Extensive experiments on the K=3 component of the J=12–11 rotational transition of acetonitrile CH 3 C 14 N, located near 220.7GHz, were performed at different temperatures in the range 235–350K. They allow determining the N 2 -, H 2 -, and He-broadening coefficients, as well as their temperature dependences. More specific measurements on all the K-components of the involved transition perturbed by N 2 at 303K allow to point out a clear decreasing of the broadening coefficient with increasing K. Narrowing effects are clearly observed, and experimental lines were analysed both with Voigt and speed dependent Voigt profiles; but no exhaustive lineshape study was carried out. All the experimental parameters are compared with results derived from a semiclassical calculation of collisional interactions, including electrostatic, induction, and dispersion energy contributions.