Dynamics of l-Phenylalanine Sputtering by Argon Cluster Bombardment

Abstract

We simulate the impact of an Ar 1000 cluster (energy 10 keV, impact angle 55°) into an amorphous L-phenylalanine target. By use of a ReaxFF potential, it is possible to model not only the emission dynamics of intact Phe molecules but also the fragmentation and reaction pathways taken. The simulated sputter yield is in close agreement with experiment. The simulated emission mass spectrum features both emission of large Phe n clusters and entrainment of reaction products in the ejected flow, again in agreement with experimental observation. While H abstraction is a common fragmentation channel, the H radicals quickly combine with Phe in the amino group; no isolated H atom is ejected.

Molecular cluster emission in sputtering of amino acids by argon gas-cluster ions

“…The data may indicate that the fall-off of the cluster yields with cluster size is more gradual for amino acids with a higher sputtering yield while it is stronger for those with low yields. The abundant formation of such cluster species was also observed in recent MD simulations [43] of phenylalanine sputtering by argon cluster bombardment. These data show that the impinging cluster excavates a deep crater of almost hemispherical shape in the target from which material is profusely ejected, while crater walls and ejecta are strongly energized.…”

“…More recently, a prolific cluster emission from phenylalanine was observed [42], exhibiting an abundant flux of protonated molecular cluster ions (M n +H) + with n ≤ 12. An MD simulation of phenylalanine sputtering by Ar 1000 cluster bombardment also demonstrated the emission of (very) large phenylalanine cluster [43], showing even the formation of a cluster composed of 38 phenylalanine molecules.…”

“…A lower limit might be given by the diameter of the crater formed upon impact of an individual Ar cluster ion which constitutes the emission site of sputtered species. For the present situation a typical value would be ∼5 nm [31,43]. In future experiments different preparation procedures for such mixtures might be explored in order to obtain a more homogeneous spatial distributions of two or more amino acids.…”

Irradiation of astrophysical ice grains by cosmic-ray ions: a REAX simulation study

“…In view of the fact that molecules may be vibrationally excited the distance must be chosen larger than the equilibrium bond length. We chose a value of d = 1.7 Å for C, N, and O atoms; while for H we adopted 1.3 Å (Mücksch et al 2014). This scheme allows for an efficient dynamic grouping of all atoms in the irradiated target into molecules.…”

“…This scheme allows for an efficient dynamic grouping of all atoms in the irradiated target into molecules. We have used it previously in several instances (Anders & Urbassek 2007Mücksch et al 2014). …”