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The classical molecular dynamics simulation has been used to study the equation of state of gas H2, D2 and T2. It has also been investigated that the isotope mass affects on the accuracy of equation of state. Our calculated results show that the classical effect is principal and the isotope mass effects on the equation of state are obvious for the much light gases. At the same time, some useful theoretical data of equation of state for these gases have been provided. It is found that the classical simulation is still effective to the quantum gas. However, the quantum mechanics simulation and the improvement of intermolecular interaction potential are necessary if more accurate computational results are expected.

Close-coupling method was applied to the 3He（4He,5He）-H2 system, and the second vibrational excitation cross sections of “00-20，00-22，00-24，00-26” at different incident energies have been calculated．By analysing the differences of these partial wave cross sections, the change rules of how the partial wave cross sections change with the mass of isotope atom and the relative kinetic energy of incident atoms are obtained.

Differential cross sections (DCSs) for collisions in 3He-HBr, 4He-HBr, 6He-HBr and 7He-HBr are calculated by the close-coupling approach from the anisotropic intermolecular potential of the He-HBr system established by the author. The calculations are performed separately at the collision energies of 40 and 75 meV. The influence of the incident isotope He atoms on DCSs is discussed in detail. The results show that the angular distribution of the total DCSs at zero degree increases and the position of oscillation minimum of the same order gradually shifts towards small scattering angle along with the increase of the incident isotope He atom mass at identical collision energy. And crossing angle between the elastic and total inelastic DCSs gradually decreases and the total inelastic DCS gradually increases. The rainbow phenomenon becomes more evident the lower the collision energy and the larger mass of the incident He isotope atom.

The total differential cross section, elastic differential cross section and inelastic differential cross section for collision between He isotopic atoms and NO molecule have been calculated by using close-coupling approximation method. The influence of He isotope on the differential cross section for He-NO collision system has been given. The calculated result shows that the total differential cross section at 0 degree increases, and rainbow phenomenon of collision of He isotopic atoms with NO molecule is more evident along with increase of incident He isotope mass at identical incident energy. At the same time, the effect of increased reduced mass is larger than the effect of diminished relative velocity of collision between He atom and NO molecule, and enables the scattering spacing of the oscillation to gradually decrease.