Simulation of the UV Absorption Spectrum

The UV absorption spectrum in the energy range between 3.8 and 5.7eV consists in two distinct bands, dominated by absorption to the and B2u(Tnr ) states. 

The spectrum computed with the two-state model is presented in Fig. 5.3b. In this case, damping times t of 400 and 40fs were used for the B uin-K ) and B2 (7r7r ) components, respectively. The whole spectrum was blue-shifted by 0.04 e V. The two-state model qualitatively reproduces the shape of the B2 (7r7r ) band. A closer look 

The spectrum computed with the four-state model is presented in Fig. 5.3d. Damping times t of 400 and 100 fs were used for the Bsuinir ) and components, 

The results presented in this section allow us, by taking into account the overall energy shift and the adjustment of the (mr ) state vertical excitation energy applied 

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From the theoretical point of view, this relaxation process has been the subject of a large number of quantum dynamics investigations, based on reduced and full dimensional models. Farly works [13-17] reported three- and four-mode models and showed that a simple two-state four-dimensional model provides a qualitatively correct simulation of the UV absorption spectrum [17], These models were used to simulate various spectroscopic signals, including time-resolved transient absorption [18-20], and ionization [21] spectra, fluorescence [22] and resonance Raman spectra [23]. Worth et al. [24-27] performed accurate quantum dynamics simulations based on a model including the twenty-four vibrational modes of the molecule using the MCTDH method. These benchmark results have then been used to test various approximate methods for the simulation of non-adiabatic dynamics of molecular systems [28 0]. 

Quantum dynamics simulations of the UV absorption spectrum and of the electronic state population dynamics of the molecule excited by a short laser pulse resonant with the transition to the bright B2u t t ) state, based on the models described in Sect. 5.3 were performed using the MCTDH method in the multi-set formalism (see Sect. 4.2.5 in Chap. 4). For the representation of the Hamiltonian and the wave function, a Hermite polynomial DVR scheme [60] was used for all the degrees of freedom. The number of SPF and primitive basis functions used in the calculations are listed in Table 5.4. Test calculations with both larger primitive and SPF bases have been... 

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