ABSOLUTE MEASUREMENT OF DIELECTRONIC RECOMBINATION FOR C3-FIELD( IN AKNOWN EXTERNAL)

An absolute measurement of the rate coefficient for dielectronic recom bination (DR) of C3+, via the 2s-2p core excitation, in an external el ectric field of 11.4+/-0.9(1 sigma) V cm(-1) is presented. An inclined -beam arrangement is used and the stabilizing photons at similar to 15 5 nm are detected in delayed coincidence with the recombined ions. The full width at half maximum of the electron energy spread in the ion r est frame is 1.74+/-0.22(1 sigma) eV. The measured DR rate, at a mean electron energy of 8.26+/-0.07(1 sigma) eV, is (2.76+/-0.75) x 10(-10) cm(3) s(-1). The uncertainty quoted for the DR rate is the total unce rtainty, systematic and statistical, at the 1 sigma level. In comparin g the present results to theory, a semiempirical formula is used to de termine which recombined ion states are ionized by the 4.65 kV cm(-1) fields in the final-charge-state analyzer and not detected. For the pr esent results, any DR of the incident electrons into n levels greater than 44 is assumed to be field ionized in the final-charge-state analy zer. A more precise treatment of field ionization, which includes the lifetime of the C2+ ions before they are ionized and the time evolutio n and rotation of the fields experienced by the recombined ions, is ne eded before a definitive comparison between experiment and theory can be made. Our DR measurement, within the limits of that approach, agree s reasonably well with an intermediate coupling calculation that uses an isolated resonance, single-configuration approximation, but does no t agree with pure LS-coupling calculations.