DISCOVERY OF FULMINIC ACID, HCNO, IN DARK CLOUDS

We report on the first detection in space of fulminic acid, HCNO. This isomer of HNCO has been observed in three starless cores, B1, L1544, and L183, and in the low-mass star-forming region L1527 with a measured abundance ratio of HNCO/HCNO between 40 and 70. However, HCNO was not detected toward the direction of the cyanopolyyne peak of TMC-1 or toward the Orion Hot Core region. The derived HNCO/HCNO abundance ratio in these cases is greater than 350 and 1000 in TMC-1 and Orion, respectively. We find that CH2 + NO -> HCNO + H is a key reaction for the formation of fulminic acid. A value of 5.5 x 10(-12) cm(3) s(-1) of the corresponding reaction rate coefficient, as given by Miller et al., allows us to reproduce the observed abundances of fulminic acid in both the observed dark clouds and low-mass star-forming core, where the determined abundance of HNCO in these regions with respect to molecular hydrogen is 1-5 x 10(-10).