These are not polar molecules. Electrons are not equally distributed at one instant which gives a small instantaneous dipole and the molecule itself becomes a small dipole. Dipoles are oriented in space so there is attraction to a second molecule. The strength of this force depends on the ease with which the electron cloud of the molecule is distorted. The electron of a large molecule are further from the nucleus, therefore are more easily distorted to give instantaneous dipoles.
Vapor pressure is a property of liquids and solids.
Because of evaporation, the open space above any liquid contains some molecules of liquid in the gas phase. This is true of solids as well as gases. The reason for this is that some molecules have enough kinetic energy to overcome the attraction of neighboring molecules and gravity to escape into the gas phase. . If the gas space is closed, the vapor pressure will increase to a definite value for a given temperature and remain there. This is called the equilibrium vapor pressure. .