeter-wave Spectroscopy of 13 C 1 -Methyl formate [H 13 COOCH 3 ] in the Ground State Atsuko Maeda, Ivan Medvedev, Eric Herbst, Frank C. De Lucia,
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(Computer Aided Assignment of Asymmetric Rotor Spectra)
(1) Medvedev et al. J. Mol. Struct. 742, 299 (2005)
Spectrum of 13C1-Methyl formate
Transitions of 13C1-Methyl formate
Observed R-transitions, A-state
0
5
10
15
20
25
30
0 10 20 30 40 50 60
J
Ka
Previous
Present
1900 lines → 2200 A transitions2200 lines → 2300 E transitions
a, b-type R, Q, P transitions+
c-type R, Q & x-type R transitions
Observed Q-branch transitions, A-state
0
5
10
15
20
25
30
0 10 20 30 40 50 60
J
Ka
Previous
Present
Effective Rotational Hamiltonian (ErHam) by Groner
Peter Groner, J. Chem. Phys. 107, 4483 (1997)
• Developed for dual or single internal rotorsdimethyl-ether, 3-methyl-1,2-butadiene, aceton, ethyl methyl ether, dimethyl diselenide, methyl cabamate… etc.
• Principal axes system (PAS) or Rho axis system (RAS)
• Torsional energy, rotational constants are given as Fourier series
Effective Hamiltonianbased on principal axes system
Hrot forasymmetric rotor
Torsional energy
Coriolis interaction
negligible
where
Molecular Constants of 13C1-Methyl formate
Prediction for astronomical observation
53 parameters for A & E substates (~4800 lines) with RMS = 90 kHz
Comparable with Willaert et al. (2006)
Systematic Deviations at Low Ka
E substate
A substate
Perturbation at Ka = 0, 1 hardly happens
perturbation at high J / Ka affectsthrough least-square fitting
Q-branch transitions (Ka = 0, 1)
Perturbation at High Ka
-1
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1
0 10 20 30 40 50 60
Rotational Quantum Number J
Ob
s-C
alc
. /
MH
z
R branch transitionsin the A substate
Ka ≥ 15
Single state analysis of the A state with a rotational Hamiltonian for asymmetric-top rotors
Perturbation…?
• Perturbation partner
CH3 torsion (ν = 130 cm-1)
COC bending (ν = 318 cm-1)
CO torsion (ν = 332 cm-1)
• No Δv≠0 interaction in the ErHam
• Van Vleck transformation?
Too close to use
→→ interaction term directly0
100
200
300
400
500
600
0 5 10 15 20 25 30 35
J
En
erg
y le
vels
[cm
-1] Ka > ~15
Conclusions
• 3000 lines in 110-380 GHz were newly assigned to 4800 transitions of 13C1-methyl formate in the ground state.
• Most of transitions were fitted satisfactorily within 100 kHz.
• Perturbation from excited torsional states?
• Prediction of transition frequencies of 13C1-methyl formate has been made.
• The first excited torsional state of 13C1-methyl formate is now being investigated.