ELECTRON ABUNDANCE IN DENSE CLOUD CORES - IMPLICATIONS FOR STAR-FORMATION

By combining observations of the J = 1 --> 0 transitions of (CO)-O-18 and (HCO+)-C-13, and the J = 1 --> 0 and 2 --> 1 transitions of DCO+, and a model of molecular cloud chemistry, we have obtained the electro n abundance (X-e drop n(e)/n(H2)) in a sample of 20 low-mass and 7 hig h-mass molecular cloud cores. We find that the electron abundances are confined to a relatively narrow range of -7.5 < log(X-e)< -6.5 with v ery little scatter about the mean values of < log(X-e)> = -7.04; sigma = 0.22 (low-mass cores) and < log(X-e)> = -7.11; sigma = 0.15 thigh-m ass cores). These values are consistent with the standard view that th e ionization in dense cloud cores is dominated by cosmic rays, provide d that zeta(H2) approximate to 5 x 10(-17) s(-1). These electron abund ances also imply that the neutrals are only marginally coupled to the magnetic field (W approximate to 5-8) with only ca. 10% the core radiu s being cut off from magneto-hydrodynamic (MHD) wave propagation. The coupling parameter (RI) also suggests that ambipolar diffusion timesca les are about an order of magnitude larger than the freefall timescale .