  Accurate modeling of physical and chemical processes in the interstellar
medium requires detailed knowledge of how atoms and molecule adsorb on dust
grains. However, the sticking coefficient, a number between 0 and 1 that
measures the first step in the interaction of a particle with a surface, is
usually assumed in simulations of ISM environments to be either 0.5 or 1. Here
we report on the determination of the sticking coefficient of H$_2$, D$_2$,
N$_2$, O$_2$, CO, CH$_4$, and CO$_2$ on non-porous amorphous solid water
(np-ASW). The sticking coefficient was measured over a wide range of surface
temperatures using a highly collimated molecular beam. We showed that the
standard way of measuring the sticking coefficient --- the King-Wells method
--- leads to the underestimation of trapping events in which there is
incomplete energy accommodation of the molecule on the surface. Surface
scattering experiments with the use of a pulsed molecular beam are used instead
to measure the sticking coefficient. Based on the values of the measured
sticking coefficient we suggest a useful general formula of the sticking
coefficient as a function of grain temperature and molecule-surface binding
energy. We use this formula in a simulation of ISM gas-grain chemistry to find
the effect of sticking on the abundance of key molecules both on grains and in
the gas-phase.
