For H2O molecule, the electronic transition from the ground state to an excited state of B1 symmetry is 

\(\begin{array}{c|ccccc} C_{2 v} & E & C_2 & \sigma_v & \sigma_v^{\prime} & \\ \hline A_1 & 1 & 1 & 1 & 1 & z, z^2, x^2, y^2 \\ A_2 & 1 & 1 & -1 & -1 & x y \\ B_1 & 1 & -1 & 1 & -1 & x, x z \\ B_2 & 1 & -1 & -1 & 1 & y, y z \end{array}\)