We have searched for the 2 mm transitions of H 2 C O H + ( 2 02 − 1 01 ) and H 2 13 C O ( 2 02 − 1 01 , 2 12 − 1 11 , a n d 2 11 − 1 10 ) toward the dense interstellar molecular clouds Orion A, TMC-1 and L134N using the FCRAO 14 m telescope. None of the transitions have been detected except the H 2 13 C O transitions toward Orion-KL. We set upper limits for the abundances of the protonated formaldehyde ion ( H 2 C O H + ) , which are close to the abundances expected from ion-molecule chemistry.

• MCGONAGLE D.(Five College Radio Astronomy Observatroy and Department of Physics and Astronomy, University of Massachusetts)
• IRVINE W. M.(Five College Radio Astronomy Observatroy and Department of Physics and Astronomy, University of Massachusetts)
• MINE Y. C.(Korea Astronomy Observatory)