literature copyright laws and public domain

     I am interested in adapting a screenplay from a story written by Edgar Allen Poe. Specifically, the story is "The Facts in the Case of M. Valdemar." I am wondering if this story is public domain or if it is copyrighted and if so, how I can go about trying to get permission to use it. I want to make the screenplay into a short film. If you can help me or direct me to where I can get help, it would be much appreciated.

                                    Thanks,
                                    Chris Randall
                                    randallc[_at_]river.it.gvsu.edu