1. Acetaldehyde: Into the Submillimeter
Brian J. Drouin, Herbert M. Pickett
California Institute of Technology,
Jet Propulsion Laboratory
Pasadena, CA

2. Outline
Motivation
Previous Work
New Data
Current Fit
Future Plans

3. Motivation Astronomy Spectroscopy Chemistry Highly abundant in ISM
Bright and messy (weed or flower?)
Spectroscopy
Strong theoretical background
Test case for low-barrier fitting routines
Improve IAMCALC/SPFIT
Chemistry
Look for geminol?

4. Previous Work
A. Bauder, F. J. Lovas, and D. R. Johnson, 1976, J. Phys. Chem. Ref. Data, 5, 53. (vT = 0)
I. Kleiner, M. Godefroid, M. Herman, and A. R. W. McKellar, J. Mol. Spectrosc. 142, 238, 253 (1990) (vT = 1  0)
I. Kleiner, J. T. Hougen, R. D. Suenram, F. J. Lovas, and M. Godefroid, J. Mol. Spectrosc. 148, (1991). (vT = 0, FT fix)
I. Kleiner, J. T. Hougen, R. D. Suenram, F. J. Lovas, and M Godefroid, J. Mol. Spectrosc. 153, (1992). (vT = 0,1 global)
W. L. Barclay, Jr., M. A. Anderson, L. M. Ziurys, I. Kleiner, and J. T. Hougen, Astrophys. J. Suppl. 89, (1993). (vT = 0,1;< 325 GHz) 
S. P. Belov, M. Yu. Tretyakov, I. Kleiner, and J. T. Hougen, J. Mol. Spectrosc. 160, (1993). (vT = 2)

5. The back-story Original MW was ugly FIR spectrum FTMW
Typical for an asymmetric internal rotor though
Barrier and structure good
FIR spectrum
Minimal assignments due to congestion
Assignments inconsistent with MW
FTMW
New assignments – global fit possible

6. SPFIT Then and Now
Then
JPL catalog entry A. Bauder, F. J. Lovas, and D. R. Johnson, 1976,
J. Phys. Chem. Ref. Data, 5, 53.
A state - Asymmetric top rigid rotor
E State - Pa, PaP2, PaP4, Pa3, Pa3P2, and Pa5 terms. The fit produced
observed--calculated frequencies that were 3.5 times the experimental uncertainties
in an RMS sense.
Now
Internal Axis Method ‘front end’ IAMCALC
Set up A and E states for 3,6,9… “vibrational states” to form torsional basis
Generate Fourier terms from Mathieu function – big ‘par’ file
Run SPFIT/SPCAT as usual
Iterate through IAMCALC as necessary
Start with Kleiner’s vT = 0,1,2 assignments – verify and improve with new data

7. Theory
Phenomenological periodic solutions to Mathieu Equation for one ‘vibration’
‘Global’ analyses using torsional basis set

8. The “IAM” file Define r, n, Max M, Max v = 3*max vT Max series Flags:
/ V3
/ V6
/ F
/-2*k7
/-2*k7
/-2*F*rho
/ Lv
/ k1
/ c4
/ del_ab
E-06 / lv
E-03 / lamv
E-03 / lk
E-06 / c4J
E-03 / c10
/ k3
E-06 / k3J
E-03 / k3K
E-03 / c12
E-03 /del_ab3
/ ??
/ A-(B+C)/2
/ (B+C)/2
/ (B-C)/4
/ Dab
/ -Fv
/ -Fv
/-k5
/-k5
/-c2/2
/-c2/2
/-dab
/-dab
/-K2
/-K2
E-03 /-DJ
/-DJK
/-DK
E-03 /-fv
E-03 /-fv
E-03 /-k5J
E-03 /-k5J
/-fk
/-fk
E-03 /-dJ
/-dK
/ DabJ
/ DabK
E-06 / DabJJ
E-06 / DabJK
E-03 / DabKK
E-09 / HJ
E-06 / HJK
E-03 / HKJ
E-03 / HK
E-06 / hJK
E-06 / hK
/k6?
/ k4
E-03 / Mv
E-03 / c3
/ Gv
/ k2
/ c1
/ Del_ab
E-06 / gv
E-03 / k2J
E-03 / k2K
E-06 / c1J
E-03 /c3c
/ Dac
E-03 / c6
E-03 / c6
E-03 / c9
E-03 / c9
/ k6J
/ k7J or Ov
/ K4
/ c11
/ddab
E-03 / c22
E-03 / ??
/ ddel_ab
/ E+00 /mu_a
/ E+00 /mu_b
Define r, n,
Max M,
Max v = 3*max vT
Max series
Flags:
Choose type of series
++Fourier
- integer K
Parameters:
Commutators and
½ anticommutators

9. New Data 499 GHz 500 GHz 490 GHz 500 GHz 430 GHz 500 GHz

10. New Data
570 GHz GHz

11. New Data
770 GHz GHz

12. New Data
850 GHz GHz

13. New Data
g.s. rQ11
(simulation shifted 0.5 MHz from prediction based on current fit)
GHz GHz

14. New Data
g.s. rQ12 E A
1167 GHz GHz

15. Current Fit >3800 transitions (1200 previous from < 339 GHz)
Removed FIR (for now) and low res MW
Current fit is reduced rms 1.2
cm-1 FIR, 120 kHz MW
< 608 GHz assigned
J < 51, K < 21
1517 loops

16. Current Fit One iteration is 130 Seconds for 1.6 GHz system . rQ12
Assignments straightforward, fringe assignments are 300 kHz residuals
Slowly improve parameters and close loops

17. Future Plans Assign vT < 3 data through 1200 GHz
Achieve high quality analysis
Publish and update catalog

18. Acknowledgements NASA - Astrophysics R&A Herschel Lab Support
Kleiner code as verification for Hamiltonian

19. Multiplier Data & Collaborations
* manuscript submitted/accepted