@article{11521,
  author = {E. Smith and C. Vidal and John Cooper},
  title = {Classical path methods in line broadening. I. The classical path approximation},
  year = {1969},
  journal = {Journal of Research of the National Bureau of Standards},
  volume = {73A},
  pages = {389-404},
  url = {http://archive.org/details/jresv73An4p389},
  note = {JILA Pub. 457},
}