The Microwave Spectrum of Monodeuterated Acetamide CH 2

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. Gillemine a. Department b. LISA, CNRS/Universités Paris Est et Paris Diderot, Créteil, France c. Ph. LAM, d. CTCC, e. ISCR, of Physics, Tomsk State University, Tomsk, Russia CNRS/Université de Lille I, Villeneuve d’Ascq, France Dept. of Chemistry, University of Oslo, Norway UMR 6226, Rennes, France

CH 2 DC(=O)NH 2 is of astrophysical relevance & theoretically interesting • Normal species detected in Sagittarius B 2(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) L 25

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. Vi' coefficients are unknown.

Deuteration effects: potential energy function For deuterated methanol, 1 V 3 i' = V 3 i, and { V 1' = 9. 95 cm-1 CH 2 D V 1' = -10. 36 cm-1 CD 2 H In the present case, 2 V 3' = 25. 043, V 6' = -10. 048, and V 1' = ± 10 cm-1 1. Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spec. 256 (2009) 204 2. Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Mol. Spec. 227 (2004) 115

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

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

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 4 x 4 generalized intertia tensor, on 6 potential energy parameters V 1, V 2, V 3, …, and on distortion parameters. 1. Paper RF 10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014) 064307

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 Kdependence.

Torsion-rotation energy levels 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 V 1 = -10 cm-1

The microwave spectra 3 room temperature spectra Stark Modulation 7 Millimeter Wave 80 75 Millimeter Wave 91 Molecular Beam Cold temperature spectrum 5. 8 19 Frequencies are in GHz 150 165

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 Kc-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 Ka = 10 for the e 0 torsional state. The RMS of 0. 9 MHz. The fit degrades when Ka increases.

Torsion-Rotation Hamiltonian fit 171 transitions with J ≤ 12 and Ka ≤ 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 Ka-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. 2 1. Paper RF 10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014) 064307 2. Ilyushin, Alekseev, Dyubko, Kleiner, and Hougen, J. Mol. Spec. 227 (2004) 115

Torsion-Rotation Hamiltonian fit 56. 9 102. 5 48. 7 -2. 0 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.