NEW UPPER LIMITS ON THE INTERSTELLAR O2 ABUNDANCE

We report new observations of molecular oxygen in absorption atz =0 :685 in front of the radio source B0218+357. The lines at 56.3 and 118.7 GHz have been observed, redshifted to 33.4 and 70.5 GHz respectively, with the 12m at Kitt Peak, 43m at Green Bank telescopes, and the 45m Nobeyama radio telescope. Deriving the surface lling factor of the absorbing dark cloud with other lines detected at nearby frequencies, we deducefromtheupperlimitsontheO2linesarelativeabundance ofmolecularoxygenwithrespecttocarbonmonoxydeofO2/CO < 21 0 3 at 1, seven times lower than the previous limit. The consequences of this result are discussed.