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

260 GHz 375GHz

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

THz spectrum of Nitric Acid

Experimental Signal/Noise Ratio of ~1000 allows us to resolve transitions with energies ~1500 cm-1 above ground state.

Line shape and sensitivity

Heating and Cooling Capabilities of the FASSST spectrometer

MH08 - SARAH M. FORTMAN

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

CAAARS user interfaceemploying Fortrat diagram

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