The torsional spectrum of doubly deuterated methanol CHD

The torsional spectrum of doubly deuterated methanol CHD 2 OH M. Ndao, a L. H. Coudert, a F. Kwabia Tchana, a J. Barros, b L. Margulès, c L. Manceron, b and P. Royb a. LISA, CNRS/Universités Paris Est et Paris Diderot, Créteil, France b. AILES beam line, Synchrotron Soleil, Gif-sur-Yvette, France c. Ph. LAM, CNRS/Université de Lille I, Villeneuve d’Ascq, France

Molecules displaying internal rotation of a partially deuterated methyl group

Overview • Qualitative differences between CD 2 HOH and CH 2 DOH • The available microwave and FIR spectra • Assignment and fit of the FIR spectrum • Assignment and fit of the microwave spectrum

Qualitative differences between CD 2 HOH and CH 2 DOH CD 2 HOH

CH 2 DOH CD 2 HOH

K-dependence of the torsional energy Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spec. 256 (2009) 204

Experimental FIR spectra 4 high-resolution FIR spectra were recorded using a Fourier transform spectrometer coupled to a White-type cell. Spectra were recorded under the following experimental conditions: • 19 -58 cm-1 • 38 -670 cm-1 • 48 -226 cm-1 • 58 -670 cm-1 P = 0. 252 mbar P = 0. 81 mbar P = 0. 44 mbar P = 0. 248 mbar L = 725 cm L = 85 cm L = 725 cm For all spectra the resolution was 0. 00102 cm-1.

Torsional spectrum analysis Torsional subband centers were calculated using the approach developed for CH 2 DOH. 1 • The 8 parameters describing the 4 ☓ 4 generalized inertia tensor were calculated from the structure of the molecule. • The potential energy function retrieved through ab initio calculations by Lauvergnat et al. 2 was taken. K=13, v=0 ← 12, 1 K=6, v=4 ← 5, 3 1. El Hilali, Coudert, Konov, and Klee, J. Chem. Phys. 135 (2011) 194309 2. Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spec. 256 (2009) 204

Torsional spectrum analysis K=6, v=9 ← 7, 4 30 torsional subbands assigned. A total of 45 subbands centers were analyzed leading to a refined potential energy function and improved kinetic energy parameters. 1 1. El Hilali, Coudert, Konov, and Klee, J. Chem. Phys. 135 (2011) 194309

Experimental microwave spectrum The microwave spectrum was recorded in Lille from 75 to 622 GHz.

Assignment of the microwave spectrum The assignments published by Quade and coworkers 1 -2 were used as a starting point. • a-type transitions with K=0, 1, and J ≤ 2 for e 0, o 1, and e 1. • b- and c-type transitions with ΔK= 1, K ≤ 2 , and J ≤ 9 for the same levels. K=4, e 1 ← 3, e 1 1. Su and Quade, J. Chem. Phys. 90 (1989) 1396 2. Quade, Liu, Mukhopadhyay, and Su, J. Mol. Spec. 192 (1998) 378

Assignment of the microwave spectrum The microwave spectrum was assigned using a bootstrap method with the torsion-rotation approach developed for CH 2 DOH. 1 910 transitions could be assigned up to J = 20 and K = 6 and fitted with an RMS of 0. 5 MHz. 1. Paper RF 10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014) 064307

a-type transitions with K=0 within o 1 Like in CH 2 DOH, torsional levels with low K-values are perturbed. 1 I. J(J+1) expansion with B, D, and H. II. Torsion-rotation approach. 1. Pearson, Yu, and Drouin, J. Mol. Spec. 280 (2012) 119

Lowest lying torsional levels Levels with K > 3 are not perturbed e 0 o 1 e 1

Assigned microwave transitions ?

Spectroscopic constants 2. 444 x 10 -2 2. 409 x 10 -2 6. 067 x 10 -2 -9. 819 x 10 -2 1. 569 x 10 -2 -1. 100 x 10 -2 -1. 079 x 10 -2 5. 317 x 10 -2 -10. 364 x 102 -7. 012 x 102 372. 210 x 102 a Constrained value

Conclusion We are hoping to build for CD 2 HOH a line list (frequencies + intensities) allowing us to determine the abundance of this molecule in the ISM.