Bochum scientists were successful for the first time in measuring the hyperfine structure of a molecule in a matrix structure. This has the desired effect of allowing one to perform “ultra-cold” chemistry and ultimately study astronomic and atmospheric radical molecules such as CH and OH. In practice, there are two fundamental problems that have to be overcome. Firstly, the object has to be sufficiently cooled in order to simplify the complexity of the spectra. Secondly, a high-resolution diagnostic is necessary to demonstrate the effects. The first problem is solved by embedding NO in helium droplets. Because there is on average only one NO molecule per 3000 helium atoms, one speaks of doping. This process was used in Bochum for the first time on radical molecules. The advantages over the previously-used molecular beams are that:
- You achieve significantly lower temperatures (as low as 0.4 K).
- The radical molecule is “dissolved” in helium and therefore does not react much with its environment.
- The degrees of freedom of rotation and vibration are not suppressed.
- Matrix displacements of the spectra are relatively low.
That is to say, the NO can still be considered a gas. This diagnosis is based on lead salt lasers selected for 1875 or 1818 cm-1. With these lasers, line widths of 0.003 cm-1 can be resolved. It was demonstrated that the hyperfine structure of NO in a helium droplet remains unchanged compared to the free molecule. Thus, the average electron distribution is not affected by the quantum liquid. However, the quantum liquid has an effect on the doublet energy. With the work the Bochum scientists have done, the corner stone has been laid for follow-up experiments throughout the world.
References:
[1] K. von Haeften, A. Metzelthin, S. Rudolph, V. Staemmler and M. Havenith, Physical Review Letters 95,215301 (2005)
