To cite rsm in publications use:

Russell V. Lenth (2009). Response-Surface Methods in R, Using rsm. Journal of Statistical Software, 32(7), 1-17. URL http://www.jstatsoft.org/v32/i07/.

Corresponding BibTeX entry:

  @Article{,
    title = {Response-Surface Methods in {R}, Using {rsm}},
    author = {Russell V. Lenth},
    journal = {Journal of Statistical Software},
    year = {2009},
    volume = {32},
    number = {7},
    pages = {1--17},
    url = {http://www.jstatsoft.org/v32/i07/},
  }