Pressure dependence of the Mg $3s4s^3S_1 \to 3s3p^3P_{0,1,2}$ transition   in superfluid $^4$He
  The pressure shifts of the $3s4s^3S_1 \to 3s3p^3P_{0,1,2}$ transition of magnesium atoms immersed in superfluid helium have been measured at $(1.3\pm0.1 )$K between saturated vapour pressure and $24 $bar. The wavelength is blue shifted linearly by $(0.07\pm0.01) \frac{nm}{bar}$. This value can be satisfactorily described in the framework of the standard bubble model. 
I. Baumann (1) A. Breidenassel (1) C. Z\"uhlke (1) A. Kasimov (1) G.   zu Putlitz (1) I. Reinhard (1) K. Jungmann (1) ((1) U...