create a new Web application  called http://domain.whatever2.com" target="_blank" rel="nofollow">http://domain.whatever2.com

stsadm.exe -o backup -url http://domain.whatever1.com/sites/sitename -filename
site.bak

stsadm.exe -o restore -url http://domain.whatever2.com" target="_blank" rel="nofollow">http://domain.whatever2.com -filename site.bak

If in the same farm, I would delete the original site  collection, as each is
identified by a GUID, and could cause issues down the road. Additionally, you
would require two databases if you decide not to delete the original anyway and
move it to the root of the existing Web app (GUID collision in the same DB)