developments in fast scan submillimeter spectroscopic technique (fassst) and computer aided...
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DEVELOPMENTS IN FAST SCAN SUBMILLIMETER SPECTROSCOPIC
TECHNIQUE (FASSST) AND
COMPUTER AIDED ASSIGNMENT OF ASYMMETRIC ROTOR SPECTRA (CAAARS)
SOFTWARE SUITE.
IVAN R. MEDVEDEV, FRANK C. DE LUCIA, AND PAUL HELMINGER
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
Sign
al c
hann
el
BWO
Magnet
Lens
Filament voltagepower supply
Length ~60 cm
Steppermotor
Reference channel
Lens
Stainless steel rails
Path of microwaveradiation
Preamplifier Freq
uenc
y ro
ll-off
prea
mpl
ifier
Referencegas cell
Glass rings used to suppress reflections
Data acquisition system
Computer
FAst Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer
5
4
3
2
(n=
n-1
)/10
-6
380370360350340330320310Frequency/GHz
0.4
0.2
0.0
-0.2
/M
Hz
380370360350340330320310Frequency/GHz
a) b) c)
Effect of atmospheric dispersion on frequency calibration accuracy
Strategy to overcome atmospheric absorption at higher frequency
-Purging of FP cavity reduces the effect of atmospheric absorption
-Higher frequency BWO oscillator tubeare less well behaved
InSb detector 1
InSb detector 2
Ring cavity: L~15 m
Mylar beam splitter 1
Mylar beam splitter 2
Aluminum cell: length 6 m; diameter 15 cm
BWO
Magnet
LensLength ~60 cm
Steppermotor
Lens
Stainless steel rails
Path of microwaveradiation
Referencegas cell
Glass rings used to suppress reflections
FAst Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer
Experimental Signal/Noise Ratio of ~1000 allows us to resolve transitions with energies ~1500 cm-1 above ground state.
Line shape and sensitivity
COMPUTER AIDED ASSIGNMENT OF ASYMMETRIC ROTOR SPECTRA (CAAARS)
SOFTWARE SUITE.
i. CAAARS is flexible software package designed for assignment of ro-vibrational molecular spectra.
ii. Point and click approach to line assignmentiii. The flexible sorting principle makes CAAARS applicable to a wide
range of spectroscopic problems iv. The organization of the predicted and assigned lines into branches
allows the user to plot easily Fortrat diagrams, intensity plots, R- or P-branch clusters, (Ka or Kc vs. frequency for a given J), errors, reduced energy plots, perturbed branch behavior, and whatever else is found useful for a given spectrum.
v. Compatible with SPFIT/SPCAT as well as ERHAM (Peter Groner)vi. Latest version requires Igor Pro version 6 software package for
operationvii. Available for downloading from
http://www.physics.ohio-state.edu/~medvedev/caaars.htm
Conclusions
i. Spectral coverage of the FASSST spectrometer has been extended to frequencies surpassing 1 THz
ii. Optical cavity employed by the spectrometer for frequency calibration now can be reliably purged with dry N2
iii. Absorption cell of the FASSST spectrometer can now be uniformly cooled and heated to a wide range of temperatures
iv. CAAARS software package has been further tested and improved. The latest release is available for downloading at
http://www.physics.ohio-state.edu/~medvedev/caaars.htm