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We present N2D+ 3-2 (IRAM) and H2D+ 1_11 - 1_10 and N2H+ 4-3 (JCMT) maps ofthe small cluster-forming Ophiuchus B2 core in the nearby Ophiuchus molecularcloud. In conjunction with previously published N2H+ 1-0 observations, the N2D+data reveal the deuterium fractionation in the high density gas across Oph B2.The average deuterium fractionation R_D = N(N2D+)/N(N2H+) ~ 0.03 over Oph B2,with several small scale R_D peaks and a maximum R_D = 0.1. The mean R_D isconsistent with previous results in isolated starless and protostellar cores.The column density distributions of both H2D+ and N2D+ show no correlation withtotal H2 column density. We find, however, an anticorrelation in deuteriumfractionation with proximity to the embedded protostars in Oph B2 to distances>= 0.04 pc. Destruction mechanisms for deuterated molecules require gastemperatures greater than those previously determined through NH3 observationsof Oph B2 to proceed. We present temperatures calculated for the dense core gasthrough the equating of non-thermal line widths for molecules (i.e., N2D+ andH2D+) expected to trace the same core regions, but the observed complex linestructures in B2 preclude finding a reasonable result in many locations. Thismethod may, however, work well in isolated cores with less complicated velocitystructures. Finally, we use R_D and the H2D+ column density across Oph B2 toset a lower limit on the ionization fraction across the core, finding a meanx_e, lim >= few x 10^{-8}. Our results show that care must be taken when usingdeuterated species as a probe of the physical conditions of dense gas instar-forming regions.

The Initial Conditions of Clustered Star Formation III. The Deuterium Fractionation of the Ophiuchus B2 Core