International Workshop on Atomic Interactions in Laser Fields - Abstracts
G.Lindenblatt, H.Wenz, W.Behmenburg
Institut für Experimentalphysik, H.-H. Universität Düsseldorf, D40225 Düsseldorf
By selective optical excitation of collision pairs and observation of the reemitted fluorescence information is obtained on the potentials and dynamic couplings governing the collision. Due to their simple electronic structure Lithium-rare gas systems are particularely well suited for such optical collision experiments. For the process
Li(2P) + X + hν → LiX(3DΛ) → Li(3P,3D) + X
the branching ratio B := p(3DΛ→3P)/(3DΛ→3D) for dissociation of the LiX(3DΛ) molecules (X = Ne, Ar) into the Li(3P,3D) atomic states has been studied experimentally as function of the laser frequency ν. The experiments were performed using two step cw laser excitation of gaseous mixtures of Li+X at temperatures around 600 K, and the Li(3P,3D) population was monitored, by the fluorescence from these levels, in the detuning range |Δν| ≤ 100 cm-1 of the laser from the Li(2P-3D) transition.
To obtain the spectral profiles B(Δν) for single collisions, the 3P/3D population ratio R(Δν,px) is measured at a fixed pressure px, and the effects of subsequent collisions are eliminated by additional measurements of the px dependence of R(0,px) at resonant excitation.
The B(Δν) profiles thus evaluated display strong blue-red wing asymmetries both for Li(2P)Ne and Li(2P)Ar. This reflects different dissociation probabilities from the 3DΣ or 3D(Π,Δ) states that are initially prepared by blue wing or red wing excitation, respectively. The results are qualitatively discussed in terms of new ab initio potentials for the two systems.
The results for the Li(2P)Ne system are also compared with quantum coupled-channels calculations [1] for the thermally averaged excitation transfer cross sections σ(3DΛ*→3PΛ) and the B(Δν) profile using potentials [2] and coupling matrix elements [3] from ab initio methods as input. The Λ-averaged cross section σ(3D→3P) as well as the B(0) value agree within a factor of about 2 with experimental values. The B(Δν) profile [1] is consistent with an enhanced 3P formation in the red wing.