The search for primordial 3He using the 8.665 GHz hyperfine spin-flip transition of 3He+

Frequency-switched observations of the 8.665 GHz hyperfine spin-flip transition of He-3(+) have been made in eight Galactic H II regions in both the inner and outer Galaxy. For sources in the outer Galaxy, the observations reported here show no evidence for He-3(+) to levels well below the level of detections claimed by Bania et al. using the position-switching technique. There is strong evidence that weak terrestrial interference is the explanation for the variability and relatively high level of He-3(+) previously reported in several outer Galaxy sources. In the inner Galaxy, He-3(+) is detected in W43, M17S, and W51 at abundance levels similar to those reported by Balser et al. with He-3(+)/H(+)similar to(1-2) x 10(-5). Contrary to what has been reported previously, the He-3(+)/H+ abundances are found to decrease rapidly with increasing distance from the Galactic center and fall below detectable levels by the Galactic radius of W49 (similar to 8 kpc). This fall-off in second-generation He-3 abundance with distance from the Galactic center is similar to what is predicted by the P-d = 0 model of Galli et al. but is at least a factor of 5 under-abundant. The upper limit to the antenna temperatures obtained here for the He-3(+) lines in Orion A, W49, and S209 gives an upper limit for the abundance of primordial He-3 that is an order of magnitude below the upper limit suggested by Bania et al. This leads to a lower limit for the nucleon-to-photon ratio eta that is at least an order of magnitude above the narrow limits set by Li-7 and deuterium. Possible explanations for this are that there is a larger than expected uncertainty in determining He-3 abundances or that some mechanism is destroying primordial He-3 in the Galaxy over a Hubble time.