C2v point group ($C_{2v}$)

A molecular point group with identity, one twofold axis, and two mirror planes containing that axis. With the twofold axis along $z$, its one-dimensional irreducible representations have Cartesian bases $z\sim A_1$, $x\sim B_1$, and $y\sim B_2$. For formaldehyde in the $xz$ plane, the vibrational representation is $3A_1+2B_1+B_2$.