The Microwave Spectrum of Monodeuterated Acetamide CH 2 DC(=O)NH 2 I. A. Konov, a L. H. Coudert, b C. Gutle, b T. R. Huet, c L. Margulès, c R. A. Motiyenko, c H. Mollendal, d and J.-C. Gillemin e a Department of Physics, Tomsk State University, Tomsk, Russia b LISA, CNRS/Universités Paris Est et Paris Diderot, Créteil, France c PhLAM, CNRS/Université de Lille I, Villeneuve d’Ascq, France d CTCC, Dept. of Chemistry, University of Oslo, Oslo, Norway e ISCR, UMR 6226, Rennes, France

CH 2 DC(=O)NH 2 is of astrophysical relevance & theoretically interesting Normal species detected in Sagittarius B2(N) 1 Almost free internal rotation of its CH 2 D methyl group Oblate asymmetric top 1. Hollis, Lovas, Remijan, Jewell, Ilyushin, and Kleiner, Astr. J. 643 (2006) L25

Overview Hindering potential changes upon deuteration Torsional energy levels Available microwave data Tentative assignment & fit

The hindering potential of the normal species 1. Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Mol. Spec. 227 (2004) 115

Deuteration effects: potential energy function Upon deuteration the potential energy function remains an even function of α but no longer has 2π/3 periodicity, only 2π. V i ' coefficients are unknown.

Deuteration effects: potential energy function For deuterated methanol, 1 V 3i ' = V 3i, and 1. Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spec. 256 (2009) Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Mol. Spec. 227 (2004) 115 { V 1 ' = 9.95 cm -1 CH 2 D V 1 ' = cm -1 CD 2 H In the present case, 2 V 3 ' = , V 6 ' = , and V 1 ' = ± 10 cm -1

Deuteration effects: potential energy function V 1 = +10 cm -1 V 1 = -10 cm -1

Deuteration effects: torsional energy levels Normal species V 1 = 0 V 1 = -10 cm -1 V 1 = +10 cm -1 Quade and Suenram, J. Chem. Phys. 73 (1980) 1127

Torsion-rotation energy levels Torsion-rotation energies are calculated using the model developed for CH 2 DOH. 1 It depends on 8 kinetic energy parameters describing the 4x4 generalized intertia tensor, on 6 potential energy parameters V 1, V 2, V 3, …, and on distortion parameters. 1. Paper RF10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014)

Torsion-rotation energy levels Due to the fact that acetamide: Oblate asymmetric top Axis of internal rotation is // to the a-axis It is more difficult to understand torsion-rotation energy levels than in methanol. A J-dependence arises in addition to the K- dependence.

Torsion-rotation energy levels V 1 = +10 cm -1 e 0 torsional state: J 0,J J 1,J-1 J 2,J-2 J 3,J-3 J 4,J-4 V 1 = -10 cm -1 V 1 can be determined analyzing the microwave data

The microwave spectra 780 Stark Modulation Millimeter Wave Millimeter Wave Frequencies are in GHz Molecular Beam 3 room temperature spectra Cold temperature spectrum

The Stark modulation spectrum Line assignment will be an issue

First assignments 14 transitions were assigned in the cold spectrum. Their assignment in terms of rotational quantum numbers was performed with the help of the hyperfine structure. Due to the low temperature in the beam they were assigned to the e 0 torsional state.

Assignment problem When J increases, clusters of lines characterized by the same K c -value arise leading to many broadened transitions in the spectrum.

Assigning the room temperature spectra The 3 room temperature spectra were assigned using a bootstrap method with the Watson-type Hamiltonian. 305 transitions could be assigned up to J = 23 and K a = 10 for the e 0 torsional state. The RMS of 0.9 MHz. The fit degrades when K a increases.

Torsion-Rotation Hamiltonian fit 171 transitions with J ≤ 12 and K a ≤ 7 were fitted with the Torsion-Rotation Hamiltonian. 1 The RMS of the fit is 0.7 MHz and 21 parameters were determined. We did not try to go to higher J- or K a -values because we are not sure about the line assignment. Labeling the torsion-rotation levels arising from the Torsion-Rotation Hamiltonian was also a problem Paper RF10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014) Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Mol. Spec. 227 (2004) 115

Torsion-Rotation Hamiltonian fit a Constrained value

Torsion-Rotation Hamiltonian fit Deuteration effects are dominant.

Conclusion Assignment of the spectrum is an issue. We need to identify transitions involving o 1 and e 1.