Powershell hashtable keys with special characters

I'm having trouble trying to access a hashtable with a / in the key. In my case the keys are mime types, and a simple example of the hashtable looks like:

PS H:\> $h

Name                           Value                                                                                                                         
----                           -----                                                                                                                         
application/pdf                {application/pdf, application/pdf}

When I try to do access by the Key name, I am not getting any results:

   PS H:\> $h."application/pdf"

   _______________________________________
   PS H:\> $h["application/pdf"]

   _____________________________________________
   PS H:\>

What is going on here, and how to I use this key?