Global Analysis Of The Cd₂hoh Molecule Rotation-torsion Spectrum

Doubly deuterated methanol CD$_2$HOH is a non-rigid molecule displaying internal rotation of its asymmetrical CD$_2$H methyl group. Like the isotopic species of methanol with a symmetrical CH$_3$ or CD$_3$ group, it displays a strong rotation-torsion Coriolis coupling. Unlike these species, it also displays a dependence of its generalized inertia tensor on the angle of internal rotation. Its complicated rotation-torsion spectrum was investigated in the microwave,\footnote{Liu and Quade, {\em J.\ Mol.\ Spectrosc.}~{\bf 146} (1991) 252; Su, Liu, and Quade, {\em J.\ Mol.\ Spectrosc.}~{\bf 149} (1991) 557; Quade, Liu, Mukhopadhyay, and Su, {\em J.\ Mol.\ Spectrosc.}~{\bf 192} (1998) 378; Su and Quade, {\em J.\ Chem.\ Phys.}~{\bf 90} (1989) 1396} submillimeter-wave,\footnotetext[2]{Ndao, Tchana, Coudert, Motiyenko, Margul\`es, Barros, Manceron, and Roy, {\em J.\ Mol.\ Spectrosc.}~{\bf 326} (2015) 136}\footnotetext[3]{Mukhopadhyay, {\em Inf.\ Phys.\ Tech.}~{\bf 75} (2016) 139; {\em ibid.}~{\bf 76} (2016) 116}\footnotetext[4]{Mukhopadhyay and Billinghurst, {\em Inf.\ Phys.\ Tech.}~{\bf 113} (2021) 103563}$^{b,c}$ terahertz,$^b$ and FIR$^{b,c,d}$ domains. Although more than 3000 transitions have been assigned so far, no global analysis, like the one performed for the analogous species CH$_2$DOH,\footnotetext[5]{Coudert, Zemouli, Motiyenko, Margul\`es, and Klee, {\em J.\ Chem.\ Phys.}~{\bf 140} (2014) 064307}$^e$ has been carried out. In this talk, new assignments in the terahertz and FIR spectra of CD$_2$HOH will be reported. Parallel and perpendicular transitions, characterized by a higher $K$-value than in our previous investigation,$^b$ could be identified up to $J=35$ for the three lowest lying torsional states. Using the theoretical approach developed for CH$_2$DOH,$^e$ a global analysis of the available high-resolution data could also be carried out and parameters describing the hindering potential and the generalized inertia tensor\footnotetext[6]{Liu and Quade, {\em J.\ Mol.\ Spectrosc.}~{\bf 146} (1991) 238; El Hilali, Coudert, Konov, and Klee, {\em J.\ Chem.\ Phys.}~{\bf 135} (2011) 194309}$^f$ were determined. So far, this global analysis has been restricted to transitions with $K\leq 9$ as rotation-torsion levels with $K>9$ are affected by a yet non-identified rotation-torsion couplings and cannot be properly modeled