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The sequential photodissociation dynamics of (HI)2 is studied by means of a nonadiabatic wave packet treatment starting from the I*-HI complex. The model reproduces the main experimental findings for photolysis with 266 nm radiation. The results confirm that some of the H atoms dissociated from the I*-HI complex deactivate the I* atom through a H/I* intracluster collision which induces an I*→I electronically nonadiabatic transition. As a consequence, these H fragments become very fast by acquiring nearly all the I* excitation energy, equivalent to the I*/I spin-orbit splitting. A most interesting result is the high production of bound I2 fragments in highly excited rovibrational states in the photolysis, indicating that the H dissociation is mainly direct. [ABSTRACT FROM AUTHOR]

We calculate the alignment and orientation of the CN fragment of the photodissociation of ICN using a time-dependent method and the diabatic potentials and transition moments of Morokuma and co-workers [J. Chem. Phys. 100, 4894 (1994)]. The time-dependent Schrödinger equation is solved using a Chebyshev method evaluating sums required to do the matrix-vector products sequentially. To prevent the wave packet from drifting off the edge of our grid we propagate in successive steps. The ground state wave function, from which the molecule is dissociated, is computed using a three-dimensional variational method. We calculate alignment and orientation for a Ji=0→Jf=1 transition. We use parity-adapted angular basis functions. Our calculated alignment and orientation are qualitatively close to experimental results. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The influence of parent molecule bending motion on nonadiabatic transitions during photodissociation is investigated using a model involving two linear excited-state surfaces. The two dissociative states are strongly coupled near the so-called conical intersection. Due to symmetry constraints, the two adiabatic surfaces are not allowed to interact in linear configurations and the coupling is only switched on when the molecule is bent. Therefore, electronic transitions from one adiabatic surface to another are only possible when the dissociation process involves bending motion. A quantum-mechanical model including both the dissociation and bending degrees of freedom is established to assess the importance of parent bending motion on nonadiabatic transition dynamics. The coupling between the two electronic states is explicitly taken into account and the dissociation dynamics is described by a time-dependent wave packet. Although the approach is applicable to any triatomic molecular systems, we choose to model a pseudotriatomic system, i.e., methyl iodide CX3I (X=H, D, etc.). In our calculations, the three X atoms are treated as a single pseudoatom and the C–X3 umbrella bending coordinate is frozen at its equilibrium geometry. The two dynamically active coordinates are the I–CX3 stretch and the I–C–X3 bend. Both the ground and two excited states are represented by linear potential-energy surfaces and the coupling of the two dissociative surfaces is a conical intersection in nature. Several dissociation processes are modeled with different initial bending wave functions and different isotopic substitutions. It is found that parent bending motion has a significant effect on the final electronic branching of dissociation fragments. The calculation generates a larger I* yield from the CD3I dissociation than that from CH3I, in agreement with experimental observations which could not be reproduced by previous theoretical calculations. Our... [ABSTRACT FROM AUTHOR]

The Gaussian wave packet method has been developed for the simulation of processes like molecular collisions, photodissociation of molecules, and laser excitations of molecules. So far a necessary condition for an accurate result is that the fragment states are propagated accurately. We have considered one-dimensional bound states described by a Morse potential, and carried out a systematic study of the ability of the Gaussian wave packet method to propagate the stationary states. It is found that the complete set of equations of motion as derived by the minimum error method (MEM) cannot be used in practical calculations because of numerical problems. These are eliminated by the introduction of simplifications such as the independent Gaussian approximation (IGA), where each wave packet is propagated independently. The conditions for an accurate propagation within that assumption are developed, and a simple method is devised to identify those states, which are propagated accurately. This procedure may be used to investigate when the Gaussian wave packet method is appropriate for the simulation of a given process. [ABSTRACT FROM AUTHOR]