MEASUREMENT OF THE H(N=2) DENSITY-MATRIX FOR 20-100-KEV COLLISIONS OFH+ ON HE

Density matrices are experimentally determined which describe H(n = 2) atoms produced in electron-transfer collisions between 20-100-keV pro tons and helium. The density matrix contains the electron-transfer cro ss sections sigma2s, sigma2p0, and sigma2p(+/-1), as Well as the real and imaginary parts of the s0p0 coherence. Experimentally, a monoenerg etic proton beam traverses a helium gas cell producing hydrogen atoms H(n) via electron transfer. Within the gas cell an electric field is a pplied either axial or transverse to the proton beam. The Stokes param eters describing the intensity and linear polarization of Lyman-a radi ation (122 nm) emitted by H(n =2) atoms are determined as a function o f applied electric-field strength. The density-matrix elements are det ermined from a linear least-squares fit of the Stokes parameters to th e set of five fitting functions which represent the contributions from individual density-matrix elements. The density-matrix results are se lf-consistent. Separate determinations using axial or transverse elect ric fields agree with each other. The general results indicate sigma2s > sigma2p0 > sigma2p(+/-1) between 20 and 100 keV. The electric dipol e moment [d]z has a value near zero at 20 keV rising to a maximum of a bout 1.3 a.u. near 40 keV and remaining nearly constant through 100 ke V. The [L X A]z,s moment has a maximum of about 0.5 a.u. at 25 keV, pa ssing through zero near 70 keV. These results compare favorably with a vailable experimental results and are qualitatively predicted by prese nt theoretical models. Comparison with previous H(n = 3) results indic ates that the Runge-Lenz vector [A]z is larger for n = 3 than for n = 2 and that [L X A]z,s has the same values for both n.