Computed vibrational normal modes are represented: panel A is the IR spectrum of ; panel B is the IR spectrum of (pgn) (e-P₂); panel C is the IR spectrum of (e,e-P₂); panel D is the IR spectrum of (d,2e-P₂); panel E is the IR spectrum of (2d,2e-P₂); panel F is the IR spectrum of (3d,2e-P₂); panel G is the IR spectrum of C₅H₉NO₂. Using the 6-311++G^** basis set. The black line is the simulated spectra by Gaussians with a full width half-maximum of 4 cm⁻¹.