The HOOD Molecule - Internal Rotor and Interstellar Molecule

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The Kassel Laboratory Astrophysics Group, newly founded in 2012, is focusing one of its projects on the simply deuterated form of hydrogen peroxide: the HOOD molecule.
In this molecule, unlike in hydrogen peroxide (HOOH), one hydrogen atom is replaced by a deuterium atom (heavy hydrogen).

In its ground vibrational state (i.e., when it is not undergoing internal vibrations), this molecule exists in two chiral (enantiomeric) forms that can interconvert and are separated only by an unusually low energy barrier. For this reason, a relatively small amount of energy is sufficient to allow HOOD to overcome this barrier and excite it into internal rotations. In this process, the OH and OD subgroups rotate around the OO axis of the molecule.

Fig. 1: In its ground state, the HOOD molecule exists in two chiral (enantiomeric) forms.

Fig. 2: During internal rotation of HOOD, the H and D atoms rotate about the O-O axis.

Because HOOD can be so easily excited into internal rotation, and because, as a four-atom molecule, it represents the simplest possible form of an internal rotor molecule, it is an ideal subject of study for investigating the internal dynamics of molecular systems.

Internal rotor molecules have a significantly more complex spectrum than “rigid” molecules. By recording and analyzing the spectrum of such a molecule, one can gain a great deal of information about the laws governing internal rotation.

Apart from the significance of HOOD spectrum analysis for molecular physics, the molecule is also of astrophysical interest. The non-deuterated form HOOH was first detected in the interstellar medium in 2011 by P. Bergman et al. Among other things, it is considered an important indicator of water formation in space, a process whose origins in the interstellar medium have not yet been fully elucidated.

Fig. 3: The Rho Ophiuchi A star-forming region, where hydrogen peroxide was first detected in space in 2011.

As part of our HOOD project, comprehensive measurements of the molecule’s rotational-vibrational spectrum were conducted at the“SOLEIL” particle accelerator facility in France. In addition, further, higher-resolution measurements of particularly interesting regions of the spectrum are being carried out in our research group’s laboratories in Kassel, as well as through close scientific collaboration with the Laboratory Astrophysics Group at the University of Cologne.
The measurements and data analysis are being carried out as part of a doctoral dissertation and promise new insights into the internal rotation of HOOD in particular and the laws governing the internal dynamics of molecules in general.

As the “culmination” of the project, we will apply for observing time on the 30-meter IRAM telescope in the Sierra Nevada, Spain, in collaboration with observational astronomers. Using the knowledge gained in the lab about the HOOD spectrum, we will attempt to detect the molecule in the interstellar medium.

We have an interesting, experimental master’s thesis opportunity available for this project.
Call for applications for the master’s thesis on HOOD.

Contact the project leader and the doctoral candidate supervising the master’s thesis:
herberth[at]physik.uni-kassel[dot]de