| In this dissertation, the time-dependent wave packet methods were used to study in detail the photodissociation dynamics of diatomic molecular systems. In addition, the Rosen-Zener-Demkov(RZD)coupling model and the Landau-Zener theoretical model was applied to study the nonadiabatic processes that may be happened during the dissociation pathways. The main research results are shown as follows:(1) The dissociation processes of Cl2 molecule have been studied at photolysis wavelengths range of 310-470 nm using time-dependent wave packet method. The initial wave packets are propagated on the excited state potentials utilizing the splitting operator technique. The excitation cross-sections are calculated numerically by extracting the dynamics information at a large internuclear separation. The calculated excitation cross-sections suggests that the C state plays a major role around 330 nm, while the A and B states are expected to make significant contribution on the longer wavelength side. Applying the Rosen-Zener-Demkov (RZD) model, the radial non-adiabatic transition probabilities from C1Î u to 1u(â…¢) electronic state are predicted, the branching ratio of various product channels and anisotropy parameterβ(Cl*) are determined as well. Finally, the kinetic energy distributions of fragments are obtained in the asymptotic region. The results show that the RZD model holds for the calculation of non-adiabatic pathway in the dissociation region of Cl2. The strong coupling strength existing between C1Î u and 1u(â…¢) states is the main origin to yield Cl* with negative anisotropy parameterβ(Cl*) as wavelength shorter than 330 nm. The non-adiabatic transition effects can be neglected as wavelength beyond 380 nm.(2) The photodissociation dynamics of HI molecule has been studied in the region of 31000-45000 cm-1 (within the A spectrum band range) using quantum-mechanical wave packet simulation in conjunction with the splitting operator propagation scheme. Employing the computed ab initio potential energy curves and the relevant transition moment functions, partial cross-sections and total cross-section for the A band states in this range are derived, and the branching fractionΓ(I*) of atomic I* is determined as a function of excitation wave numbersν. The results shown that the branching fraction has a maximum about 0.54, and the calculatedΓ(I*) function agrees with the experimental measurable except in the excitation energy range of 37000-40000 cm-1. The one-dimensional Landau-Zener model is proposed firstly to examine the possibility that nonadiabatic transition exists in the dissociation process over low energy part of the A-band range. The relative quantum yield and angular anisotropy data of I* fragments in reference, coupled with the dynamical results that partial cross-sections of 3Î 1, 3Î 0+, 1Î 1â†X obtained, are used in deriving analytical curve-crossing probability and further adopted to evaluate the behavior of curve crossing by applying the Landau-Zener model. The results suggest that the contribution of nonadiabatic mechanism to the A band photofragmentation, which may be caused by spin-rotational coupling, is not significant over low energy part of the A-band and thus can be ignored, although the angular distribution is less anisotropic in this energy regime(3) The photodissociation of Br2 molecule has been investigated at its visible-near UV absorption band in the range 350-580 nm using the dynamical simulation. Based on the ab initio computation for the ground state and low-lying excited states of the Br2 molecule, the optical cross-sections for the discrete transitions of A3Î 1u, B3Î 0+u, C1Î uâ†X1Σg+ (ν?=0) and their total energy absorption cross-section are derived, and the quantum yield of (Br+Br*) channel are determined as a function of excitation wavelength, which is consistent with most of the previously measured data. The one-dimensional Landau-Zener model is used to evaluate the behavior of curve crossing during photodissociation. The results indicate that the influence of nonadiabatic mechanism, which may be caused by the electronic-vibrational interaction between the B and C states, is negligible small for the (Br+Br*) channel. From the Landau-Zener modeling of the observed product recoil parameterβ(Br+Br), the best-fit value of the coupling matrix element or coupling strength between the diabatic B and C state potentials is obtained as VB/C=10 cm-1 in the present study, which accounts for the wavelength dependence of anisotropy parameter of Br+Br product from 460 to 560 nm.
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