1. Could you explain the significance of your article to the non-specialist?

Lutetium is an uncommon metal, which is difficult to separate from other rare-earth metals because of their similar chemistries.  Few simple Lu compounds have been studied spectroscopically, and comparatively little is known about the nature of their bonding. 

Our studies of LuF and LuCl have allowed us to identify the molecules, measure their bond lengths to femtometer accuracy, obtain a picture of their electron distributions, and evaluate their vibration frequencies and dissociation energies, using a single experimental technique, microwave rotational spectroscopy. 

Remarkably, Lu is of astrophysical importance, and the work is a first step towards identifying Lu compounds in interstellar space.

2. What has motivated you to conduct this work?  

Microwave spectroscopy is a gas phase technique.  The combination of Fourier transform microwave spectroscopy, supersonic jets and laser ablation has permitted spectra to be measured of many reactive molecules otherwise difficult to study. 

Very recently we have applied it to compounds containing high melting metals, with often surprising discoveries (e.g. confirmation of the existence of AuF (JACS, 2000, 122, 9363), XeAu chemical bonding in XeAuF (JACS, 2004, 126, 17000), and the first experimental detection of PtCO (JPC, 2001, A105, 9659)).  Lutetium melts at 1652 C, and we hoped to prepare and characterize some of its compounds, starting with LuF and LuCl. Primarily we would measure their bond lengths. 

Because the spectral measurements are so precise, we expected to observe breakdown of the Born-Oppenheimer approximation, including the need to account for the finite volume of the Lu nucleus. 

In addition, Lu has a high nuclear spin and a large quadrupole moment, so that detailed information on the molecular electronic structure would be available. The astrophysical significance also aroused our interest. Clearly our expectations have been met!

3. Where do you see this work developing in the future?
            
Application of the technique to metal compounds, especially those containing heavy metals, is barely past its infancy. As we have shown, it is a relatively simple, relatively inexpensive method to obtain much fundamental information about the bonding characteristics, molecular and electronic structures and potential energy surfaces of such molecules.

Eventually these studies will progress from simple closed shell molecules to open shell species, more complex molecules, and ions.

For Lu in particular, we are extending the work to paramagnetic LuO, which has a better chance than LuF or LuCl of being found in the interstellar medium.

4. Are there any particular challenges facing future research in this area?

Obtaining good quality spectra of any type is a challenge.  As the molecules become more exotic and unusual there will be many hurdles. Synthetic procedures will become more elaborate. Quantities of sample may well be small, leading to difficulties with detection.  Unusual molecules may well provide unusual spectral patterns leading to troublesome spectral analyses. 

However, such challenges are not insurmountable, and the results of efforts to deal with them should be of interest to chemists working in many different areas.