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In this paper the phenomenon of the ultrafast relaxation of a system coupled to a small bath is treated. The system, representing the pyrazine molecule, contains 4 vibrational modes and 2 electronic states coupled via a conical intersection, and the bath is a set of up to 20 harmonic oscillators. The dynamics of the complete system are described by wave packet propagation using the multiconfiguration time-dependent Hartree method. By the use of multidimensional single-particle functions it was possible to obtain results of a high quality, even for the complete system with 24 degrees of freedom. The full wave function for the system and bath are analyzed to reveal the characteristics of the system-bath interaction, such as energy transfer to the bath, or the effect of the bath on the state populations. The results show that the damping due to the bath model adopted is not only nonhomogeneous but also selective: certain high frequencies are found to remain at long times.

The multiconfigurational time-dependent Hartree (MCTDH) approach is applied to an example showing very complex dynamics: the wave-packet dynamics on the three-dimensional B2 potential-energy surface of NO2. The ability of the MCTDH scheme to describe accurately the severe splitting of the wave packet on a saddle-shaped surface is demonstrated. Internal checks of the MCTDH calculation enable us to assess the degree of convergence without the need to resort to a numerically exact wave-packet calculation. As a representative observable the photodissociation spectrum is calculated and discussed. The A1/B2 vibronic coupling is neglected in our study, but the dynamics on the diabatic B2 surface is treated in its full three dimensionality.

The derivation of the transformative complex absorbing potential (TCAP) method and its performance are discussed. This approach was developed in a previous paper (1995 J. Phys. B: At. Mol. Opt. Phys. 28 1475 and illustrates the relation between complex absorbing potentials (CAPs) and the smooth exterior scaling (SES) method. Starting from an energy-dependent CAP one arrives at an SES-like Hamiltonian via an elementary similarity transformation. Developing this idea further leads to the so-called TCAP equation. It differs from the SES Schrödinger equation in two respects. Firstly, the potential is not transformed and, secondly, an additional correction term appears. Neglecting this rather small term leads to a Hamilton operator that is easy to apply to time-dependent as well as time-independent problems. This Hamiltonian can be extended order by order ending up in the full SES Hamiltonian. By numerical application it is demonstrated that the TCAP approach is very efficient and can easily be generalized to the multi-dimensional case for which formulae are provided.

The interatomic Coulombic decay (ICD) in the Ne dimer is discussed in view of the recent experimental results. The ICD electron spectrum and the kinetic energy release of the Ne+ fragments resulting after Coulomb explosion of Ne2 (2+) are computed and compared to the measured ones. A very good agreement is found, confirming the dynamics predicted for this decay mechanism. The effect of the temperature on the electron spectrum is briefly investigated.