what gambit is this? its  very effective opening

domination of the center

It is called the Center Game Accepted.  Generally white gets punished for bringing its queen out so early.

I see this post is kind of old...no one has given you much positive feedback on this idea of Qxd4, obviously because no one has studied the lines.  Normally, the queen after Nc6 will retreat to e3, where she is flexible enough to travel to the kingside.  Do a bit of research on it and see if you like it.  It isn't fair to just say, "generally white gets punished"....generally speaking can mean anything.

The Ruy Lopez was not a valued opening at one point - the King's Gambit was much better, but now the times have changed.  The King's Indian used to not be a good opening, but now times have changed.  Same goes for countless openings, where a genius all of a sudden figured out how to get a decent position...how about the Petroff...useless for centuries I believe, until petroff discovered 3...d6. 

Please, chesschamp, take my advice.  If you don't get any good advice here, keep looking until you find your answers.  I will give you a link to some cool ideas in this opening...

http://en.wikipedia.org/wiki/Center_Game

http://www.chesscafe.com/text/kibitz103.pdf

It may sound funny, but Tim Harding, who is a regular writer and great player, notes that the move was a surprise to him...2.d4! Good surprise value. 

Here is another note: If you study the opening, you will see that you have SO many playable options after e4 e5 d4 exd than just Qxd.  You could easily have 10 openings to pull out of a bag and trick your opponents, including the Scotch Opening and Gambit, The Danish Gambit, etc...

My advice...play it and love it!

thanks alot

 

The opening is very frowned upon. It's not really a gambit, though. The side that activates the queen regains the pawn. But the other side regains the lost tempo by activating the queenside knight. After that, the queen can easily become a target for minor pieces. In general, it's a bad idea to move out the queen early.

its not a bad idea to move the queen out early you can influence the center

That's not bad, although I've always thought of that opening as 'junk' because then black can move the other knight out and be 'a tempo ahead'... however that's not the whole story. But if you know me, I'd always go for

i.                     P-K4               P-K4

ii.                   P-Q4              PxP

iii.                  P-QB3           PxP

iv.                 B-QB4           PxP

v.                   BxP

(V. …B-QKt5 ch. VI. Kt-Q2 or Kt-QB3 followed by either P-QR3 or Q-QKt3, etc.)

The two pawn Danish gambit, an extreme attacking opening...

The Gambit King