The breaking and remaking of a bond: Caging of I2 in solid Kr

Abstract

The caging of I2 in solid Kr is followed in real-time following its dissociative excitation on the A (31'1 t .) surface. The experiments involve pump-probe measurements with a time resolution of 2 150 fs. The experimental signals are reproduced using classical molecular dynamics simulations, and the classical Franck approximation. The comparison between experiment and simulation allows an unambiguous interpretation of features in the observed signal as being due to the initial impulsive stretch of the I-I bond, collision of the atoms with the cage wall, recoil and recombination, and the subsequent coherent oscillations of the nascent I, molecule. These detailed observations are possible due to retention of coherence along the I-I coordinate throughout the caging process. The extent of coherence is dictated mainly by the initial impact parameters of the molecule-cage collision, which in turn is controlled by the thermal and zero-point amplitudes of lattice vibrations. The caging is well-described as a sudden process, involving a binary collision between I and Kr atoms with nearly complete energy loss of the I atom upon completion of the first collision. Vibrational relaxation of the bound molecule proceeds on the time scale of 12 ps. The nontrivial relation between this relaxation time and decay rates that may be extracted from experimental transients is discussed. Although the interplay between the nested A and A ' potentials is not detectable, it is clear that in the studied range of initial excess energies, 1000-1700 cm-', the recombination remains effectively adiabatic, and does not involve the ground state.

A classical molecular dynamics study of recombination reactions in a microporous solid

“…In fact their cooperative behavior is responsible for any encounter between the species, and it exerts a relevant influence upon the microscopic mechanism of the reaction. 13,14 The present work concerns the study of the geminate recombination reaction of two photodissociated atoms occurring in two different environments: a liquid one ͑tetrachloromethane, represented as spherical structureless particles͒, and a solid one ͑a zeolite, that is a microporous crystalline silicate 15 ͒. Zeolites are routinely used as heterogeneous catalysts in a very diverse range of catalytic reactions.…”

Dynamics of excited tetrakis(dimethylamino)ethylene solvated by argon atoms

“…The present effect where the argon atoms that have to be pushed away, are hindering the molecular deformations differ from the usual caging dynamics of a dissociating molecule by a solvent, as exemplified by the dissociation of I 2 in rare gases [57,58] or that of Cl 2 molecules within large xenon clusters [59]. The caging dynamics of molecular dissociation appears indeed as a hard sphere collision of the departing halogen atoms with the surrounding atoms.…”

Electronic spectroscopy of I2–Xe complexes in solid Krypton

“…There is an increase in the sideband at 400 nm in the panel (b) but this may be due to emission from the first IP tier states. Time-domain pump-probe dynamics of the I 2 A( 3 1u )-state has been analyzed with great detail in the rare gas matrices, 4,[45][46][47] mainly from the point of view of cage recombination and predissociation to the A state. The negative time signal in the panel (c) reflects slow Kr cage dynamics 25,48 (period ∼630 fs) seen through the first IP tier emissions.…”