Abstract
Using the VLA we searched for H I in absorption against the continuum of seven compact planetary nebulae. With the exception of the previously reported feature in NGC 6302, all observed absorption lines can be attributed to line of sight clouds unrelated to the planetary nebulae. Typical upper limits for associated H I are < 0.01 M®. Theoretical considerations (Glassgold and Huggins 1983) suggest that detectable H I may exist only for planetary nebulae with relatively hot (T* > 2500 K) progenitors. It is also expected theoretically that these stars will produce considerable nitrogen enrichment. In agreement with these notions, NGC 6302 one of the largest N/O ratios observed in planetary nebulae.
