Cluster impact chemistry. High-energy collisions of I2ArN clusters with a Pt surface

Abstract

In this paper, we explore cluster–surface impact induced dissociation of an I2 molecule initially embedded within an I2ArN (N=11–553) cluster, which collides with a Pt surface. Molecular dynamics simulations of high-energy I2ArN–Pt surface collisions (with initial center of mass velocities v=0.2–10 km s−1 and initial kinetic energies E0K=1 eV−1.2×104 eV) provide information on the yields and time scales for energy acquisition by the cluster and by the surface and energy deposition to the guest molecule via the formation of an intracluster microscopic shock wave, as well as on the I2 dissociation dynamics. The intracluster shock wave is characterized by a temporal peak in the cluster potential energy and in the saturation of the cluster temperature, with the sum of the yields for potential and kinetic energy deposition into the cluster being 0.5–0.6. The cluster residence time (τ=50–800 fs over our velocity and cluster size domain) coincides (within 20%) with the time scale for the cluster energy acquisition, decreasing linearly with v−1 and obeying a dynamic size equation τ∝(N+2.9)1/3. The characteristic time tp for energy deposition to the I2 molecule via a local mechanism involving pair interactions is also close to τ. The initial cluster kinetic energy dependence of the dissociation yields YD of I2 reveals a gradual increase of YD towards unity above a threshold at the energy Et. For smaller (N=11,53) clusters, Et/N is close to the dissociation energy of bare I2, while for larger clusters Et exhibits an exponential N dependence. Cluster impact dissociation of I2 in I2ArN results in higher YD values (≳0.4) than the high-energy collision of bare I2 with the Pt surface for which YD saturates at 0.35. The I2 dissociation times 〈τD〉, which were characterized by averaging over the first passage times for the attainment of the turning point of the I–I intramolecular Morse potential for reactive trajectories, fall in the range 170–800 fs, exhibiting a marked inverse kinetic energy dependence, revealing an increase with increasing cluster size and obeying the rough relation 〈τD〉≂2τ, i.e., being proportional to the cluster radius. Energy acquisition and dissociation times are comparable to or even shorter than the vibrational time [τ(I2)=156 fs] of the I2 molecule, opening up a new research area of thermal femtosecond chemistry.

Low energy acetone dimer ion/surface collisions studied with high energy resolution

“…In particular, we have been able -as predicted by Cleveland and Landman [14] (see also [15,[36][37][38][39]) using molecular-dynamics simulations -to observe here besides surface induced dissociation (SID) also surface induced reactions (SIR) of acetone dimer ions upon impact on a hydrocarbon covered stainless steel surface. Using fully deuterated acetone dimer ions we obtained evidence for the occurrence of two competing surface-induced reactions, i.e., on the one hand intra-cluster ion molecule reactions leading to the production of the deuteronated acetone monomer ion (CD 3 COCD 3 )D + and on the other hand hydrogen pick-up reactions leading to the formation of the protonated acetone monomer ion (CD 3 COCD 3 )H + .…”

Molecular dynamics simulations of the micro-solvation of ions and molecules during cluster–surface collisions

“…The surface impact induced disintegration of the cluster transfers the embedded ions into the gas phase as free solvated ions that straightforwardly can be analyzed in a mass spectrometer. To apply this method in a wider context, detailed knowledge of the dynamics of the cluster-surface collision is necessary, e.g., to avoid driving the chemical reactions under study, as has been observed for high-energy cluster-surface impact [9,10].…”

Conditions for the emergence of life on the early Earth: summary and reflections

“…A microscopic physical analogue for macroscopic impact events is provided by high-energy cluster-wall collisions. Such processes are triggered by the acceleration of atomic and molecular cluster ions (containing 10-10 4 constituents with velocities up to approximately 100 km s K1 and kinetic energies up to 100 eV per particle), which collide with a molecular or metal solid surface (Schek et al 1994;Schek & Jortner 1996). Thermal femtosecond dynamics of these high-energy clusters (Schek et al 1994) provide a medium for reactive processes, such as dissociation of diatomics embedded in the colliding cluster (figure 2).…”

“…Such processes are triggered by the acceleration of atomic and molecular cluster ions (containing 10-10 4 constituents with velocities up to approximately 100 km s K1 and kinetic energies up to 100 eV per particle), which collide with a molecular or metal solid surface (Schek et al 1994;Schek & Jortner 1996). Thermal femtosecond dynamics of these high-energy clusters (Schek et al 1994) provide a medium for reactive processes, such as dissociation of diatomics embedded in the colliding cluster (figure 2). More interestingly, these impact phenomena induce novel and isoteric chemical processes, such as the N 2 CO 2 /2NO reaction of the burning of nitrogen (Raz & Levine 2001), providing a basis for novel chemical reactions.…”

“…The dissociation of I 2 is manifested. Data were adopted from Schek et al (1994). High-energy wall collisions of clusters containing prebiotic material or biotic molecules can provide a unique chemical medium for the shock-impact synthesis of building blocks of biomolecules or amino acid oligomers.…”