We are proposing a new formulation on the condensation coefficient of vapor molecule at liquid-vapor interface based on molecular dynamics (MD) studies and transition state theory. The equation is a function of translation energy of incident vapor molecule and surface temperature, which indicates that the condensation probability is not uniform for all incident molecules but is dependent on the kinetic situation during the interaction between vapor and surface molecules. Considering behaviors of evaporating and reflecting molecules at the liquid surface as well as the condensing probability, the velocity distributions of the evaporating and the reflecting molecules have been expressed with use of the condensation coefficient. The direct simulation Monte Carlo (DSMC) analysis shows that the dependence of the condensation coefficient on translation energy plays an important role in the temperature profiles. The transition state theory gives us the theoretical expression of the condensation coefficient and it is found that MD data for argon, water and methanol agree very well with the theoretical expression. But the experimental data for water show smaller values than the theoretical ones. We are considering the differences are due to the existence of non-condensable gases in the experimental system. A non-equilibrium MD study is also included in this paper for a discussion on the inverted temperature profiles. (C) 2004 Elsevier Ltd. All rights reserved.