Light-induced viscous flow of a one-component gas

A new phenomenon, light-induced viscous flow in a one-component gas, is observed in ${\mathrm{CH}}_3$F upon velocity-selective vibrational excitation. The effect originates from a state-dependent kinetic collision rate in combination with nonuniform illumination. The theory for this effect is derived using a Chapman-Enskog approach. Good agreement between theory and experiments in the near-hydrodynamic regime is found.