A Survey of Magnetic Field Strengths in the Envelopes of Molecular
  Clouds via the 18 cm OH Zeeman Effect
  We present the results of an extensive Arecibo observational survey of
magnetic field strengths in the inter-core regions of molecular clouds to
determine their role in the evolution and collapse of molecular clouds as a
whole. Sensitive 18 cm OH Zeeman observations of absorption lines from Galactic
molecular gas in the direction of extragalactic continuum sources yielded 38
independent measurements of magnetic field strengths. Zeeman detections were
achieved at the three sigma level toward 9 clouds, while the others revealed
sensitive upper limits to the magnetic field strength. Our results suggest that
total field strengths in the inter-core regions of GMCs are about 15
microgauss.
