LIFETIME OF METASTABLE MAGNESIUM ATOMS IN SUPERFLUID-HELIUM

The metastable 3s3p P-3(0,1,2) states of the magnesium atom immersed i nto superfluid helium have been investigated. Absorption-fluorescence measurements were carried out to monitor the population of the (3)p(0) , P-3(1) and P-3(2) level as a function of time. The population of the se levels was found to decrease exponentially with a constant of tau = 15 +/- 2 ms. This is about three times as long as the vacuum lifetime of the P-3(1) level. In the resonant excitation band of the 3s3p P-3 states to the 3s4s S-3 State a blueshift of 70 nm compared to the emis sion and a large broadening were detected. The P-3(2) and P-3(0) state s are not at all metastable any more. Additionally the weak intercombi nation transition of the P-3(1) state to the S-1(0) ground state was i nvestigated by monitoring this emission line as a function of time and of wavelength. The experiments resulted in the same exponential decay time as the excitation measurement. This outcome indicates a rather e ffective fine structure mixing of the considered Mg states in superflu id helium. Moreover, this raises the question whether common atomic qu antum numbers are conserved and the selection rules are still valid.