Complete density matrix measured for Na(32 P) excited by electron impact

Abstract

Anisotropies observed in collisional deexcitation of laser excited Na atoms are analysed in terms of the density matrix describing the Na(3P) atom after the process Na(32 S)+e −(E)→Na(32 P)+e −(E−δE). Collision energiesE range from 5.1 to 22.1 eV, and scattering angles fromθ col=0 to 25°. The results are presented with reference to a coordinate frame in which the angular momentum transferred during collision is parallel to the quantization axis. This choice allows a convenient exploitation of reflection symmetry and offers most direct relation of measurable quantities to the sublevel excitation amplitudes as e.g. computed by close coupling and distorted wave methods. Comparison between experiment and theory provides a sensitive probe of the strengths and shortcomings of the theory when predicting these alignment and orientation parameters. Since we discuss a complete set of data containing all accessible information on the atomic orbital the present measurements allow the detection of a deviation from coherence in the excitation for small scattering anglesθ col≈5–10° atE=5.1 eV which we attribute to electron exchange.