We present a diabatic approach to the dynamics of electronically adiabatic chemical reactions. A method is proposed for constructing diabatic surfaces from a single adiabatic potential surface. By using diabatic surfaces we can choose natural coordinate systems for both the reactant and product arrangements. The diabatic approach can be easily adapted to exact quantum mechanical calculations based on variational scattering formulations. The square integrable basis functions are obtained by diagonalizing the total Hamiltonian matrix which is constructed from the separate eigenfunctions on the reactant and product diabatic surfaces. Applications to one-dimensional barrier problems and the collinear H+H-2-->H-2+H reaction demonstrate the feasibility of the diabatic approach. At low total energies, reaction probabilities for adiabatic reactions can be reproduced by the present method. Moderately accurate results can be obtained at high total energies for the collinear H+H-2-->H-2+H reaction, which may be improved by the optimal construction of diabatic surfaces.