We present an experimental technique enabling a direct observation of the momentum transfer distribution generated by rotationally inelastic molecular collisions of ${\mathrm{CO}}_2$ with ${\mathrm{H}}_2$, He, ${\mathrm{CO}}_2$, and Kr. The observations indicate that the rotational transition results primarily from peripheral collisions which are effective in transferring angular momentum, but which communicate a relatively small linear momentum transfer. The mean change in the $z$ component of velocity is presented for ${\mathrm{CO}}_2$-${\mathrm{H}}_2$ collisions.

• Received 14 January 1974

DOI:https://doi.org/10.1103/PhysRevLett.32.637