Signatures of Duschinsky Rotation in Femtosecond Coherence Spectra

The motions of nuclei in a molecule can be mathematically described by using normal modes vibration, which form complete orthonormal basis. Each mode describes oscillatory motion at frequency determined the momentum nuclei. Near equilibrium, it is common to apply quantum harmonic-oscillator model, whose eigenfunctions intimately involve combinatorics. electronic state has distinct force constants; therefore, each normal-mode basis distinct. Duschinsky proposed linearized approximation transformation between bases two states rotation matrix. angles are typically obtained quantum-chemical computations or via gas-phase spectroscopy measurements. Quantifying condensed phase remains challenge. Here, we two-dimensional harmonic model that includes condensed-phase femtosecond coherence spectra (FCS), created transient–absorption measurements through impulsive excitation coherent vibrational wavepackets. Using 2D simulate identify signatures rotation. results suggest peak multiplicities and asymmetries may used quantify angle, key advance molecular spectroscopy.