The technique of matrix isolation has extensively been used to study reactive species which are isolated in an inert host matrix, preventing in this way diffusion or reaction of the trapped species. The present study is concerned with the theoretical description of matrix trapping dynamics. The most common experimental technique of matrix deposition, slow spray on, is simulated using classical molecular dynamics. The systems considered are simple spherical species trapped in argon. The effect of the size of the trapped species on-the structure of the matrix and the nature of the trapping site is investigated.