Actually, Van Persie was facing the assistant referee when he got the ball. It was a stupid yellow card, but a yellow card, did he forget he had already a yellow card? Whether the main referee could have avoided it? Debatable, I think Van Persie was out of his mind in the first half and with 1-1 he delibertely went to lose time knowing the flag was up. Not a bright decision from Van Persie.
By the way, there was a penalty and an (unfarily) disallowed goal for Barcelona in the first game and I believe a penalty today in the first half. Guardiola did not complain after the first game, what Wenger did today is not good, Arsenal never shot to the goal today, to say that with Van Persie they would have won the game, sad comment, mourinho-style.
Intersting story about the game with the argentineans.