1. The torsional spectrum of doubly deuterated methanol CHD2OH
M. Ndao,a L. H. Coudert,a F. Kwabia Tchana,a
J. Barros,b L. Margulès,c L. Manceron,b and P. Royb
aLISA, CNRS/Universités Paris Est et Paris Diderot, Créteil, France
bAILES beam line, Synchrotron Soleil, Gif-sur-Yvette, France
cPhLAM, CNRS/Université de Lille I, Villeneuve d’Ascq, France

2. Molecules displaying internal rotation of a partially deuterated methyl group

3. Overview Qualitative differences between CD2HOH and CH2DOH
The available microwave and FIR spectra
Assignment and fit of the FIR spectrum
Assignment and fit of the microwave spectrum

4. Qualitative differences between CD2HOH and CH2DOH

5. CH2DOH
CD2HOH

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

7. 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 P = mbar L = 725 cm
cm-1 P = 0.81 mbar L = 725 cm
cm-1 P = 0.44 mbar L = 85 cm
cm-1 P = mbar L = 725 cm
For all spectra the resolution was cm-1.

8. Torsional spectrum analysis
Torsional subband centers were calculated using the approach developed for CH2DOH.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)
2. Lauvergnat, Coudert, Klee, and Smirnov, J. Mol. Spec. 256 (2009) 204

9. 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)

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

11. Assignment of the microwave spectrum
The assignments published by Quade and coworkers1-2 were used as a starting point.
a-type transitions with K=0, 1, and J ≤ 2 for e0, o1, and e1.
b- and c-type transitions with ΔK= 1, K ≤ 2 , and J ≤ 9 for the same levels.
K=4, e1 ← 3, e1
1. Su and Quade, J. Chem. Phys. 90 (1989) 1396
2. Quade, Liu, Mukhopadhyay, and Su, J. Mol. Spec. 192 (1998) 378

12. Assignment of the microwave spectrum
The microwave spectrum was assigned using a bootstrap method with the torsion-rotation approach developed for CH2DOH.1
910 transitions could be assigned up to J = 20 and K = 6 and fitted with an RMS of 0.5 MHz.
1. Paper RF10, Columbus 2013; and Coudert, Zemouli, Motiyenko, Margulès, and Klee, J. Chem. Phys. 140 (2014)

13. a-type transitions with K=0 within o1
Like in CH2DOH, 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

14. Lowest lying torsional levels
Levels with K > 3 are not perturbed
e o e1

15. Assigned microwave transitions?

16. Spectroscopic constants
2.444 x 10-2
2.409 x 10-2
6.067 x 10-2
x 10-2
1.569 x 10-2
x 10-2
x 10-2
5.317 x 10-2
x 102
x 102
x 102
aConstrained value

17. Conclusion
We are hoping to build for CD2HOH a line list (frequencies + intensities) allowing us to determine the abundance of this molecule in the ISM.