@article{10716,
  author = {Y. Demkov and V. Ostrovskii and E. Solov'ev},
  title = {Two-state approximation in the adiabatic and sudden-perturbation limits},
  year = {1978},
  journal = {Physical Review A},
  volume = {18},
  pages = {2089-2096},
  month = {Jan-11-1978},
  issn = {0556-2791},
  url = {http://link.aps.org/doi/10.1103/PhysRevA.18.2089},
  doi = {10.1103/PhysRevA.18.2089},
}