I don't think there is a specific trap you can enable on the router for this.
You can enable syslogging for this event as follows
"ospf log-adjacency-changes"
If you are using Ciscoworks or a similar sysloger, you could set up the sysloger to send out an email alert when it recieves a syslog message caused by an ajacency change from your router.
This works because each syslog message has a unique MNEMONIC.
Cisco Works has a database of MNEMONICS and you can also add MNEMONICs to the database if they don't already exist.
You can then add an event based on a MNEMONIC such as send an email to x@x etc...which will run when a specific syslog message is received.
Not sure if this really helps you but the following link goes into more detail about syslog message structures.....
http://www.cisco.com/en/US/products/sw/iosswrel/ps1828/products_system_message_guide_chapter09186a0080080f07.html
Rgds,
Paddy
