Post on 21-Jan-2016
3-D SUBMILLIMETER SPECTROSCOPY FOR ASTROPHYSICS AND SPECTRAL
ASSIGNMENT
SARAH M. FORTMAN, IVAN R. MEDVEDEV, FRANK C. DE LUCIA, Department of Physics, The Ohio State University,
Columbus, OH 43210-1106, USA.
OSU International Symposium on Molecular Spectroscopy
Columbus, OH
June 16th, 2008
Two Related Objectives
Spectroscopy Challenge• Bootstrap Assignment in Complex Spectra• FASSST spectra may contain >10^5 lines in many
vibrational states
Traditional Approach• Use 2D (intensity, frequency) spectra to assign and
bootstrap in each vibrational state
New Approach• Observe intensity calibrated variable temperature
spectrum and calculate lower state energies.• Use intensity, frequency and lower state energies in
the bootstrap assignment
Astronomy Challenge• Current telescopes approach confusion limit• Many unassigned lines• New systems (Alma, Herschel) will be more
powerful
Traditional Approach• Quantum Mechanical predictions of astrophysical
spectra give intensity and frequency as a function of temperature
• Spectroscopists calculate and fit what we can, not what astronomers need
New Approach• Predict intensity and frequency as a function of
temperature without assignment
courtesy of J. Cernicharo
Intensity Calibrated Variable Temperature Spectroscopy• Observe 2D spectra at many temperatures• Calculate intensity, frequency and lower state
energies for assigned and unassigned lines• Give astronomers what they want• Give spectroscopists more information
FREQ ERR LGINT DR ELO GUP TAG QNFMT QN’ QN”222205.8884 0.0141 -7.0138 3 1502.8669 81 630061404402218 1 402119 1 222206.5102 0.0142 -7.0138 3 1502.8675 81 630061404402318 1 402219 1 222216.2472 0.0128 -6.1572 3 916.1480 21 63006140410 8 2 0 9 8 1 0 222222.2687 0.0241 -7.3542 3 1502.8669 81 630061404402318 1 402119 1 222662.1685 0.1481 -7.8356 3 2033.0142109 630061404543718 0 543619 0 222662.5968 0.0071 -6.0426 3 915.3357 21 63006140410 7 3 0 9 7 2 0 222665.1993 0.1573 -7.8356 3 2033.0133109 630061404543618 0 543519 0 222696.0695 0.0098 -6.7291 3 900.5161 17 630061404 8 6 2 0 7 4 3 0 222725.9166 0.1222 -7.8669 3 1956.8275105 630061404523319 1 523320 1 222746.5775 0.1175 -8.1094 3 1956.8268105 630061404523319 1 523220 1 222800.4652 0.1143 -8.1092 3 1956.8275105 630061404523419 1 523320 1 222821.1262 0.1312 -7.8664 3 1956.8268105 630061404523419 1 523220 1
Spectroscopic Challenge
NEW PARAMETER (EST. ERROR) 1 910099 1.468190000( 0) 0.000000000 2 0 26355017.840800( 0) 0.000000 3 10000 12962.3189(307) 0.0000 4 20000 12085.7215(308) -0.0000 5 30000 6242.05887( 35) 0.00000 6 610000 -196.061( 69) 0.000 7 610100 2.464( 33)E-03 -0.000E-03 8 611000 -2.3201(144)E-03 -0.0000E-03 9 610200 -0.0928( 48)E-06 -0.0000E-0610 612000 -0.06750(269)E-06 -0.00000E-0611 1000000000 -17.7136( 60) -0.0000 12 1000000100 -0.4134(150)E-03 0.0000E-03
Predicted lines from SPFIT .cat file Fitted Constants from SPFIT .fit file
Graphing in Two and Three Dimensions
Frequency (MHz)
Intensity
(nm2*MHz)
Lower State Energy (cm-1)
162977 5.1963711 631.1015
163119 17.025509 113.2438
163568 5.0442872 400.8251
163606 37.162086 65.264397
163925 4.3062572 488.5152
• Traditional approach uses a 2D (intensity vs. frequency) plot
• New approach creates a 3D plot from the intensity, frequency and lower state energy data
Interference fringes Spectrum
InSb detector 1
InSb detector 2
Ring cavity: L~15 m
Mylar beam splitter 1
Mylar beam splitter 2
High voltagepower supply
Slow wave structuresweeper
Aluminum cell: length 6 m; diameter 15 cm
Trigger channel /Triangular waveform channel
Sig
na
l ch
an
ne
l
BWO
Magnet
Lens
Filament voltagepower supply
Length ~60 cm
Steppermotor
Reference channel
Lens
Stainless steel rails
Path of microwaveradiation
Preamplifier
Fre
qu
en
cy
ro
ll-o
ffp
rea
mp
lifi
er
Referencegas cell
Glass rings used to suppress reflections
Data acquisition system
Computer
FAst Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer
Thermal enclosure
Temperature Control
• Ran experiment once• Temperature Range: 228 – 405 K (-45 – 132 °C) at ~.8 degrees/min• Took 700 scans over 3.5 hours totaling 29.6 GB of data
Spectra as a Function of Temperature
• The physical basis of the calculation of the lower state energy is the differential change in line strength with temperature.
Subset of Data
(in total experiment 700 traces over 50 GHz)
Ratios to Obtain Lower State Energy
kTEE uaeC /)(1
sgnsgn
0
/
/
,,
2
,
3/
sgnsgn
3
8)1 )( )(
sgn
sgn
n
kTEn
kTEl
zyxiuli
kThuu
n
u
u
eg
eg
che(TnT
0
/
/
,,
2
,
3/
sgnsgn
3
8)1 )( )(
sgn
sgn
n
kTEn
kTEl
zyxiuli
kThaa
n
a
a
eg
eg
che(TnT
kT
EEC
T
Tor ua
u
a )(]
)(
)(ln[ sgnsgn
2sgn
sgn
sgnsgn * au EkslopeE
We can plot the log of the ratio in log(1/T) space and expect to see a straight line.
• Scatter from the peak finder
• Ripples (variation in reflection with T?)
• Temperature calibration (currently thermocouples, starting to use spectroscopic temperature)
Consider taking the ratio of two lines of which one is assigned and the other is unassigned.
Lower State Energy vs. Thermal Behavior
Okay but not great
Astronomy
• The smallest errors in intensities will come when the calculated temperature is bounded by experimental temperatures
• The error in the predicted intensity will be of the order the error in the observations (or better because we make many observations).
Propagation of Error and Uncertainties
Spectroscopy
We expect to reduce uncertainties by a factor of 10 by:• Replacing the peak finder with analysis• Fitting a model to the baseline ripple• Using a grand fit of all assigned lines as the reference line
instead of a single line• Getting a proper average over the ends by using the
spectroscopic temperature• Operating over a larger temperature range (using a
collisional cooling cell to 2K)
221
213
223
31,
32,
31,
32,
)/1/1(
)/1/1()/1/1(2
)(
)(
)(
)(
TT
TTTT
T
T
T
T
ul
ul
ul
ul
ul
ul