3-D SUBMILLIMETER SPECTROCOPY OF
ASTRONOMICAL ‘WEEDS’ – CONTINUED
ANALYSIS
SARAH M. FORTMAN, IVAN R. MEDVEDEV, CHRISTOPHER F. NEESE,
and FRANK C. DE LUCIA, Department of Physics,
The Ohio State University, Columbus, OH 43210, USA.
OSU International Symposium on Molecular Spectroscopy
Columbus, OH
June 22th, 2011
Introduction


Latest results for vinyl cyanide

Line list of 2895 lines

Point by point Fit of 2.4 million points
Comparison with an astronomical spectrum

Convolved the point by point fit to simulate line shapes

Fit the convolution to the astronomical spectrum
Vinyl Cyanide in the 210-270 GHz Region

445 scans with temperatures ranging from 236-386 K

Pressure ~.5 mtorr

192 assigned reference lines were used to calculate 𝑇 and

Pressure broadening correction (1 + ) where 𝑘 = −60583 MHz

618 of the strongest 2895 lines are in the current catalogs
𝑘
𝜈
𝑛𝐿
𝑄
Fitting Peaks and 1/T fits
Apeak
nL 8 3

(1  e h  / kT ) Sij  2 e  El / kT
Q 3ch
ln( 2 )



El
A
2
ln( Sij  ) 
 ln  peak

nL 8 3
kT
(1  e h  / kT )

Q 3ch


Fit each line in each scan to a
Gaussian lineshape to determine peak
amplitude

Fit the peak amplitude for each line as
a function of temperature to calculate
the strength parameter 𝑆𝑖𝑗 𝜇 2 and lower
state energy 𝐸ℓ

 
ln(2 )




 
 
Vinyl Cyanide Catalog

Tabularize the strength parameter and
lower state energy to create a catalog

Error codes tag blended, overlapping or
weak lines

Weak lines may be unnecessarily
tagged
All Lines
Error Codes

W = Width; the width of the line is
smaller or larger than expected

G = Gaussian; a number of Gaussian
fits returned unphysical results

T = Temperature; the 1/T is
unphysical
Tagged Lines
Frequency Shifts in Vinyl Cyanide

Negligible frequency shifts in the ground
state (black) and 11 excited state (red)

Significant shifts in the 15 excited state
(blue)

Green circles represent unexpected
intensities and indicate blending
New Point by Point Fitting Strategy

C2 

1  e T

Absorbance( )
 C1  M 
nL
T
Q


 ~ C3  E~
 Se T
nm 2 K1/2
C1  54.5953
amu 1/2D 2
K
C2  4.799237 10-5
MHz
K
C3  1.43877506
cm -1
Comparison to Astronomical Spectra
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Molecules in the Astronomical Spectrum
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Convolution Functions

Selected isolated lines and adjusted for the Doppler width and
scaled the amplitude to 1

Fit for the line shape

Number of lines fit ranged from 7 for MeCN to 47 for MeOH
Comparison of Five Molecules
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Comparison of Five Molecules
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Comparison of Five Molecules
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Fitting to the Astronomical Spectrum

Fit our convolved spectrum to the astronomical spectrum

Only free variable was concentration

Several unassigned features are modeled by the simulation
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Fitting to the Astronomical Spectrum
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Fitting to the Astronomical Spectrum
Astrophysical data from IRAM,
courtesy of Jose Cernicharo and
Belen Tercero
Conclusion


Results for vinyl cyanide in the 210-270 GHz Region

Line list of 2895 lines with frequency, strength parameter
and lower state energy

Point by point predictions which can used to predict a
spectrum at an arbitrary temperature
Comparison to an astronomical spectrum

Fits of the experimental predictions to the astronomical
spectrum yield good results
This work was supported by NASA Headquarters under the
NASA Earth and Space Science Fellowship Program - Grant
NNX09AP10H