FORMATION OF AGHE2 EXCIPLEX IN LIQUID-HELIUM

We report the first experimental confirmation of a metal-atom-He excip lex formation in liquid helium. Following the excitation of the D2 lin e of an Ag atom, we have observed the atomic D1 line emission and a br oadband emission to the red of the DI line. The band has been assigned to the (A) over tilde(2) Pi(3/2) - (X) over tilde(2) Sigma(+) bound-f ree transition of the He-Ag-He linear exciplex trapped in a microcavit y in liquid helium. The assignment has been confirmed by an ab initio calculation on the AgHe2 molecule. The absence of the atomic D2 emissi on as well as an emission from AgHe indicates that the P-2(3/2)-->P-2( 1/2) relaxation and the formation of AgHe2 in the (A) over tilde(2) Pi (3/2), upsilon' = 0 State occur on a subnanosecond time scale.