Transcript The Analysis of Acetonitrile 06172013a.pptx

The Analysis of Acetonitrile
(CH3CN) Using 3-D Submillimeter
Spectroscopy
JAMES P. MCMILLAN, SARAH M. FORTMAN, CHRISTOPHER F. NEESE, and FRANK C.
DE LUCIA
The 68th International Symposium on Molecular Spectroscopy
June 18, 2013
The Ohio State University
Motivations
Primary:
Understand the complete contribution of each
‘Weed’ to the astrophysical data
Methodology:
Intensity calibrated, temperature dependent approach to
spectroscopy
Bonus:
Obtaining line strength and lower state energies which may
aide in QM assignments
Motivations
ALMA Science Verification Data
Problems:
• Incomplete Catalogs
• Dense Spectra
Goal:
• Identify lines/features
of unknown origin
Fortman S. M. et al., J. Mol. Spectrosc. 280;11-20
Astrophysical Analysis
Steps:
Acetonitrile In The Orion KL Hot Core
1.) Generate a complete
temperature resolved
spectrum (CTRS)
2.) Convolve spectra with
astrophysical line shape
3.) Adjust for column
density
190K (LTE) CTRS of Acetonitrile
ALMA
Astrophysical Analysis
13CH
3CN
vs ALMA
Correcting for terrestrial and
interstellar isotopic abundances
Scaled for isotopic abundance
by a factor of 2.5
CH313CN & Terrestrial vs. ALMA
190K CTRS - 13C Acetonitrile
190K CTRS - Terrestrial Acetonitrile
ALMA
The 600-650 GHz Band
Complete Spectrum at 300K
Data Taken:
Temperature Range: 230-390 K
150 Spectral Averages
~1K per Spectral Average
Processing:
Spectroscopically determine number
density and temperature from Q.M.
catalogs
Fit data to acquire parameters to
generate CTRS at arbitrary temperatures
Result:
~1% intensity error in large lines
Returns lower state energies and line strengths
for each line
Complete Temperature Resolved Spectrum (CTRS)
Ground State
J = 35 ←34
𝜈8
CTRS vs Lab Spectra
J = 35 ←34
Result:
~1% intensity error in large lines
CTRS vs Lab Spectra
J = 35 ←34
Result:
~1% intensity error in large lines
Discrepancies With QM Catalog
J = 35 ←34 ;Ground State
Discrepancies With QM Catalog
Percent Residuals From Temperature Fit At 230K
Systematic errors in
temperature fit
Correlated with:
• Lower State Energy
• QM Number
• Intensity
QM catalog lines are used to spectroscopically determine the
temperature in the cell
Lower State Energies For ALL Lines
Displayed: Lines of S/N ≥ 3 at 300K
Lower State Energies For ALL Lines
Displayed: Lines of S/N ≥ 3 at 300K
Catalog lines removed
Lower State Energies For ALL Lines
Displayed: Lines of S/N ≥ 3 at 300K
Catalog lines removed
Lower State Energies For ALL Lines
2𝜈8
𝜈4
𝜈7
Displayed: Lines of S/N ≥ 3 at 300K
Catalog lines removed
3𝜈8
Summary
• Demonstrated the ability to generate a
complete spectrum at arbitrary temperatures
• Shown how this spectrum is useful to
astrophysical analysis
• Acquired lower state energies and line
strengths for all lines in a spectrum