Molecular beam measurements of total collision cross sections of H2O

The total cross section for H2O–H2O scattering is measured with a supersonic nozzle beam system. The primary beam has a narrow velocity distribution, and the velocity is varied by control of the nozzle temperature. Velocities are determined by time-of-flight techniques. Cross sections obtained are averages over a Maxwellian distribution of the target molecules. Data at three velocities are presented. The cross sections for H2O are surprisingly small, for example, 3.07× 10−14 cm2 at 1× 105 cm/sec, indicating little contribution from the dipole-dipole interaction.