collision tracking in poiseuille flow

Hi,
i am simulating a poiseuille flow in which i have to calculate the
Accommodation coefficients. to calculate the coefficients i want to get
the average incident and reflected velocity of gas particles with the
wall. my gas molecules are argon and wall molecules are made of platinum.

do we have any method or command so as to track the these average incident
and reflected velocities..

Thank you

If your wall is made of atoms, how are you defining
a “collision” between a flow atom and the wall?

Steve