Simulations of vibronic profiles in two-photon absorption

We propose and evaluate an approach for simulating vibronic profiles in two-photon absorption (TPA) of polyatomic molecules accounting for both Franck-Condon and Herzberg-Teller couplings. A linear coupling scheme is implemented in which the multi-dimensional vibronic coupling constants are obtained from ground state frequencies and normal coordinates and excited state energy gradients evaluated at the ground state equilibrium geometry. Applications on charge-transfer monomer and dimer molecules based on trans-polyene indicate the importance of vibrational TPA profiles in experimental predictions and comparisons. (C) 2000 Elsevier Science B.V. All rights reserved.