Interstellar detection of deuterated methyl cyanide.

Deuterated methyl cyanide has been detected towards the hot core of IRc2 in OMC1 with a D/H isotopic ratio of about 0.01. This species presents two states not connected by collisional or radiative transitions (ortho and para) whose expected ratio is 3:1. Our data suggests that the observed ratio is close to 1, as if the molecules of CH2DCN have not had time to reach the statistical equilibrium. We have also detected tentatively CH2DCN towards G34.3, with the same isotopic ratio (D/H is less than about 0.01); in this source the ortho species seems to be more abundant than the para species.