Pawn Promotion to Queen I have my rook on the 8th rank.  My pawn is directly behind it.  I want to move diagonal with my pawn to promote it to a queen.  Can I move diagonal to reach the 8th rank and promote my pawn?
You may do so only if the pawn is capturing one of the opponent's pieces; that is the only way a pawn ever moves diagonally. So here you can do what you describe:

[fen "3Rn3/k2P4/8/8/8/K7/8/8 w - - 0 1"]

1.dxe8=Q


But if you're talking about a situation like the following, then no, the pawn cannot move as you described:

[fen "3R4/k2P4/8/8/8/K7/8/8 w - - 0 1"]