PRESSURE-DEPENDENT QUENCHING OF RB 5P STATES IN LIQUID-HELIUM

The decay times of D-1 emission lines of Rb and Cs atoms in superfluid helium were measured at 1.6 K as functions of helium pressure in a ra nge from the saturated vapor pressure to about 25 atm. In the case of Cs, the measured decay time is almost independent of the helium pressu re and is given by the lifetime of the 6P(1/2) state of the free atom. However, we have found that the decay time of the Rb D-1 line decreas es with increasing pressure. This suggests the coexistence of two proc esses leading from the excited P state to the ground state, one an ord inary D-1 emission transition and the other a process decaying via a l ower energy state before reaching the ground state. The pressure-depen dent quenching observed only for the Rb atom can be explained by the c ompetition of the above two processes. A possible mechanism for quench ing of the Rb 5P states is discussed in terms of the interaction poten tials of the alkali-metal-atom-He-N system, where two or six helium at oms are localized near the alkali core in a particular anisotropic con figuration. The dynamics of processes leading from the excited P state s of Na and Cs atoms are also discussed.