Geometry of three convex bodies applicable to three-molecule clusters in polyatomic gases

An expression for the configuration integral for three overlapping convex bodies, which is a generalization of Hadwiger-Isihara's formula for two convex bodies, has been found. As an application of this expression, two- and three-molecule cluster integrals (or second and third virial coefficients) for polyatomic molecules in gases are discussed on the basis of a squarewell potential with convex cores.