1. Spectroscopy of the ground, first and second excited torsional states of acetaldehyde from 0.05 to 1.6 THz. Ivan Smirnov a, Eugene Alekseev a, Vadim Ilyushin a Laurent Margules b, Roman Motiyenko b, Brian Drouin c a Institute of Radio Astronomy of NASU, Kharkov, Ukraine. b Laboratoire de Physique des Lasers, Atomes et Molécules, UMR 8523 CNRS-Université Lille 1, France c Jet Propulsion Laboratory, California Institute of Technology, USA

2. S. Muller, A. Beelen, M. Guelin, S. Aalto, J. H. Black, F. Combes, S. Curran, P. Theule, and S. Longmore,” Molecules at z = 0.89. A 4-mm-rest-frame absorption-line survey toward PKS 1830−211” Astron.Astrophys. 535, A103 (2011).

3. Previous work on the CH 3 CHO rotational spectrum First measurements – C.C.Lin, R.W. Kilb “Microwave Spectrum and Internal Barrier of Acetaldehyde” J. Chem. Phys. 24, 631 (1956). Subsequent work – about 20 publications The present work is based on the last two works: a)I. Kleiner, J. T. Hougen, J.-U. Grabow, S. P. Belov, M. Yu. Tretyakov, J. Cosléou “The Third and Fourth Torsional States of Acetaldehyde” Journal of Molecular Spectroscopy Vol. 179, p.41–60, 1996. b)I. Kleiner, N. Moazzen-Ahmadi, A.R.W. McKellar, T.A. Blake, R.L. Sams, S.W. Sharpe, G. Moruzzi, J.T. Hougen “Assignment, fit, and theoretical discussion of the 10 band of acetaldehyde near 509 cm -1 ” Journal of Molecular Spectroscopy 252 (2008) 214–229. Results in these  20 papers: maximum frequency - 417.2 GHz, rotational quantum number range: J  26 and K a  14.

4. Submillimeter wave and THz radio astronomy ALMA (31 – 950GHz) HERSCHEL (HIFI 490 – 1910 GHz) SOFIA (1400 – 1900 GHz) frequency, GHz 1 THz 2 THz T=100K I. Kleiner, F.J. Lovas, M. Godefroid, “Microwave Spectra of Molecules of Astrophysical Interest. XXIII. Acetaldehyde”, Journal of Chemical Physical Reference Data, Vol. 25, p.1113-2111, 1996. A = 56799.1 MHz B = 10162.2 MHz C = 9089.2 MHz

5. Our results IRA NASU (Ukraine): 49 – 149 GHZ PhLAM (France): 150–322, 400–533, 580 -660, 760-950 GHz JPL (USA): 950-1059.9 GHz, 1.060-1.205 THz, 1.576-1.626 THz 16126 newly measured lines + 3108 «old» = 19234 lines in the fit Rotational quantum number range J ≤ 66 and K a ≤ 22 Upper frequency 1.625 THz Rho axis method, 111 parameters (173 lines per parameter), weighted root mean square deviation is 0.68

6. 794750 795350795950MHz Prediction Experiment (2 nd harmonic detection) AE υ t = 0 41 6,35 ←40 6,34 υ t = 0, Q Ka = 9←8 (A) 3130292827262524232221201918 υ t = 0 Q Ka = 9←8 (E) 302928262524232221201927 Portion of the recorded spectrum of CH 3 CHO around 795 GHz.

7. 1 THz2 THz (1) (2) T=100K 1 THz2 THz (1) (2) T=300K Rotational spectrum of acetaldehyde in the 1 GHz – 3 THz frequency range (1) – a R 0,1 transitions (2) – b R 1,  1 transitions 14 14,1  13 13,0 14 14,0  13 13,1 31 0,32  30 0,31

8. Conclusions A new global study of the acetaldehyde (CH 3 CHO) spectrum in the wide frequency range up to 1.6 THz has been carried out and a fit within experimental error has been achieved for the lowest three torsional states of the molecule using the RAM approach. The range of rotational quantum numbers fitted in the current study covers all of the strongest transitions of interest for the modern submillimeter wave and THz radio astronomy.

9. Thank you for your attention