The N-15, C-13. and H-1 absolute magnetic shielding of a CH3 C-13 N-15 molecule has been determined from NMR measurements in the gas phase at 300 K: sigma(o)(C (N) under bar) = -8.873(5) ppm. sigma(o)((C) under barN) = 74.021(3) ppm and sigma(o)(C (H) under bar (3)) = 29.113(1) ppm. It is shown that intermolecular shielding effects for the C-13 and N-15 nuclei in the cyano group are large and in the opposite directions. For the first time the dependence on density has also been observed for the (1)J(NC), (2)J(CH) and (3)J(NH) spin-spin coupling when the HSQC spectra of CH3 C-13 N-15 have been analyzed. It has permitted us to obtain the coupling constants free from intermolecular interactions: (1)J(o)(NC) = -16.20(1) Hz, (2)J(o)(CH) = -10.18(2) Hz and (3)J(o)(NH) = - 1.34(2) Hz. The new experimental results may be useful for the verification of appropriate ab initio calculations for an acetonitrile molecule. (C) 2002 Elsevier Science B.V. All rights reserved.