[PF] Strength Surge rage power specifics

[gr8artist]

Can a barbarian use Strength Surge (http://www.d20pfsrd.com/classes/core-classes/barbarian/rage-powers/paizo---rage-powers/strength-surge-ex) after rolling a combat maneuver check, but before knowing if his roll succeeded or failed?

Can a barbarian use Strength Surge (http://www.d20pfsrd.com/classes/core-classes/barbarian/rage-powers/paizo---rage-powers/strength-surge-ex) after failing a CMB or CMD check in hopes to succeed on that check?

Strength Surge (Ex):
Benefit: The barbarian adds her barbarian level on one Strength check or combat maneuver check, or to her Combat Maneuver Defense when an opponent attempts a maneuver against her. This power is used as an immediate action.
Special: This power can only be used once per rage.

Our group is having a little trouble pinpointing when EXACTLY an immediate action can be used. The barbarian want to declare his action, then roll his check, then activate strength surge if his check is low, and then compare his total to the enemy CMD.
We've argued that an immediate action is a specific unit of time that can't be placed within a standard action, but we have no proof or evidence to support this... also, we might be wrong.

[Vastly]

Well, I think the RAI answer is, no, it can't be used after the roll has been made.

I believe the immediate action is generally for an action that be used as a reactive defense to an attack. Which in this case, Strength Surge can be used when a combat maneuver is used against him and he wants to use it to bolster his CMD.

Now the ability doesn't specifically state that use must be declared before the roll is made, nor does it state that it can be used after the result of the roll is determined. And an immediate action is one that can occur outside of your turn and before a result occurs. This leaves it somewhat unclear.

So unless there is a ruling I'm forgetting, by RAW, it'd be up to the DM. If I were running the game, I'd say no, use must be declared before the roll is made.