[Sch6543]

I have been given this task, which reads:

Determine with two vectors on the y-bridge-hydrogen atoms as the basic look and the symmetry  to the two oscillations which these hydrogen atoms being perpendicular B2H2 plan.

Some can help me understand how I can find the irreducible representations?

[mjc123]

Look at this thread: http://www.chemicalforums.com/index.php?topic=82538.0

[Sch6543]

I think so, but I'm not sure

E = 4
C2(z) = 0
C2(y)= 2
C2(x)= 0
i =0
sigma(xy) = 1
sigma(xz) = 0
sigma(yz) = 1

[mjc123]

Are you using the right point group? You look as if you're using D_2h, which is the point group of B₂H₆, not B₂H₄.
What is the set of four things you're trying to find the representation of?