Solvation Ultrafast Dynamics of Reactions. 10. Molecular Dynamics Studies of Dissociation, Recombination, and Coherence

Abstract

In this paper, the molecular dynamics of dissociation and recombination of iodine in argon clusters are reported and compared with the experimental results of the preceding paper et al. J. Phys. Chem. 1995, 99, 11309). The microscopic processes of bond breakage and bond reformation are visualized with the help of simple classical models. The coherent recombination observed experimentally is shown to be closely related to the coherent nature of bond breakage and the homogeneity of local structures in large clusters. Caging, which is found to be efficient in the large clusters, is ultrafast: The caging time scale ranges from femtoseconds to picoseconds depending on the bond breaking time as well as the size and temperature of the cluster. With the inclusion of the known solute (iodine) femtosecond dynamics and the solute-solvent LennardJones interaction potentials, the molecular dynamics simulations reproduce the corresponding experimental results and link the microscopic picture to the observables. We examine the effect of the local structure, cluster size and temperature, bond distance, and the state excited on the wave packet dynamics of the solute in the solvent. The new mechanism of coherent, concerted caging in the solvent structure is described. From the experimental and theoretical studies we provide some concepts regarding the molecular basis of the dissociation and recombination phenomena.

Photochemical processes in doped argon-neon core-shell clusters: The effect of cage size on the dissociation of molecular oxygen

“…8 Fluorescence spectroscopy is often used to identify the products of photochemical reactions in clusters, [9][10][11][12][13][14][15][16][17][18][19] and femtosecond laser excitation provides information on the time evolution of reactions. 20,21 Femtosecond photoelectron spectroscopy on mass selective iodine Ar anion clusters showed that a solvation shell of 20 Ar atoms was sufficient to induce recombination of the iodine fragments 21,20 and similar experiments on iodine in neutral Ar clusters revealed that caging was completed within 10 −12 s. [22][23][24] A thorough investigation of the cage effect of hydrogen halides doped into the interior or onto the surface of clusters and aligned in a static electric and a laser field was recently undertaken by Buck and co-workers. [25][26][27][28][29][30] They measured the kinetic energy of the hydrogen atom as a function of the orientation and showed that the dissociation of hydrogen halides can even be inhibited on the cluster surface because the light hydrogen carries almost all the kinetic energy and is caged by the cluster and the heavy halogen atom.…”

Molecular Dynamics Simulation of Dissociation Kinetics

“…7,8,9 Dissociation takes place when the potential between two atoms of an oxygen molecule exceeds some critical value. The point at which this occurs is relatively ambiguous because it is difficult to explicitly define the point on the Morse potential curve where the molecule dissociates.…”

“…To account for this, the atoms' velocities are scaled to adjust their kinetic energy to match the change in potential so the total energy of the system remains constant. 7 Subsequently, as the atoms move with their new velocities, they affect their neighbors. In the case of recombination, the energy released by the creation of an oxygen molecule is transferred to the surrounding atoms by this process.…”

Intramolecular vibrational energy relaxation in nitrous acid (HONO)

“…Vibrational energy relaxation of diatomic molecules in matrix environment has been studied in great detail. [8][9][10] The HONO system has been studied intensively both theoretically 6,7,[11][12][13][14][15][16][17][18][19][20][21][22][23] and experimentally. [3][4][5][24][25][26][27][28][29] Neither experimental 30 nor theoretical 12,20 studies could find the reaction taking place in the gas phase with significant yields; hence, isomerization seems to be facilitated by the dissipative forces of the matrix environment.…”