Submillimeterwave Spectroscopy of 13C1Methyl formate H13COOCH3 in the Ground State - PowerPoint PPT Presentation

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Submillimeterwave Spectroscopy of 13C1Methyl formate H13COOCH3 in the Ground State

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Eric Herbst, Frank C. De Lucia, Department of Physics, The Ohio State ... Department of Chemistry, University of Missouri-Kansas City, Kansas City, MO ... – PowerPoint PPT presentation

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Title: Submillimeterwave Spectroscopy of 13C1Methyl formate H13COOCH3 in the Ground State


1
Submillimeter-wave Spectroscopy of13C1-Methyl
formate H13COOCH3in 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

2
(Normal) Methyl formate
  • One of abundant interstellar molecules
  • in hot cores corinos (Orion KL, Sgr B2)

T 100-300 K
Ultra-compact HII region
O,B star
n 10(6)-10(8) cm-3
Cold background
Hot Core
3
CH3 Internal Rotationin Methyl formate
with ZPVE (zero-point vibrational correction)
E
407 MHz (0.0135 cm-1)
A
Senent, Villa, Meléndez and Dominguez-Gomez, ApJ.
627, 567 (2005)
4
Previous Rotational Studies of Methyl formate
  • Curl (1959) - HCOOCH3, DCOOCH3, HCOOCH2D,
    H13COOCH3, HCOO13CH3,
  • HC18OOCH3, HCO18OCH3 10-30 GHz vt 0 (A, E),
    HR
  • Bauer (1979) - HCOOCH3 5-58 GHz vt 0 (A, E),
    IAM
  • DeMaison et al. (1983) - HCOOCH3 220-240 GHz
    vt 0 (A, E)
  • Plummer et al. (1984) - HCOOCH3 140-550 GHz vt
    0 (A), HR
  • Plummer et al. (1986) - HCOOCH3 140-300 GHz vt
    0 (E), PAM
  • Oesterling et al. (1995) - DCOOCH3 -680 GHz vt
    0 (A, E), RAM
  • Oesterling et al. (1999) - HCOOCH3 -380 GHz vt
    0 (A, E), RAM
  • Karakawa et al. (2001) - HCOOCH3
  • Odashima et al. (2003) - HCOOCH3 7-200 GHz vt
    0 (A, E), 1 (A), IAM

Fewer studies for isotopologues
5
Previous Study of 13C1-Methyl formate
  • Willaert et al. (2006)
  • 7-62, 300-322 570-610 GHz
  • Ground A, E states
  • Jmax 58 (Kmax 24)
  • RAM Hamiltonian

13C
A few b-type transitions No prediction
Detection in interstellar media??
Willaert et al. J. Mol. Struct., 795, 4 (2006)
6
Experiment
  • FASSST spectrometer at OSU
  • 110-380 GHz with three BWOs
  • 100 scans accumulation
  • up down-ward sweeps ? averaged
  • SO2 lines ring cavity for frequency calibration
  • Commercial H13COOCH3
  • (Cambridge Isotope Laboratories, Inc.)
  • A few mTorr in 8 m-long aluminum cell
  • under room temperature

7
FASSST Spectrum of 13C1-Methyl formate
9000 lines with S/N gt 5
CAAARS(1) (Computer Aided Assignment of
Asymmetric Rotor Spectra)
(1) Medvedev et al. J. Mol. Struct. 742, 299
(2005)
8
Spectrum of 13C1-Methyl formate
9
Transitions of 13C1-Methyl formate
a, b-type R, Q, P transitions c-type R, Q
x-type R transitions
1900 lines ? 2200 A transitions 2200 lines ? 2300
E transitions
10
Effective Rotational Hamiltonian (ErHam) by
GronerPeter Groner, J. Chem. Phys. 107, 4483
(1997)
  • Developed for dual or single internal rotors
  • dimethyl-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

11
Effective Hamiltonianbased on principal axes
system
Hrot for asymmetric rotor
Coriolis interaction
negligible
Torsional energy
where
12
Molecular Constants of 13C1-Methyl formate
53 parameters for A E substates (4800 lines)
with RMS 90 kHz
Comparable with Willaert et al. (2006)
Prediction for astronomical observation
13
Systematic Deviations at Low Ka
Perturbation at Ka 0, 1 hardly
happens perturbation at high J / Ka
affects through least-square fitting
A substate
E substate
Q-branch transitions (Ka 0, 1)
14
Perturbation at High Ka
Single state analysis of the A state with a
rotational Hamiltonian for asymmetric-top rotors
R branch transitions in the A substate
15
Perturbation?
  • Perturbation partner
  • CH3 torsion (? 130 cm-1)
  • COC bending (? 318 cm-1)
  • CO torsion (? 332 cm-1)
  • No ?v?0 interaction in the ErHam
  • Van Vleck transformation?
  • Too close to use
  • ?? interaction term directly

Ka gt 15
16
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.
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